1.
Left- and right-hand traffic
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This is so fundamental to traffic flow that it is sometimes referred to as the rule of the road. About two-thirds of the population use RHT, with the remaining 76 countries and territories using LHT. Countries that use LHT account for about a sixth of the worlds area, in the early 1900s some countries including Canada, Spain, and Brazil had different rules in different parts of the country. During the 1900s many countries standardised within their jurisdictions, and changed from LHT to RHT, in 1919,104 of the worlds territories were LHT and an equal number were RHT. From 1919 to 1986,34 of the LHT territories switched to RHT, many of the countries with LHT are former British colonies in the Caribbean, Southern Africa, Southeast Asia, Australia, and New Zealand. Japan, Thailand, Nepal, Bhutan, Mozambique, Suriname, East Timor, in Europe, only four countries still drive on the left, the United Kingdom, Ireland, Malta, and Cyprus, all of which are islands. Nearly all countries use one side or the other throughout their entire territory, most exceptions are due to historical considerations and involve islands with no road connection to the main part of a country. China is RHT except the Special Administrative Regions of China of Hong Kong, the United States is RHT except the United States Virgin Islands. The United Kingdom is LHT, but its overseas territories of Gibraltar, according to the International Regulations for Preventing Collisions at Sea, water traffic is RHT. For aircraft the US Federal Aviation Regulations provide for passing on the right, light rail vehicles generally operate on the same side as other road traffic in the country. Many countries use RHT for automobiles but LHT for trains, often because of the influence of the British on early railway systems, in some countries rail traffic remained LHT after automobile traffic switched to RHT, for example in China, Brazil, and Argentina. However, France, Belgium, and Switzerland have used RHT for automobiles since their introduction, there is no technical reason to prefer one side over the other. Ancient Greek, Egyptian, and Roman troops kept to the left when marching, in 1998, archaeologists found a well-preserved double track leading to a Roman quarry near Swindon. The first reference in English law to an order for LHT was in 1756, northcote Parkinson, believed that ancient travellers on horseback or on foot generally kept to the left, since most people were right handed. If two men riding on horseback were to start a fight, each would edge toward the left, in the year 1300, Pope Boniface VIII directed pilgrims to keep left. In the late 1700s, traffic in the United States was RHT based on use of large freight wagons pulled by several pairs of horses. The wagons had no seat, so a postilion sat on the left rear horse. Seated on the left, the driver preferred that other wagons pass him on the left so that he could be sure to keep clear of the wheels of oncoming wagons, in France, traditionally foot traffic had kept right, while carriage traffic kept left
2.
Moon
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The Moon is an astronomical body that orbits planet Earth, being Earths only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, following Jupiters satellite Io, the Moon is second-densest satellite among those whose densities are known. The average distance of the Moon from the Earth is 384,400 km, the Moon is thought to have formed about 4.51 billion years ago, not long after Earth. It is the second-brightest regularly visible celestial object in Earths sky, after the Sun and its surface is actually dark, although compared to the night sky it appears very bright, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its cycle of phases have made the Moon an important cultural influence since ancient times on language, calendars, art. The Moons gravitational influence produces the ocean tides, body tides, and this matching of apparent visual size will not continue in the far future. The Moons linear distance from Earth is currently increasing at a rate of 3.82 ±0.07 centimetres per year, since the Apollo 17 mission in 1972, the Moon has been visited only by uncrewed spacecraft. The usual English proper name for Earths natural satellite is the Moon, the noun moon is derived from moone, which developed from mone, which is derived from Old English mōna, which ultimately stems from Proto-Germanic *mǣnōn, like all Germanic language cognates. Occasionally, the name Luna is used, in literature, especially science fiction, Luna is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of our moon. The principal modern English adjective pertaining to the Moon is lunar, a less common adjective is selenic, derived from the Ancient Greek Selene, from which is derived the prefix seleno-. Both the Greek Selene and the Roman goddess Diana were alternatively called Cynthia, the names Luna, Cynthia, and Selene are reflected in terminology for lunar orbits in words such as apolune, pericynthion, and selenocentric. The name Diana is connected to dies meaning day, several mechanisms have been proposed for the Moons formation 4.51 billion years ago, and some 60 million years after the origin of the Solar System. These hypotheses also cannot account for the angular momentum of the Earth–Moon system. This hypothesis, although not perfect, perhaps best explains the evidence, eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists, You have eighteen months. Go back to your Apollo data, go back to computer, do whatever you have to. Dont come to our conference unless you have something to say about the Moons birth, at the 1984 conference at Kona, Hawaii, the giant impact hypothesis emerged as the most popular. Afterward there were only two groups, the giant impact camp and the agnostics. Giant impacts are thought to have been common in the early Solar System, computer simulations of a giant impact have produced results that are consistent with the mass of the lunar core and the present angular momentum of the Earth–Moon system
3.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
4.
Far side of the Moon
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The far side of the Moon is the hemisphere of the Moon that always faces away from Earth. The far sides terrain is rugged, with a multitude of impact craters and it has one of the largest craters in the Solar System, the South Pole–Aitken basin. About 18 percent of the far side is visible from Earth due to libration. The remaining 82 percent remained unobserved until 1959, when the Soviet Unions Luna 3 space probe photographed it, the Soviet Academy of Sciences published the first atlas of the far side in 1960. In 1968, the Apollo 8 missions astronauts were the first humans to view this region directly when they orbited the Moon, to date, no human being has ever stood on the surface of the far side of the Moon. Astronomers have suggested installing a large telescope on the far side. Tidal forces from Earth have slowed down the Moons rotation so that the side is always facing the Earth. The other face, most of which is never visible from the Earth, is called the far side of the Moon. Over time some parts of the far side can be due to libration. In total 59 percent of the Moons surface is visible from Earth at one time or another, useful observation of the parts of the far side of the Moon occasionally visible from Earth is difficult because of the low viewing angle from Earth. While many misconstrue this to think that the dark side receives little to no sunlight, in reality, however, the near side also receives sunlight reflected from the Earth, known as earthshine. Earthshine does not reach the area of the far side which cannot be seen from Earth, only during a full moon is the whole far side of the Moon dark. The word dark has expanded to refer to the fact that communication with spacecraft can be blocked while on the far side of the Moon. The two hemispheres have distinctly different appearances, with the near side covered in multiple, large maria, the far side has a battered, densely cratered appearance with few maria. Only 1% of the surface of the far side is covered by maria and it has also been proposed that the differences between the two hemispheres may have been caused by a collision with a smaller companion moon that also originated from the Theia collision. The far side has more visible craters and this was thought to be a result of the effects of lunar lava flows, which cover and obscure craters, rather than a shielding effect from the Earth. NASA calculates that the Earth obscures only about 4 square degrees out of 41,000 square degrees of the sky as seen from the Moon and this makes the Earth negligible as a shield for the Moon. Newer research suggests that the reason the side of the moon facing Earth has fewer impact craters is heat from Earth at the time when the Moon was formed, the lunar crust consists primarily of plagioclases formed when aluminium and calcium condensed and combined with silicates in the mantle
5.
Tidal locking
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Tidal locking occurs when, over the course of an orbit, there is no net transfer of angular momentum between an astronomical body and its gravitational partner. This state can result from the gradient between two co-orbiting bodies, acting over a sufficiently long period of time. In the case where the orbital eccentricity is zero, tidal locking results in one hemisphere of the revolving object constantly facing its partner. For example, the side of the Moon always faces the Earth. A tidally locked body in synchronous rotation takes just as long to rotate around its own axis as it does to revolve around its partner, usually, only the satellite is tidally locked to the larger body. However, if both the difference between the two bodies and the distance between them are relatively small, each may be tidally locked to the other, this is the case for Pluto. This effect is employed to stabilize some artificial satellites, the possibility of lifeforms existing on tidally-locked planets has been debated. The change in rotation rate necessary to lock a body B to a larger body A is caused by the torque applied by As gravity on bulges it has induced on B by tidal forces. These distortions are known as tidal bulges, when B is not yet tidally locked, the bulges travel over its surface, with one of the two high tidal bulges traveling close to the point where body A is overhead. Smaller bodies also experience distortion, but this distortion is less regular, the material of B exerts resistance to this periodic reshaping caused by the tidal force. In effect, some time is required to reshape B to the equilibrium shape. Seen from a point in space, the points of maximum bulge extension are displaced from the axis oriented toward A. Because the bulges are now displaced from the A–B axis, As gravitational pull on the mass in them exerts a torque on B. The torque on the A-facing bulge acts to bring Bs rotation in line with its period, whereas the back bulge. However, the bulge on the A-facing side is closer to A than the bulge by a distance of approximately Bs diameter. The net resulting torque from both bulges, then, is always in the direction that acts to synchronize Bs rotation with its orbital period and this results in a raising of Bs orbit about A in tandem with its rotational slowdown. For the other case where B starts off rotating too slowly, the tidal locking effect is also experienced by the larger body A, but at a slower rate because Bs gravitational effect is weaker due to Bs smaller mass. For example, Earths rotation is gradually being slowed by the Moon, current estimations are that this has helped lengthen the Earth day from about 6 hours to the current 24 hours
6.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
7.
Lunar phase
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The lunar phase or phase of the moon is the shape of the illuminated portion of the Moon as seen by an observer on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the positions of the Moon. The Moons rotation is locked by the Earths gravity, therefore the same lunar surface always faces Earth. This face is variously sunlit depending on the position of the Moon in its orbit, therefore, the portion of this hemisphere that is visible to an observer on Earth can vary from about 100% to 0%. The lunar terminator is the boundary between the illuminated and darkened hemispheres, each of the four intermediate lunar phases is roughly seven days but this varies slightly due to the elliptical shape of the Moons orbit. Aside from some craters near the lunar poles such as Shoemaker, all parts of the Moon see around 14.77 days of sunlight, in Western culture, the four principal lunar phases are new moon, first quarter, full moon, and third quarter. These are the instants when the Moons apparent geocentric celestial longitude minus the Suns apparent geocentric longitude is 0°, 90°, 180° and 270°. Each of these phases is instantaneous, lasting theoretically zero time, during the intervals between principal phases, the Moon appears either crescent-shaped or gibbous. These shapes, and the periods of time when the Moon shows them, are called the intermediate phases. They last, on average, one-quarter of a month, roughly 7.38 days, but their durations vary slightly because the Moons orbit is slightly elliptical. The descriptor waxing is used for a phase when the Moons apparent size is increasing, from new moon toward full moon. As the moon waxes, the lunar phases progress through new moon, crescent moon, first-quarter moon, gibbous moon, the moon is then said to wane as it passes through the gibbous moon, third-quarter moon, crescent moon and back to new moon. The terms old moon and new moon are not interchangeable, the old moon is a waning sliver until the moment it aligns with the sun and begins to wax, at which point it becomes new again. Half moon is used to mean the first- and third-quarter moons, while the term quarter refers to the extent of the moons cycle around the Earth. When a crescent Moon occurs, the phenomenon of earthshine may be apparent, in the Northern Hemisphere, if the left side of the Moon is dark then the light part is growing, and the Moon is referred to as waxing. If the right side of the Moon is dark then the part is shrinking. Assuming that the viewer is in the hemisphere, the right portion of the Moon is the part that is always growing. Nearer the Equator the Moon with its terminator will appear apparently horizontal during the morning and evening, the crescent Moon can open upward or downward, with the horns of the crescent pointing up or down, respectively
8.
Planetshine
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Planetshine is the illumination, by reflected sunlight from a planet, of part of the otherwise dark side of one of its moons. The best known example of planetshine is earthshine, which can be seen from Earth when the Moon is new, typically, this results in the side of the Moon opposite the Sun being bathed in a soft, faint light. Earthshine is reflected earthlight visible on Moons night side and it is also known as the Moons ashen glow or as the new Moon with the old Moon in her arm. Earthshine is most readily observable from shortly before until shortly after a new moon, when the Moon is new as viewed from Earth, Earth is nearly fully lit up as viewed from the Moon. Sunlight is reflected from the Earth to the side of the Moon. The night side appears to glow faintly and the orb of the Moon is dimly visible. Leonardo da Vinci explained the phenomenon in the early 16th century when he realized that both Earth and the Moon reflect sunlight at the same time, Light is reflected from the Earth to the Moon and back to the Earth as earthshine. Earthshine is used to determine the current albedo of the Earth. The data are used to analyze global cloud cover, a climate factor, oceans reflect the least amount of light, roughly 10%. Land reflects anywhere from 10–25% of the Suns light, and clouds reflect around 50%, so, the part of the Earth where it is daytime and from which the Moon is visible determines how bright the Moons earthshine appears at any given time. Studies of earthshine can be used to show how the Earths cloud cover varies over time, preliminary results show a 6. 5% dip in cloud cover between 1985 and 1997 and a corresponding increase between 1997 and 2003. This has implications for research, especially with regards to global warming. So while the Earths albedo is measurably increasing, the uncertainty over the amount of heat trapped means the effect on global temperature remains unclear. The Earth, Moon, and some other bodies have, to some extent, Light which strikes them is reflected preferentially back in the direction from which it has come, rather than in other directions. If the light comes from the Sun, it is reflected back toward the Sun, for example, when its phase is full, the Moon reflects light preferentially toward the Sun, and toward the Earth, which is in almost the same direction. The full Moon therefore appears brighter, when seen from Earth, the retroreflection is produced by spheres of transparent material on the reflecting surface. When it encounters a transparent sphere, light is reflected and refracted in a path, within the sphere. On the Earth, the spheres are droplets of water in clouds, on the Moon, large numbers of solid glassy spheres are found on the surface
9.
Orbit of the Moon
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Not to be confused with Lunar orbit. The Moon orbits Earth in the direction and completes one revolution relative to the stars in approximately 27.323 days. Earth and the Moon orbit about their barycentre, which lies about 4,600 km from Earths center, on average, the Moon is at a distance of about 385,000 km from Earths centre, which corresponds to about 60 Earth radii. With a mean velocity of 1.022 km/s, the Moon appears to move relative to the stars each hour by an amount roughly equal to its angular diameter. The Moon differs from most satellites of planets in that its orbit is close to the plane of the ecliptic. The plane of the orbit is inclined to the ecliptic by about 5°. The properties of the orbit described in this section are approximations, the Moons orbit around Earth has many irregularities, whose study has a long history. The orbit of the Moon is distinctly elliptical, with an eccentricity of 0.0549. The non-circular form of the lunar orbit causes variations in the Moons angular speed and apparent size as it moves towards, the mean angular movement relative to an imaginary observer at the barycentre is 13. 176° per day to the east. The Moons elongation is its angular distance east of the Sun at any time, at new moon, it is zero and the Moon is said to be in conjunction. At full moon, the elongation is 180° and it is said to be in opposition, in both cases, the Moon is in syzygy, that is, the Sun, Moon and Earth are nearly aligned. When elongation is either 90° or 270°, the Moon is said to be in quadrature, the orientation of the orbit is not fixed in space, but rotates over time. This orbital precession is also called apsidal precession and is the rotation of the Moons orbit within the orbital plane, the Moons apsidal precession is distinct from, and should not be confused with its axial precession. The mean inclination of the orbit to the ecliptic plane is 5. 145°. The rotational axis of the Moon is also not perpendicular to its plane, so the lunar equator is not in the plane of its orbit. Therefore, the angle between the ecliptic and the equator is always 1. 543°, even though the rotational axis of the Moon is not fixed with respect to the stars. The period from moonrise to moonrise at the poles is quite close to the sidereal period, when the sun is the furthest below the horizon, the moon will be full when it is at its highest point. The nodes are points at which the Moons orbit crosses the ecliptic, the Moon crosses the same node every 27.2122 days, an interval called the draconic or draconitic month
10.
Equator
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The Equator usually refers to an imaginary line on the Earths surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere. The Equator is about 40,075 kilometres long, some 78. 7% lies across water and 21. 3% over land, other planets and astronomical bodies have equators similarly defined. Generally, an equator is the intersection of the surface of a sphere with the plane that is perpendicular to the spheres axis of rotation. The latitude of the Earths equator is by definition 0° of arc, the equator is the only line of latitude which is also a great circle — that is, one whose plane passes through the center of the globe. The plane of Earths equator when projected outwards to the celestial sphere defines the celestial equator, in the cycle of Earths seasons, the plane of the equator passes through the Sun twice per year, at the March and September equinoxes. To an observer on the Earth, the Sun appears to travel North or South over the equator at these times, light rays from the center of the Sun are perpendicular to the surface of the Earth at the point of solar noon on the Equator. Locations on the Equator experience the quickest sunrises and sunsets because the sun moves nearly perpendicular to the horizon for most of the year. The Earth bulges slightly at the Equator, the diameter of the Earth is 12,750 kilometres. Because the Earth spins to the east, spacecraft must also launch to the east to take advantage of this Earth-boost of speed, seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earths axis relative to the plane of revolution. During the year the northern and southern hemispheres are inclined toward or away from the sun according to Earths position in its orbit, the hemisphere inclined toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter. At the equinoxes, the Earths axis is not tilted toward the sun, instead it is perpendicular to the sun meaning that the day is about 12 hours long, as is the night, across the whole of the Earth. Near the Equator there is distinction between summer, winter, autumn, or spring. The temperatures are usually high year-round—with the exception of high mountains in South America, the temperature at the Equator can plummet during rainstorms. In many tropical regions people identify two seasons, the wet season and the dry season, but many places close to the Equator are on the oceans or rainy throughout the year, the seasons can vary depending on elevation and proximity to an ocean. The Equator lies mostly on the three largest oceans, the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean. The highest point on the Equator is at the elevation of 4,690 metres, at 0°0′0″N 77°59′31″W and this is slightly above the snow line, and is the only place on the Equator where snow lies on the ground. At the Equator the snow line is around 1,000 metres lower than on Mount Everest, the Equator traverses the land of 11 countries, it also passes through two island nations, though without making a landfall in either. Starting at the Prime Meridian and heading eastwards, the Equator passes through, Despite its name, however, its island of Annobón is 155 km south of the Equator, and the rest of the country lies to the north
11.
Libration
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Lunar libration is distinct from the slight changes in the Moons visual size as seen from Earth. Although this appearance can also be described as a motion, libration is caused by actual changes in the physical distance of the Moon. The Moon generally has one hemisphere facing the Earth, due to tidal locking, therefore, humans first view of the far side of the Moon resulted from lunar exploration on October 7,1959. However, this picture is only approximately true, over time. Libration is manifested as a slow rocking back and forth of the Moon as viewed from Earth, libration in latitude results from a slight inclination between the Moons axis of rotation and the normal to the plane of its orbit around Earth. Its origin is analogous to how the seasons arise from Earths revolution about the Sun. In 1772 Lagranges analyses determined that small bodies can stably share the orbit as a planet if they remain near Lagrange points. Such ‘trojan asteroids’ have been found co-orbiting with Earth, Jupiter, Mars, trojan asteroids associated with Earth are difficult to observe in the visible spectrum, as their libration paths are such that they would be visible primarily in the daylight sky. In 2010, however, using infrared observation techniques, the asteroid 2010 TK7 was found to be a companion of the Earth, it librates around the leading Lagrange point, L4
12.
Northern Hemisphere
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The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined as being in the celestial hemisphere relative to the invariable plane of the solar system as Earths North pole. Due to the Earths axial tilt, winter in the Northern Hemisphere lasts from the December solstice to the March Equinox, the dates vary each year due to the difference between the calendar year and the astronomical year. Its surface is 60. 7% water, compared with 80. 9% water in the case of the Southern Hemisphere, the Arctic is the region north of the Arctic Circle. Its climate is characterized by cold winters and cool summers, precipitation mostly comes in the form of snow. The Arctic experiences some days in summer when the Sun never sets, the duration of these phases varies from one day for locations right on the Arctic Circle to several months near the North Pole, which is the middle of the Northern Hemisphere. Between the Arctic Circle and the Tropic of Cancer lies the Northern Temperate Zone, the changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather, tropical regions are generally hot all year round and tend to experience a rainy season during the summer months, and a dry season during the winter months. In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the coriolis effect, as a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres. These are best seen in circulation patterns in the North Atlantic. For the same reason, flows of air down toward the surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic of high pressure weather cells in the Northern Hemisphere, conversely, air rising from the northern surface of the Earth tends to draw air toward it in a counterclockwise pattern. Hurricanes and tropical storms spin counter-clockwise in the Northern Hemisphere, the shadow of a sundial moves clockwise in the Northern Hemisphere. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from the Southern Hemisphere, the North Pole faces away from the galactic center of the Milky Way. The Northern Hemisphere is home to approximately 6.57 billion people which is around 90% of the total human population of 7.3 billion people
13.
Giovanni Battista Riccioli
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Giovanni Battista Riccioli was an Italian astronomer and a Catholic priest in the Jesuit order. Riccioli was born in Ferrara, Italy and he entered the Society of Jesus on 6 October 1614. After completing his novitiate, he study of the humanities in 1616, pursuing those studies first at Ferrara. From 1620 to 1628 he studied philosophy and theology at the College of Parma, Parma Jesuits had developed a strong program of experimentation, such as with falling bodies. One of the most famous Italian Jesuits of the time, Giuseppe Biancani, was teaching at Parma when Riccioli arrived there, Riccioli mentions him with gratitude and admiration. By 1628 Ricciolis studies were complete and he requested missionary work, but that request was turned down. Instead he was assigned to teach at Parma, there he taught logic, physics, and metaphysics from 1629 to 1632, and engaged in some experiments with falling bodies and pendulums. In 1632 he became a member of a group charged with the formation of younger Jesuits and he spent the 1633-1634 academic year in Mantua, where he collaborated with Niccolo Cabeo in further pendulum studies. In 1635 he was back at Parma, where he taught theology, in 1636 he was sent to Bologna to serve as Professor of theology. Riccioli described himself as a theologian, but one with a strong and ongoing interest in astronomy since his student days and he said that many Jesuits were theologians, but few were astronomers. He said that once the enthusiasm for astronomy arose within him he could never extinguish it, eventually his superiors in the Jesuit order officially assigned him to the task of astronomical research. However, he continued to write on theology. Riccioli dealt not only with astronomy in his research, but also with physics, arithmetic, geometry, optics, gnomonics, geography and he was awarded a prize by Louis XIV in recognition of his activities and their relevance to contemporary culture. Riccioli continued to publish on both astronomy and theology up to his death and he died in Bologna at 73 years of age. One of Ricciolis most significant works was his 1651 Almagestum Novum, a work consisting of over 1500 folio pages densely packed with text, tables. Riccioli envisioned that the New Almagest would have three volumes, but only the first was completed, Riccioli is credited with being the first person to precisely measure the acceleration due to gravity of falling bodies. Books 2 and 9 of the New Almagest Riccioli included a significant discussion of and extensive experimental reports on the motions of falling bodies and he was interested in the pendulum as a device for precisely measuring time. He also reported that a pendulums period increases if the amplitude of its swing is increased to 40 degrees and he sought to develop a pendulum whose period was precisely one second – such a pendulum would complete 86,400 swings in a 24-hour period
14.
Francesco Maria Grimaldi
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Francesco Maria Grimaldi was an Italian Jesuit priest, mathematician and physicist who taught at the Jesuit college in Bologna. He was born in Bologna to Paride Grimaldi and Anna Cattani, between 1640 and 1650, working with Riccioli, he investigated the free fall of objects, confirming that the distance of fall was proportional to the square of the time taken. Grimaldi and Riccioli also made a calculation of the gravitational constant by recording the oscillations of an accurate pendulum. C and he was the first to make accurate observations on the diffraction of light, and coined the word diffraction. Through experimentation he was able to demonstrate that the passage of light could not be reconciled with the idea that it moved in a rectilinear path. Rather, the light passed through the hole took on the shape of a cone. Later physicists used his work as evidence that light was a wave and he also discovered what are known as diffraction bands. The crater Grimaldi on the Moon is named after him, physicomathesis de lumine, coloribus, et iride, aliisque annexis List of Jesuit scientists List of Roman Catholic scientist-clerics Catholic Encyclopedia article for Francesco Maria Grimaldi. Grimaldis Physico-mathesis de lumine - digital facsimile from the Linda Hall Library
15.
Lunar Reconnaissance Orbiter
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The Lunar Reconnaissance Orbiter is a NASA robotic spacecraft currently orbiting the Moon in an eccentric polar mapping orbit. Data collected by LRO has been described as essential for planning NASAs future human and its detailed mapping program is identifying safe landing sites, locating potential resources on the Moon, characterizing the radiation environment, and demonstrating new technologies. LRO and LCROSS were launched as part of the United Statess Vision for Space Exploration program, the probe has made a 3-D map of the Moons surface at 100-meter resolution and 98. 2% coverage, including 0. 5-meter resolution images of Apollo landing sites. The first images from LRO were published on July 2,2009, the total cost of the mission is reported as US$583 million, of which $504 million pertains to the main LRO probe and $79 million to the LCROSS satellite. Developed at NASAs Goddard Space Flight Center, LRO is a large and its mission duration was planned for one year, but has since been extended numerous times after review by NASA. After completing a design review in February 2006 and a critical design review in November 2006. Launch was planned for October 2008, but this slid to April as the spacecraft underwent testing in a vacuum chamber. Launch was rescheduled for June 17,2009, because of the delay in a priority military launch, the one-day delay was to allow the Space Shuttle Endeavour a chance to lift off for mission STS-127 following a hydrogen fuel leak that canceled an earlier planned launch. In addition, LRO has provided some of the first images and precise locations of landers and equipment from previous American and Russian lunar missions, Diviner The Diviner Lunar Radiometer Experiment measures lunar surface thermal emission to provide information for future surface operations and exploration. LEND The Lunar Exploration Neutron Detector provides measurements, creates maps, LOLA The Lunar Orbiter Laser Altimeter investigation provides a precise global lunar topographic model and geodetic grid. LROC The Lunar Reconnaissance Orbiter Camera addresses the measurement requirements of landing site certification, LROC comprises a pair of narrow-angle push-broom imaging cameras and a single wide-angle camera. The mission is returning approximately 70–100 terabytes of image data and it is expected that this photography will boost public acknowledgement of the validity of the landings, and further discredit Apollo conspiracy theories. Mini-RF The Miniature Radio Frequency radar demonstrated new lightweight SAR and communications technologies, prior to the LROs launch, NASA gave members of the public the opportunity to have their names placed in a microchip on the LRO. The deadline for this opportunity was July 31,2008, about 1.6 million names were submitted. On June 23,2009, the Lunar Reconnaissance Orbiter entered into orbit around the Moon after a journey from the Earth. When launched, the spacecraft was aimed at a point ahead of the Moons position, a mid-course correction was required during the trip in order for the spacecraft to correctly enter Lunar orbit. Once the spacecraft reached the far side of the Moon, its motor was fired in order for it to be captured by the Moons gravity into an elliptical lunar orbit. A series of four rocket burns over the four days put the satellite into its commissioning phase orbit where each instrument was brought online
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Geography
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Geography is a field of science devoted to the study of the lands, the features, the inhabitants, and the phenomena of Earth. The first person to use the word γεωγραφία was Eratosthenes, Geography is an all-encompassing discipline that seeks an understanding of the Earth and its human and natural complexities—not merely where objects are, but how they have changed and come to be. It is often defined in terms of the two branches of geography and physical geography. Geography has been called the world discipline and the bridge between the human and the physical sciences, Geography is a systematic study of the Earth and its features. Traditionally, geography has been associated with cartography and place names, although many geographers are trained in toponymy and cartology, this is not their main preoccupation. Geographers study the space and the temporal database distribution of phenomena, processes, because space and place affect a variety of topics, such as economics, health, climate, plants and animals, geography is highly interdisciplinary. The interdisciplinary nature of the approach depends on an attentiveness to the relationship between physical and human phenomena and its spatial patterns. Names of places. are not geography. know by heart a whole gazetteer full of them would not, in itself and this is a description of the world—that is Geography. In a word Geography is a Science—a thing not of mere names but of argument and reason, of cause, just as all phenomena exist in time and thus have a history, they also exist in space and have a geography. Geography as a discipline can be split broadly into two main fields, human geography and physical geography. The former largely focuses on the environment and how humans create, view, manage. The latter examines the environment, and how organisms, climate, soil, water. The difference between these led to a third field, environmental geography, which combines physical and human geography. Physical geography focuses on geography as an Earth science and it aims to understand the physical problems and the issues of lithosphere, hydrosphere, atmosphere, pedosphere, and global flora and fauna patterns. Physical geography can be divided into broad categories, including, Human geography is a branch of geography that focuses on the study of patterns. It encompasses the human, political, cultural, social, and it requires an understanding of the traditional aspects of physical and human geography, as well as the ways that human societies conceptualize the environment. Integrated geography has emerged as a bridge between the human and the geography, as a result of the increasing specialisation of the two sub-fields. Examples of areas of research in the environmental geography include, emergency management, environmental management, sustainability, geomatics is concerned with the application of computers to the traditional spatial techniques used in cartography and topography
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Astronomy
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Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets, while the phenomena include supernovae explosions, gamma ray bursts, more generally, all astronomical phenomena that originate outside Earths atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole, Astronomy is the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, during the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the results and observations being used to confirm theoretical results. Astronomy is one of the few sciences where amateurs can play an active role, especially in the discovery. Amateur astronomers have made and contributed to many important astronomical discoveries, Astronomy means law of the stars. Astronomy should not be confused with astrology, the system which claims that human affairs are correlated with the positions of celestial objects. Although the two share a common origin, they are now entirely distinct. Generally, either the term astronomy or astrophysics may be used to refer to this subject, however, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics. Few fields, such as astrometry, are purely astronomy rather than also astrophysics, some titles of the leading scientific journals in this field includeThe Astronomical Journal, The Astrophysical Journal and Astronomy and Astrophysics. In early times, astronomy only comprised the observation and predictions of the motions of objects visible to the naked eye, in some locations, early cultures assembled massive artifacts that possibly had some astronomical purpose. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye, most of early astronomy actually consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon, the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the model of the Universe, or the Ptolemaic system. The Babylonians discovered that lunar eclipses recurred in a cycle known as a saros
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Latitude
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In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earths surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles, lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the location of features on the surface of the Earth. Without qualification the term latitude should be taken to be the latitude as defined in the following sections. Also defined are six auxiliary latitudes which are used in special applications, there is a separate article on the History of latitude measurements. Two levels of abstraction are employed in the definition of latitude and longitude, in the first step the physical surface is modelled by the geoid, a surface which approximates the mean sea level over the oceans and its continuation under the land masses. The second step is to approximate the geoid by a mathematically simpler reference surface, the simplest choice for the reference surface is a sphere, but the geoid is more accurately modelled by an ellipsoid. The definitions of latitude and longitude on such surfaces are detailed in the following sections. Lines of constant latitude and longitude together constitute a graticule on the reference surface, latitude and longitude together with some specification of height constitute a geographic coordinate system as defined in the specification of the ISO19111 standard. This is of importance in accurate applications, such as a Global Positioning System, but in common usage, where high accuracy is not required. In English texts the latitude angle, defined below, is denoted by the Greek lower-case letter phi. It is measured in degrees, minutes and seconds or decimal degrees, the precise measurement of latitude requires an understanding of the gravitational field of the Earth, either to set up theodolites or to determine GPS satellite orbits. The study of the figure of the Earth together with its field is the science of geodesy. These topics are not discussed in this article and this article relates to coordinate systems for the Earth, it may be extended to cover the Moon, planets and other celestial objects by a simple change of nomenclature. The primary reference points are the poles where the axis of rotation of the Earth intersects the reference surface, the plane through the centre of the Earth and perpendicular to the rotation axis intersects the surface at a great circle called the Equator. Planes parallel to the plane intersect the surface in circles of constant latitude. The Equator has a latitude of 0°, the North Pole has a latitude of 90° North, the latitude of an arbitrary point is the angle between the equatorial plane and the radius to that point. The latitude, as defined in this way for the sphere, is termed the spherical latitude
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Zenith
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The zenith is an imaginary point directly above a particular location, on the imaginary celestial sphere. Above means in the direction opposite to the apparent gravitational force at that location. The opposite direction, i. e. the direction in which gravity pulls, is toward the nadir, the zenith is the highest point on the celestial sphere. It was reduced to samt and miswritten as senit/cenit, as the m was misread as an ni, through the Old French cenith, zenith first appeared in the 17th century. The term zenith is sometimes used to refer to the highest point, way or level reached by a celestial body during its apparent orbit around a given point of observation. This sense of the word is used to describe the location of the Sun, but to an astronomer the sun does not have its own zenith. In a scientific context, the zenith is the direction of reference for measuring the zenith angle, in astronomy, the altitude in the horizontal coordinate system and the zenith angle are complementary angles, with the horizon perpendicular to the zenith. The astronomical meridian is also determined by the zenith, and is defined as a circle on the sphere that passes through the zenith, nadir. A zenith telescope is a type of telescope designed to point straight up at or near the zenith, the NASA Orbital Debris Observatory and the Large Zenith Telescope are both zenith telescopes since the use of liquid mirrors meant these telescopes could only point straight up. Azimuth Geodesy History of geodesy Keyhole problem Midheaven Subsolar point Vertical deflection Horizontal coordinate system Glickman, Todd S. Glossary of meteorology
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Oceanus Procellarum
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Oceanus Procellarum is a vast lunar mare on the western edge of the near side of the Moon. Like all lunar maria, Oceanus Procellarum was formed by ancient basaltic flood volcanic eruptions that covered the region in a thick, unlike the other lunar maria, however, Oceanus Procellarum may or may not be contained within a single well-defined impact basin. Around its edges lie many minor bays and seas, including Mare Nubium, to the northeast, Oceanus Procellarum is separated from Mare Imbrium by the Carpathian Mountains. On its north-west edge lies the 32 km wide Aristarchus ray crater, also, the more-prominent ray-crater Copernicus lies within the eastern edge of the mare, distinctly with its bright ray materials sprawling over the darker material. On the northern edge of Oceanus Procellarum lies Sinus Roris, there are several hypotheses about the origin of Oceanus Procellarum and a related asymmetry between the near and far sides of the Moon. One of the most likely is that Procellarum was a result of an ancient giant impact on the side of the Moon. The size of the basin has been estimated to be more than 3,000 kilometers. The impact likely happened very early in the Moons history, at the time when magma ocean still existed or just ceased to exist and it deposited 5–30 km of crustal material on the far side forming highlands. If this is the case, all impact related structures such as crater rim, central peak etc. have been obliterated by later impacts, one piece of evidence in support of this hypothesis is concentration of incompatible elements and low calcium pyroxene around Oceanus Procellarum. Procellarum may have also formed by spatially inhomogeneous heating during the Moons formation. Other hypotheses include a late accretion of a companion Moon on the far side, the latter postulates that in addition to the present Moon, another smaller moon was formed from debris of the giant impact. After a few tens of millions of years it collided with the Moon, the robotic lunar probes Luna 9, Luna 13, Surveyor 1 and Surveyor 3 landed in Oceanus Procellarum. Luna 9 landed southwest of Galilaei crater in 1966, Luna 13 landed southeast of Seleucus crater, later in 1966. Surveyor 1 landed north of Flamsteed crater in 1966, and Surveyor 3 landed in 1967, the manned Apollo 12 mission also landed in Oceanus Procellarum, with astronauts Pete Conrad and Alan Bean on board. Their landing site, within 300m of Surveyor 3, has known as Mare Cognitum
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Rift valley
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A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault. A rift valley is formed on a divergent plate boundary, an extension, a spreading apart of the surface. When the tensional forces were enough to cause the plate to split apart. The drop of the center creates the nearly parallel steeply dipping walls of a valley when it is new. One of the best known examples of process is the East African Rift. On Earth, rifts can occur at all elevations, from the sea floor to plateaus and they are often associated with a number of adjoining subsidiary or co-extensive valleys, which are typically considered part of the principal rift valley geologically. The most extensive rift valley is located along the crest of the ridge system and is the result of sea floor spreading. Examples of this type of include the Mid-Atlantic Ridge and the East Pacific Rise. In these instances, not only the crust, but also entire tectonic plates, are in the process of breaking apart to create new plates, if they continue, continental rifts will eventually become oceanic rifts. Other rift valleys are the result of bends or discontinuities in horizontally-moving faults, when these bends or discontinuities are in the same direction as the relative motions along the fault, extension occurs. For example, for a right lateral-moving fault, a bend to the right will result in stretching, in the view of many geologists today, the Dead Sea lies in a rift which results from a leftward discontinuity in the left lateral-moving Dead Sea Transform fault. Where a fault breaks into two strands, or two faults run close to other, crustal extension may also occur between them, as a result of differences in their motions. Both types of fault-caused extension commonly occur on a small scale, many of the worlds largest lakes are located in rift valleys. Lake Baikal in Siberia, a World Heritage Site, lies in a rift valley. Baikal is both the deepest lake in the world and, with 20% of all of the freshwater on earth, has the greatest volume. Lake Tanganyika, second by both measures, is in the Albertine Rift, the westernmost arm of the active East African Rift, Lake Superior in North America, the largest freshwater lake by area, lies in the ancient and dormant Midcontinent Rift. The largest subglacial lake, Lake Vostok, may lie in an ancient rift valley. Lake Nipissing and Lake Timiskaming in Ontario and Quebec, Canada lie inside a valley called the Ottawa-Bonnechere Graben
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Gravity Recovery and Interior Laboratory
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The two small spacecraft GRAIL A and GRAIL B were launched on 10 September 2011 aboard a single launch vehicle, the most-powerful configuration of a Delta II, the 7920H-10. GRAIL A separated from the rocket about nine minutes after launch and they arrived at their orbits around the Moon 25 hours apart. The first probe entered orbit on 31 December 2011 and the second followed on 1 January 2012, the two spacecraft impacted the Lunar surface on December 17,2012. Maria Zuber of the Massachusetts Institute of Technology is GRAILs principal investigator, nASAs Jet Propulsion Laboratory manages the project. As of August 5,2011, the program has cost US$496 million, upon launch the spacecraft were named GRAIL A and GRAIL B and a contest was opened to school children to select names. Nearly 900 classrooms from 45 states, Puerto Rico and the District of Columbia, the winning names, Ebb and Flow, were suggested by 4th grade students at Emily Dickinson Elementary School in Bozeman, Montana. Each spacecraft transmitted and received telemetry from the spacecraft and Earth-based facilities. By measuring the change in distance between the two spacecraft, the gravity field and geological structure of the Moon was obtained, the two spacecraft were able to detect very small changes in the distance between one another. Changes in distance as small as one micron were detectable and measurable, the gravitational field of the Moon was mapped in unprecedented detail. A second phase, at an altitude, of data collection began 31 Aug 2012. On 5 Dec 2012 NASA released a gravity map of the Moon made from GRAIL data, the knowledge acquired will aid understanding of the evolutionary history of the terrestrial planets and computations of lunar orbits. Ka band Lunar Gravity Ranging System, derived from the Gravity Recovery, 90% of the GRACE software was reused for GRAIL. Radio science beacon Moon Knowledge Acquired by Middle school students, each MoonKAM system consists of a digital video controller and four camera heads. Click here for a MoonKAM photo from lunar orbit, thrusters aboard each spacecraft were capable of producing 22 newtons. The propulsion subsystem consisted of a fuel tank and a Re-repressurization system which were activated shortly after lunar orbit insertion. The very tight tolerances in the plan left little room for error correction leading to a launch window lasting one second. The primary science phase of GRAIL lasted for 88 days, from 7 Mar 2012 to 29 May 2012 and it was followed by a second science phase starting on 8 Aug. The gravity mapping technique was similar to that used by Gravity Recovery and Climate Experiment, the orbital insertion dates were December 31,2011 and January 1,2012
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Lunar mare
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The lunar maria /ˈmɑːriə/ are large, dark, basaltic plains on Earths Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for seas, by astronomers who mistook them for actual seas. They are less reflective than the highlands as a result of their iron-rich compositions, the maria cover about 16 percent of the lunar surface, mostly on the side visible from Earth. The few maria on the far side are smaller, residing mostly in very large craters. The traditional nomenclature for the Moon also includes one oceanus, as well as features with the names lacus, palus, the last three are smaller than maria, but have the same nature and characteristics. The names of maria generally refer to states of mind, with a few exceptions, for example, Mare Humboldtianum and Mare Smythii were established long before the nomenclature was accepted and do not follow this pattern. The ages of the mare basalts have been determined both by direct radiometric dating and by the technique of crater counting, the few basaltic eruptions that occurred on the far side are old, whereas the youngest flows are found within Oceanus Procellarum on the nearside. While many of the basalts either erupted within, or flowed into, low-lying impact basins, there are many common misconceptions concerning the spatial distribution of mare basalts. Since many mare basalts fill low-lying impact basins, it was assumed that the impact event itself somehow caused the volcanic eruption. It is sometimes suggested that the gravity field of the Earth might preferentially allow eruptions to occur on the near side, but not far side. However, in a frame rotating with the Moon, the centrifugal acceleration the moon is experiencing is exactly equal. There is thus no net force directed towards the Earth, the Earth tides do act to deform the shape of the Moon, but this shape is one of an elongated ellipsoid with high points at both the sub- and anti-Earth points. As an analogy, one should remember that there are two high tides per day on Earth, and not one, since mare basaltic magmas are denser than upper crustal anorthositic materials, basaltic eruptions might be favored at locations of low elevation where the crust is thin. However, the far side South Pole-Aitken basin contains the lowest elevations of the Moon and is yet only modestly filled by basaltic lavas, in addition, the crustal thickness beneath this basin is predicted to be much smaller than beneath Oceanus Procellarum. It is commonly suggested that there is form of link between the synchronous rotation of the Moon about the Earth, and the mare basalts. However, gravitational torques that result in tidal despinning only arise from the moments of inertia of the body, furthermore, tidal despinning is predicted to have occurred quickly, whereas the majority of mare basalts erupted about one billion years later. The reason that the basalts are predominantly located on the near-side hemisphere of the Moon is still being debated by the scientific community. In this low-impact collision, the moon was crushed into the surface of the moon
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Man in the Moon
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The Man in the Moon refers to any of several pareidolic images of a human face, head or body that certain traditions recognise in the disc of the full moon. The images are composed of the areas of the lunar maria, or seas. One older European tradition sees a figure of a man carrying a burden on his back. He is sometimes seen as accompanied by a small dog, various cultures recognise other examples of lunar pareidolia, such as the Moon rabbit. This particular human face can also be seen in tropical regions on both sides of the equator, however, the moon orientation associated with the face is observed less frequently—and eventually not at all—as one moves towards the South Pole. Conventionalized illustrations of the Man in the Moon seen in Western art often show a very simple face in the moon, or a human profile in the crescent moon. The Man in the Moon can also refer to a character said to live on or in the moon. An example is Yue-Laou, from Chinese tradition, There are various explanations for how the Man in the Moon came to be. A longstanding European tradition holds that the man was banished to the moon for some crime, Christian lore commonly held that he is the man caught gathering sticks on the Sabbath and sentenced by God to death by stoning in the book of Numbers XV. 32-36. Some Germanic cultures thought he was a man stealing from a neighbors hedgerow to repair his own. There is a Roman legend that he is a sheep-thief, one medieval Christian tradition claims him as Cain, the Wanderer, forever doomed to circle the Earth. John Lyly says in the prologue to his Endymion, There liveth none under the sunne, in Norse mythology, Máni is the male personification of the moon who crosses the sky in a horse-drawn carriage. He is continually pursued by the Great Wolf Hati who catches him at Ragnarök, the name Máni simply means Moon. In Chinese mythology, the goddess Change is stranded upon the moon after foolishly consuming a double dose of an immortality potion and she is accompanied by a small group of moon rabbits. In Haida mythology, the figure represents a boy gathering sticks, the boys father had told him the moons light would brighten the night, allowing the chore to be completed. Not wanting to gather sticks, the boy complained and ridiculed the moon, as punishment for his disrespect, the boy was taken from earth and trapped on the moon. There is a belief that the Man in the Moon enjoyed drinking. An old ballad runs, In the English Middle Ages and renaissance, the moon was held to be the god of drunkards, the man in the moon is named in an early dated English nursery rhyme, The Man in the Moon is made up of various lunar maria
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Geology of the Moon
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The geology of the Moon is quite different from that of Earth. The complex geomorphology of the surface has been formed by a combination of processes, especially impact cratering. The Moon is a body, with a crust, mantle. Geological studies of the Moon are based on a combination of Earth-based telescope observations, measurements from orbiting spacecraft, lunar samples, and geophysical data. Six locations were sampled directly during the manned Apollo program landings from 1969 to 1972, in addition, three robotic Soviet Luna spacecraft returned another 326 grams from 1970 to 1976. The Moon is the only body for which we have samples with a known geologic context. A handful of lunar meteorites have been recognized on Earth, though their source craters on the Moon are unknown, a substantial portion of the lunar surface has not been explored, and a number of geological questions remain unanswered. Elements known to be present on the surface include, among others, oxygen, silicon, iron, magnesium, calcium, aluminium, manganese. Among the more abundant are oxygen, iron and silicon, the oxygen content is estimated at 45%. Carbon and nitrogen appear to be present only in quantities from deposition by solar wind. Neutron spectrometry data from Lunar Prospector indicate the presence of hydrogen concentrated at the poles, for a long period of time, the fundamental question regarding the history of the Moon was of its origin. Early hypotheses included fission from Earth, capture, and co-accretion, today, the giant impact hypothesis is widely accepted by the scientific community. The geological history of the Moon has been defined into six major epochs, starting about 4.5 billion years ago, the newly formed Moon was in a molten state and was orbiting much closer to Earth resulting in tidal forces. These tidal forces deformed the molten body into an ellipsoid, with the major axis pointed towards Earth, the first important event in the geologic evolution of the Moon was the crystallization of the near global magma ocean. It is not known with certainty what its depth was, the first minerals to form in this ocean were the iron and magnesium silicates olivine and pyroxene. Because these minerals were denser than the material around them. After crystallization was about 75% complete, less dense anorthositic plagioclase feldspar crystallized and floated, forming an anorthositic crust about 50 km in thickness. The oldest of the Mg-suite rocks have ages of about 3.85 Ga. However
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Giant-impact hypothesis
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The colliding body is sometimes called Theia, from the name of the mythical Greek Titan who was the mother of Selene, the goddess of the Moon. Analysis of lunar rocks, published in 2016, suggests that the impact may have been a direct hit, the giant-impact hypothesis is currently the favoured scientific hypothesis for the formation of the Moon. Supporting evidence includes, Earths spin and the Moons orbit have similar orientations, Moon samples indicate that the Moons surface was once molten. The Moon has a small iron core. The Moon has a lower density than Earth, evidence exists of similar collisions in other star systems. Giant collisions are consistent with the theories of the formation of the solar system. The stable-isotope ratios of lunar and terrestrial rock are identical, implying a common origin, there remain several questions concerning the best current models of the giant-impact hypothesis, however. However, as of 2015 there is no self-consistent model that starts with the giant-impact event, other remaining questions include when the Moon lost its share of volatile elements and why Venus—which experienced giant impacts during its formation—does not host a similar moon. In 1898, George Darwin made the suggestion that the Earth, Darwins hypothesis was that a molten Moon had been spun from the Earth because of centrifugal forces, and this became the dominant academic explanation. Using Newtonian mechanics, he calculated that the Moon had orbited much more closely in the past and was drifting away from the Earth and this drifting was later confirmed by American and Soviet experiments, using laser ranging targets placed on the Moon. Nonetheless, Darwins calculations could not resolve the mechanics required to trace the Moon backward to the surface of the Earth. In 1946, Reginald Aldworth Daly of Harvard University challenged Darwins explanation and their models suggested that, at the end of the planet formation period, several satellite-sized bodies had formed that could collide with the planets or be captured. They proposed that one of objects may have collided with the Earth, ejecting refractory. This collision could potentially explain the unique geological and geochemical properties of the Moon and it is hypothesized that most of the outer silicates of the colliding body would be vaporized, whereas a metallic core would not. Hence, most of the material sent into orbit would consist of silicates. The more volatile materials that were emitted during the collision probably would escape the Solar System, the name of the hypothesized protoplanet is derived from the mythical Greek titan Theia /ˈθiːə/, who gave birth to the Moon goddess Selene. This designation was proposed initially by the English geochemist Alex N. Halliday in 2000 and has accepted in the scientific community. According to modern theories of formation, Theia was part of a population of Mars-sized bodies that existed in the Solar System 4.5 billion years ago
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Lunar south pole
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The lunar south pole is of special interest to scientists because of the postulated occurrence of water ice in permanently shadowed areas around it. Of the lunar poles, the pole is of greater interest because the area that remains in shadow is much larger than that at the north pole. The lunar south pole craters are unique in that sunlight does not reach the bottom, such craters are cold traps that contain a fossil record of the early solar system. The rotational axis of the Moon lies within Shackleton Crater, notable craters nearest to the lunar south pole include De Gerlache, Sverdrup, Shoemaker, Faustini, Haworth, Nobile and Cabeus. Spacecraft from several countries have explored the region around the south pole. Extensive studies were conducted by the Lunar Orbiter, Clementine, Lunar Prospector, Lunar Reconnaissance Orbiter, Kaguya, nASAs LCROSS mission found a significant amount of water in Cabeus. Future planned exploration of the Lunar south polar region includes a mission by Shackleton Energy Company. Lunar Mission One is a British-led, unmanned Moon mission announced in November 2014 and it will attempt to land on the lunar south pole, then drill down at least 20m and possibly as deep as 100m. This could dramatically improve the understanding of the Moons composition, its history and formation. The mission is attempting to gain crowdfunding on Kickstarter, colonization of the Moon polar regions Selenography Face on Moon South Pole Lunar north pole USGS, Earths Moon
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Internal structure of the Moon
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Having a mean density of 3,346.4 kg/m³, the Moon is a differentiated body, being composed of a geochemically distinct crust, mantle, and core. This structure is believed to have resulted from the crystallization of a magma ocean shortly after its formation about 4.5 billion years ago. Crystallization of this magma ocean would have given rise to a mafic mantle, geochemical mapping from orbit implies that the crust of the Moon is largely anorthositic in composition, consistent with the magma ocean hypothesis. Based on geophysical techniques, the crust is estimated to be on average about 50 km thick, partial melting within the mantle of the Moon gave rise to the eruption of mare basalts on the lunar surface. Some lunar basalts contain high abundances of titanium, suggesting that the mantle is highly heterogeneous in composition, moonquakes have been found to occur deep within the mantle of the Moon about 1,000 km below the surface. These occur with monthly periodicities and are related to stresses caused by the eccentric orbit of the Moon about the Earth. A few shallow moonquakes with hypocenters located about 100 km below the surface have also been detected, several lines of evidence imply that the lunar core is small, with a radius of about 350 km or less. The size of the core is only about 20% the size of the Moon itself. The composition of the core is not well constrained, but most believe that it is composed of metallic iron alloyed with a small amount of sulfur. Analyses of the Moons time-variable rotation indicate that the core is at least partly molten. In 2010, a reanalysis of the old Apollo seismic data on the deep moonquakes using modern processing methods confirmed that the Moon has a rich core with a radius of 330 ±20 km. The same reanalysis established that the inner core made of pure iron has the radius of 240 ±10 km. The core is surrounded by the melted layer of the lower mantle with a radius of 480 ±20 km. These results imply that 40% of the core by volume has solidified, the density of the liquid outer core is about 5 g/cm3 and it could contain as much 6% sulfur by weight. The temperature in the core is probably about 1600–1700 K. Structure of the Earth Moon articles in Planetary Science Research Discoveries, including articles about internal structure of the Moon
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Atmosphere of the Moon
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The atmosphere of the Moon is a very scant presence of gases surrounding the Moon. For most practical purposes, the Moon is considered to be surrounded by vacuum, the pressure of this small mass is around 3×10−15 atm, varying throughout the day, and in total weighs less than 10 metric tonnes. One source of the atmosphere is outgassing, the release of gases such as radon and helium resulting from radioactive decay within the crust. Another important source is the bombardment of the surface by micrometeorites, the solar wind. What little atmosphere the Moon has consists of some gases, including sodium and potassium. At sea level on Earth, each cubic centimeter of the atmosphere contains approximately 1019 molecules, on Earth, this is considered to be a very good vacuum. In fact, the density of the atmosphere at the Moons surface is comparable to the density of the outermost fringes of Earths atmosphere, where the International Space Station orbits. Argon-40, helium-4, oxygen and/or methane, nitrogen and/or carbon monoxide, the Moon may also have a tenuous atmosphere of electrostatically-levitated dust. See Moon dust for more details
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Gravitation of the Moon
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The acceleration due to gravity on the surface of the Moon is about 1.625 m/s2, about 16. 6% that on Earths surface or 0.16 ɡ. Over the entire surface, the variation in gravitational acceleration is about 0.0253 m/s2, because weight is directly dependent upon gravitational acceleration, things on the Moon will weigh only 16. 6% of what they weigh on the Earth. The gravitational field of the Moon has been measured by tracking the signals emitted by orbiting spacecraft. Since the gravitational field of the Moon affects the orbit of a spacecraft, a major feature of the Moons gravitational field is the presence of mascons, which are large positive gravity anomalies associated with some of the giant impact basins. These anomalies significantly influence the orbit of spacecraft around the Moon, and they were initially discovered by the analysis of Lunar Orbiter tracking data, navigation tests prior to the Apollo program showed positioning errors much larger than mission specifications. Mascons are in due to the presence of dense mare basaltic lava flows that fill some of the impact basins. However, lava flows by themselves cannot fully explain the gravitational variations, based on Lunar Prospector gravitational models, it has been suggested that some mascons exist that do not show evidence for mare basaltic volcanism. The huge expanse of mare basaltic volcanism associated with Oceanus Procellarum does not cause a positive gravity anomaly, the center of gravity of the Moon does not coincide exactly with its geometric center, but is displaced toward the Earth by about 2 kilometers. Magnetic field of the Moon Micro-g environment
31.
Hill sphere
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An astronomical bodys Hill sphere is the region in which it dominates the attraction of satellites. The outer shell of that constitutes a zero-velocity surface. To be retained by a planet, a moon must have an orbit that lies within the planets Hill sphere and that moon would, in turn, have a Hill sphere of its own. Any object within that distance would tend to become a satellite of the moon, one simple view of the extent of the Solar System is the Hill sphere of the Sun with respect to local stars and the galactic nucleus. In more precise terms, the Hill sphere approximates the gravitational sphere of influence of a body in the face of perturbations from a more massive body. It was defined by the American astronomer George William Hill, based on the work of the French astronomer Édouard Roche, for this reason, it is also known as the Roche sphere. In the example to the right, the Hill sphere extends between the Lagrangian points L1 and L2, which lie along the line of centers of the two bodies. The region of influence of the body is shortest in that direction. When eccentricity is negligible, this becomes r ≈ a m 3 M3, in the Earth example, the Earth orbits the Sun at a distance of 149.6 million km. The Hill sphere for Earth thus extends out to about 1.5 million km, all stable satellites of the Earth must have an orbital period shorter than seven months. The previous formula can be re-stated as follows,3 r 3 a 3 ≈ m M and this is also convenient, because many planetary astronomers work in and remember distances in units of planetary radii. The Hill sphere is only an approximation, and other forces can eventually perturb an object out of the sphere and this third object should also be of small enough mass that it introduces no additional complications through its own gravity. The region of stability for retrograde orbits at a distance from the primary, is larger than the region for prograde orbits at a large distance from the primary. This was thought to explain the preponderance of retrograde moons around Jupiter, however, a sphere of this size and mass would be denser than lead. In fact, in any low Earth orbit, a body must be more dense than lead in order to fit inside its own Hill sphere. A spherical geostationary satellite, however, would only need to be more than 6% of the density of water to support satellites of its own. Within the Solar System, the planet with the largest Hill radius is Neptune, with 116 million km, or 0.775 au, an asteroid from the asteroid belt will have a Hill sphere that can reach 220000 km, diminishing rapidly with decreasing mass. The Hill sphere of 1999 KW4, a Mercury-crosser asteroid that has a moon, a typical extrasolar hot Jupiter, HD209458 b, has a Hill sphere radius of 593,000 km, about 8 times its physical radius of approx 71,000 km
32.
Magnetic field of the Moon
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The magnetic field of the Moon is very weak in comparison to that of the Earth. Other major differences are that the Moon does not currently have a magnetic field. One hypothesis holds that the crustal magnetizations were acquired early in history when a geodynamo was still operating. The small size of the core, however, is a potential obstacle to promoting that hypothesis to the status of theory. Alternatively, it is possible that on a body such as the Moon. In support of this, it has noted that the largest crustal magnetizations appear to be located near the antipodes of the giant impact basins. It has been proposed such a phenomenon could result from the free expansion of an impact-generated plasma cloud around the Moon in the presence of an ambient magnetic field. For example, the Chandrayaan-1 spacecraft mapped a mini-magnetosphere at the Crisium antipode on the far side. The mini-magnetosphere is 360 km across at the surface and is surrounded by a 300-km-thick region of enhanced plasma flux that results from the wind flowing around the mini-magnetosphere. Theres growing evidence that fine particles of moondust might actually float and this could create a temporary nighttime atmosphere of dust. The moondust atmosphere might also gather itself into a sort of diaphanous wind, drawn by differences in global charge accumulation, floating dust would naturally fly from the strongly negative nightside to the weakly negative dayside. This dust storm effect would be strongest at the Moons terminator, much of these details are still speculative, but the Lunar Prospector spacecraft detected changes in the lunar nightside voltage during magnetotail crossings, jumping from -200 V to -1000 V. Further characterization was done by the Lunar Atmosphere and Dust Environment Explorer orbiter in late 2013, in the Space Odyssey series by Arthur C. Clarke, a monolith is found on the Moon near the crater Tycho by its unnaturally powerful magnetic field, gravity field of the Moon Topography of the Moon
33.
Sodium tail of the Moon
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The Moon has been shown to have a tail of sodium atoms too faint to be detected by the human eye. It is hundreds of thousands of long, and was discovered in 1998 as a result of scientists from Boston University observing the Leonid meteor storm. The 1998 Leonid meteor shower temporarily tripled the mass of the tail by adding to the population of atoms being outgassed by the Moon. The daily impact of small meteoroids produces a constant tail on the Moon, Atmosphere of the Moon Lunar Atmosphere and Dust Environment Explorer Radiation pressure Moons tail spotted. Astronomers discover that moon has long, comet-like tail
34.
Moonlight
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Moonlight is the light that reaches Earth from the Moon, consisting mostly of sunlight, with some starlight and earthlight reflected from those portions of its surface which the Suns light strikes. The intensity of moonlight varies greatly depending on the lunar cycle, when the Moon is nearest to Earth and viewed at high altitude at tropical latitudes, the illuminance can reach 0.32 lux. The full Moon is about 1,000,000 times fainter than the Sun, the color of moonlight, particularly near full Moon, appears bluish to the human eye compared to most artificial light sources. This is because of the Purkinje effect - the light is not actually tinted blue, the Moons albedo is 0.136, meaning only 13. 6% of sunlight incident on the Moon is reflected. Moonlight generally hampers astronomical viewing, so astronomers usually avoid making observations near full Moon and it takes approximately 1.26 seconds for the moonlight to hit the Earths surface. In folklore, moonlight sometimes has a harmful influence, for example, sleeping in the light of a full Moon on certain nights was said to transform a person into a werewolf. The light of the Moon was thought to worsen the symptoms of lunatics, nyctalopia was thought to be caused by sleeping in moonlight in the tropics. Moon blindness is a name for equine recurrent uveitis and it is no longer thought to be caused by moonlight. In the 16th century, moonmilk, a white limestone precipitate found in caves, was thought to be caused by the rays of the moon. Airglow Daylight Diffuse reflection Earthlight Scotobiology Starlight Phases of the Moon at USNO Strange Moonlight at Science@NASA Moonlight Brightness at LunarLight Photography
35.
Earthlight (astronomy)
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Earthlight is the partial illumination of the dark portion of the moons surface by light reflected from the Earth and from the Earths airglow. It is also known as Earthshine, the Moons ashen glow and this phenomenon is best observed from just after new moon, when the moon is a thin crescent. On these nights it is easy to see the disk of the moon. The word is rare but is recognised by the Oxford English Dictionary and it would also be a suitable term for an observer on the moon seeing the Earth during the lunar night, or from an astronaut of the window inside a spacecraft. Arthur C. Clarke uses it in this sense in his novel Earthlight, sunlight Moonlight Starlight List of light sources Media related to Earthshine at Wikimedia Commons
36.
Orbital elements
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Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in classical two-body systems. There are many different ways to describe the same orbit. A real orbit changes over time due to perturbations by other objects. A Keplerian orbit is merely an idealized, mathematical approximation at a particular time, the traditional orbital elements are the six Keplerian elements, after Johannes Kepler and his laws of planetary motion. When viewed from a frame, two orbiting bodies trace out distinct trajectories. Each of these trajectories has its focus at the center of mass. When viewed from a non-inertial frame centred on one of the bodies, only the trajectory of the body is apparent. An orbit has two sets of Keplerian elements depending on which body is used as the point of reference, the reference body is called the primary, the other body is called the secondary. The primary does not necessarily possess more mass than the secondary, and even when the bodies are of equal mass, the orbital elements depend on the choice of the primary. The main two elements that define the shape and size of the ellipse, Eccentricity —shape of the ellipse, semimajor axis —the sum of the periapsis and apoapsis distances divided by two. For circular orbits, the axis is the distance between the centers of the bodies, not the distance of the bodies from the center of mass. For paraboles or hyperboles, this is infinite, tilt angle is measured perpendicular to line of intersection between orbital plane and reference plane. Any three points on an ellipse will define the ellipse orbital plane, the plane and the ellipse are both two-dimensional objects defined in three-dimensional space. Longitude of the ascending node —horizontally orients the ascending node of the ellipse with respect to the reference frames vernal point, and finally, Argument of periapsis defines the orientation of the ellipse in the orbital plane, as an angle measured from the ascending node to the periapsis. True anomaly at epoch defines the position of the body along the ellipse at a specific time. The mean anomaly is a mathematically convenient angle which varies linearly with time and it can be converted into the true anomaly ν, which does represent the real geometric angle in the plane of the ellipse, between periapsis and the position of the orbiting object at any given time. Thus, the anomaly is shown as the red angle ν in the diagram
37.
Lunar distance (astronomy)
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Lunar distance is as a unit of measure in astronomy. It is the distance from the center of Earth to the center of the Moon. More technically, it is the mean semi-major axis of the lunar orbit. It may also refer to the distance between the centers of the Earth and the Moon, or less commonly, the instantaneous Earth-Moon distance. The lunar distance is approximately a quarter of a million miles, Lunar distance is also called Earth-Moon distance, Earth–Moon characteristic distance, or distance to the Moon, and commonly indicated with LD or Δ ⊕ L. The mean semi-major axis has a value of 384,402 km, the time-averaged distance between Earth and Moon centers is 385,000.6 km. The actual distance varies over the course of the orbit of the Moon, from 356,500 km at the perigee to 406,700 km at apogee, Lunar distance is commonly used to express the distance to near-Earth object encounters. The measurement is useful in characterizing the lunar radius, the mass of the Sun. Millimeter-precision measurements of the distance are made by measuring the time taken for light to travel between LIDAR stations on the Earth and retroreflectors placed on the Moon. The Moon is spiraling away from the Earth at a rate of 3.8 cm per year. By coincidence, the diameter of corner cubes in retroreflectors on the Moon is also 3.8 cm, the instantaneous lunar distance is constantly changing. In fact the distance between the Moon and Earth can change by as much as 75 m/s, or more than 1,000 kilometers in just 6 hours. There are other effects that influence the lunar distance. Some factors are described in this section, the distance to the Moon can be measured to an accuracy of 2 mm over a 1-hour sampling period, which results in an overall uncertainty of 2–3 cm for the average distance. However, due to its orbit with varying eccentricity, the instantaneous distance varies with monthly periodicity. Furthermore, the distance is perturbed by the effects of various astronomical bodies - most significantly the Sun. Other forces responsible for minuscule perturbations are other planets in the system, asteroids, tidal forces. The effect of pressure from the sun contributes an amount of ±3.6 mm to the lunar distance
38.
Apsis
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An apsis is an extreme point in an objects orbit. The word comes via Latin from Greek and is cognate with apse, for elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- and ap-, or apo- added to a reference to the thing being orbited. For a body orbiting the Sun, the point of least distance is the perihelion, the terms become periastron and apastron when discussing orbits around other stars. For any satellite of Earth including the Moon the point of least distance is the perigee, for objects in Lunar orbit, the point of least distance is the pericynthion and the greatest distance the apocynthion. For any orbits around a center of mass, there are the terms pericenter and apocenter, periapsis and apoapsis are equivalent alternatives. A straight line connecting the pericenter and apocenter is the line of apsides and this is the major axis of the ellipse, its greatest diameter. For a two-body system the center of mass of the lies on this line at one of the two foci of the ellipse. When one body is larger than the other it may be taken to be at this focus. Historically, in systems, apsides were measured from the center of the Earth. In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body. However, in the case of spacecraft, the family of terms are used to refer to the orbital altitude of the spacecraft from the surface of the central body. The arithmetic mean of the two limiting distances is the length of the axis a. The geometric mean of the two distances is the length of the semi-minor axis b, the geometric mean of the two limiting speeds is −2 ε = μ a which is the speed of a body in a circular orbit whose radius is a. The words pericenter and apocenter are often seen, although periapsis/apoapsis are preferred in technical usage, various related terms are used for other celestial objects. The -gee, -helion and -astron and -galacticon forms are used in the astronomical literature when referring to the Earth, Sun, stars. The suffix -jove is occasionally used for Jupiter, while -saturnium has very rarely used in the last 50 years for Saturn. The -gee form is used as a generic closest approach to planet term instead of specifically applying to the Earth. During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon, regarding black holes, the term peri/apomelasma was used by physicist Geoffrey A. Landis in 1998 before peri/aponigricon appeared in the scientific literature in 2002
39.
Lunar node
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The lunar nodes are the orbital nodes of the Moon, that is, the points where the orbit of the Moon crosses the ecliptic. The ascending or north node is where the crosses from south of the ecliptic to north of the ecliptic. The descending or south node is where it crosses north of the ecliptic to south of the ecliptic. Eclipses occur only near the nodes, Solar eclipses occur when the passage of the Moon through a node coincides with the new moon. A lunar eclipse may occur if there is a full moon within 11°38, of a node, and a solar eclipse may occur if there is a new moon within 17°25 of a node. The plane of the orbit precesses in space and hence the lunar nodes precess around the ecliptic. The same cycle, measured against an inertial frame of reference such as ICRS is 18.599525 years, the two solar eclipses in July 2000 were around the time that the moon was at its ascending node. Ascending-node eclipses recur after one year on average, which is about 0.94901 Gregorian years. The nodes are called by different names in different areas of the world, in ancient European texts, it is referred to as the dragons head. The symbol of the node is, the astronomical and astrological symbol for the Dragons head. Similarly the descending node is the point where the Moon is descending from the North hemisphere to South hemisphere and it is also known as the dragons tail, and its symbol is the inversion of that of the ascending node. Note that the so-called North node may in fact lie South of the South node in the course of the nodal cycle, in Hindu astronomy, the ascending node ☊ is called Rahu and the descending node ☋ is called Ketu. In Tibetan Astrology the southern node is named Kalagni, the lunar orbit is inclined by about 5.1 degrees to the ecliptic, hence the Moon can be up to about 5 degrees north or south of the ecliptic. The ecliptic is inclined by about 23. 4° to the celestial equator, furthermore, occultations by the Moon of the star group the Pleiades, which are over 4° North of the ecliptic, occur during a comparatively brief period once every nodal period. In Western astrology the ascending and descending nodes are known as the North Node. Only the north node is marked in horoscopes, as the south node is by definition at the opposite point in the chart. In Vedic astrology, the north and south nodes are called Rahu and Ketu respectively, Astrology Eclipse Horoscope Lunar standstill Orbit of the Moon Natal chart Sun and Moon Polar Applet, showing moonrise/moonset azimuths Astronomy Answers, What are the standstills of the Moon. Eclipses, Cosmic Clockwork of the Ancients Lunar and solar periods, about inertial frame of reference for measuring movements of celestial bodies
40.
Lunar precession
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Precession is the change in direction of an axis of rotation with respect to a reference plane. The orbit of the Moon has two important such precessional motions, the first precession is movement of the plane of the lunar orbit. The period of the lunar nodal precession is defined as the time it takes the ascending node to move through 360 degrees relative to the vernal equinox. It is about 18.6 years and the direction of motion is westward and this is the reason that a draconic month or nodal period is shorter than the sidereal month. After one nodal precession period, the number of draconic months exceeds the number of months by exactly one. This period is about 6,793 days, as a result of this nodal precession, the time for the Sun to return to the same lunar node, the eclipse year, is about 18.6377 days shorter than a sidereal year. The number of solar orbits during one lunar nodal precession period equals the period of divided by this difference. 365. 25/18.6377 -1 The second precession is that of the axis of the Moons elliptical orbit. This is the reason that a month is longer than the sidereal month. This apsidal precession completes one rotation in the time as the number of sidereal months exceeds the number of anomalistic months by exactly one. Lunar theory Orbit of the Moon Explanatory Supplement to the Astronomical Almanac, seidelmann, US Naval Observatory / University Science Books, pp.114,115, p.701
41.
Syzygy (astronomy)
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In astronomy, a syzygy is a straight-line configuration of three celestial bodies in a gravitational system. The word is used in reference to the Sun, Earth, and either the Moon or a planet. Solar and lunar eclipses occur at times of syzygy, as do transits, the term is often applied when the Sun and Moon are in conjunction or opposition. The word syzygy is often used to describe interesting configurations of planets in general. For example, one such case occurred on March 21,1894 around 23,00 GMT, when Mercury transited the Sun, and Mercury and Venus both simultaneously transited the Sun as seen from Saturn. It is also used to describe situations when all the planets are on the side of the Sun although they are not necessarily in a straight line. On June 3,2014, the Curiosity rover on Mars observed the planet Mercury transiting the Sun, syzygy sometimes results in an occultation, transit, or eclipse. An occultation occurs when a larger body passes in front of an apparently smaller one. A transit occurs when a smaller body passes in front of a larger one, in the combined case where the smaller body regularly transits the larger, an occultation is also termed a secondary eclipse. An eclipse occurs when a body totally or partially disappears from view, either by an occultation, as with an eclipse, or by passing into the shadow of another body. Transits and occultations of the Sun by Earths Moon are called solar eclipses regardless of whether the Sun is completely or partially covered, the term eclipse is also used more generally for bodies passing in front of one another. For example, a NASA Astronomy Picture of the Day refers to the Moon eclipsing and occulting Saturn interchangeably, syzygy causes the bimonthly phenomena of spring and neap tides. At the new and full moon, the Sun and Moon are in syzygy and their tidal forces act to reinforce each other, and the ocean both rises higher and falls lower than the average. Conversely, at the first and third quarter, the Sun and Moon are at angles, their tidal forces counteract each other. Tidal variation can also be measured in the earths crust, and this may affect the frequency of earthquakes
42.
New moon
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In astronomy, new moon is the first phase of the Moon, when it orbits not seen from the Earth, the moment when the Moon and the Sun have the same ecliptical longitude. The Moon is not visible at this time except when it is seen in silhouette during a solar eclipse when it is illuminated by earthshine, see the article on phases of the Moon for further details. A lunation or synodic month is the time from one new moon to the next. In the J2000.0 epoch, the length of a lunation is 29.530588 days. However, the length of any one month can vary from 29.26 to 29.80 days due to the perturbing effects of the Suns gravity on the Moons eccentric orbit. In a lunar calendar, each corresponds to a lunation. Each lunar cycle can be assigned a unique Lunation Number to identify it, the length of a lunation is about 29.53 days. Its precise duration is linked to many phenomena in nature, such as the variation between spring and neap tides, an approximate formula to compute the mean moments of new moon for successive months is, d =5.597661 +29. For all new moons between 1601 and 2401, the difference is 0.592 days = 14h13m in either direction. The duration of a lunation varies in this period between 29.272 and 29.833 days, i. e. −0. 259d = 6h12m shorter, or +0. 302d = 7h15m longer than average. This range is smaller than the difference between mean and true conjunction, because during one lunation the periodic terms cannot all change to their maximum opposite value, see the article on the full moon cycle for a fairly simple method to compute the moment of new moon more accurately. These are now outdated, Chapront et al. published improved parameters, quadratic term, In ELP2000–85, D has a quadratic term of −5. 8681T2, expressed in lunations N, this yields a correction of +87. 403×10–12N2 days to the time of conjunction. The term includes a contribution of 0. 5×. The most current estimate from Lunar Laser Ranging for the acceleration is, therefore, the new quadratic term of D is = -6. 8498T2. Indeed, the polynomial provided by Chapront et alii provides the same value and this translates to a correction of +14. 622×10−12N2 days to the time of conjunction, the quadratic term now is, +102. 026×10−12N2 days. For UT, analysis of historical observations shows that ΔT has an increase of +31 s/cy2. Converted to days and lunations, the correction from ET to UT becomes, the theoretical tidal contribution to ΔT is about +42 s/cy2 the smaller observed value is thought to be mostly due to changes in the shape of the Earth. Because the discrepancy is not fully explained, uncertainty of our prediction of UT may be as large as the difference between these values,11 s/cy2
43.
Full moon
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A full moon is the lunar phase that occurs when the Moon is completely illuminated as seen from Earth. This occurs when Earth is located directly between the Sun and the Moon and this means that the hemisphere of the Moon that is facing Earth is almost fully illuminated by the Sun and appears round. On some occasions at the time of full moon there is also a lunar eclipse so the face appears reddish due to the rayleigh scattering of blue light in Earths atmosphere. Lunar eclipses can occur only at full moon, where the Moons orbit allows it to pass through Earths shadow, Lunar eclipses do not occur every month because the Moon usually passes above or below Earths shadow. Lunar eclipses can only when the full moon occurs near the two nodes of the orbit, either the ascending or descending node. This causes eclipses to occur about every 6 months. The time interval between similar lunar phases—the synodic month—averages about 29.53 days, therefore, in those lunar calendars in which each month begins on the new moon, the full moon falls on either the 14th or 15th of the lunar month. Because calendar months have a number of days, lunar months may be either 29 or 30 days long. A full moon is thought of as an event of a full nights duration. This is somewhat misleading because the Moon seen from Earth is continuously becoming larger and/or smaller and its absolute maximum size occurs at the moment expansion has stopped. For any given location, about half of these absolute maximum full moons will be visible, as the other half occur during the day. Many almanacs list full moons not just by date, but by their time as well. Typical monthly calendars that include phases of the Moon may be offset by one day if intended for use in a different time zone, Full moons are generally a poor time to conduct astronomical observations, because the bright reflected sunlight from the Moon overwhelms the dimmer light from stars. On 12 December 2008, the moon occurred closer to the Earth than it had been at any time for the previous 15 years. On 19 March 2011, another full moon occurred, closer to the Earth than at any time for the previous ~18 years. On 14 November 2016, a full moon occurred closer to the Earth than at any time for the previous 68 years. The true time of a full moon may differ from this approximation by up to about 14.5 hours as a result of the non-circularity of the moons orbit, see New moon for an explanation of the formula and its parameters. The age and apparent size of the full moon vary in a cycle of just under 14 synodic months, Full moons are traditionally associated with temporal insomnia, insanity and various magical phenomena such as lycanthropy
44.
Eclipse
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An eclipse occurs during a syzygy. The term eclipse is most often used to either a solar eclipse, when the Moons shadow crosses the Earths surface, or a lunar eclipse. A binary star system can also produce eclipses if the plane of the orbit of its constituent stars intersects the observers position, for any two objects in space, a line can be extended from the first through the second. The latter object will block some amount of light being emitted by the former, as viewed from such a location, this shadowing event is known as an eclipse. Typically the cross-section of the involved in an astronomical eclipse are roughly disk shaped. The region of an objects shadow during an eclipse is divided into three parts, The umbra, within which the object completely covers the light source, for the Sun, this light source is the photosphere. The antumbra, extending beyond the tip of the umbra, within which the object is completely in front of the light source, the penumbra, within which the object is only partially in front of the light source. A total eclipse occurs when the observer is within the umbra, an annular eclipse when the observer is within the antumbra, during a lunar eclipse only the umbra and penumbra are applicable. This is because Earths apparent diameter from the viewpoint of the Moon is nearly four times that of the Sun, the same terms may be used analogously in describing other eclipses, e. g. the antumbra of Deimos crossing Mars, or Phobos entering Marss penumbra. For Earth, on average L is equal to 1. 384×106 km, hence the umbral cone of the Earth can completely envelop the Moon during a lunar eclipse. If the occulting object has an atmosphere, however, some of the luminosity of the star can be refracted into the volume of the umbra. This occurs, for example, during an eclipse of the Moon by the Earth—producing a faint, on Earth, the shadow cast during an eclipse moves very approximately at 1 km per sec. This depends on the location of the shadow on the Earth, http, //www. sciforums. com/threads/speed-of-eclipse-shadow. 53722/ An eclipse cycle takes place when a series of eclipses are separated by a certain interval of time. This happens when the orbital motions of the bodies form repeating harmonic patterns, a particular instance is the saros, which results in a repetition of a solar or lunar eclipse every 6,585.3 days, or a little over 18 years. Because this is not a number of days, successive eclipses will be visible from different parts of the world. An eclipse involving the Sun, Earth, and Moon can occur only when they are nearly in a line, allowing one to be hidden behind another. Because the orbital plane of the Moon is tilted with respect to the plane of the Earth. The Sun, Earth and nodes are aligned twice a year, there can be from four to seven eclipses in a calendar year, which repeat according to various eclipse cycles, such as a saros
45.
Lunar eclipse
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A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra. This can occur only when the sun, Earth, and moon are aligned exactly, or very closely so, hence, a lunar eclipse can occur only the night of a full moon. The type and length of an eclipse depend upon the Moons location relative to its orbital nodes, a total lunar eclipse has the direct sunlight completely blocked by the earths shadow. The only light seen is refracted through the earths shadow and this light looks red for the same reason that the sunset looks red, due to rayleigh scattering of the more blue light. Because of its color, a total lunar eclipse is sometimes called a blood moon. Unlike a solar eclipse, which can be viewed only from a relatively small area of the world. A lunar eclipse lasts for a few hours, whereas a total eclipse lasts for only a few minutes at any given place. Also unlike solar eclipses, lunar eclipses are safe to view without any eye protection or special precautions, for the date of the next eclipse see the section Recent and forthcoming lunar eclipses. The shadow of the Earth can be divided into two parts, the umbra and penumbra. Within the umbra, there is no solar radiation. However, as a result of the Suns large angular size, solar illumination is only partially blocked in the portion of the Earths shadow. A penumbral eclipse occurs when the moon passes through the Earths penumbra, the penumbra causes a subtle darkening of the moons surface. A special type of eclipse is a total penumbral eclipse. Total penumbral eclipses are rare, and when these occur, that portion of the moon which is closest to the umbra can appear darker than the rest of the moon. A partial lunar eclipse occurs when only a portion of the moon enters the umbra, when the moon travels completely into the Earths umbra, one observes a total lunar eclipse. The moons speed through the shadow is about one kilometer per second, nevertheless, the total time between the moons first and last contact with the shadow is much longer and could last up to four hours. The relative distance of the moon from the Earth at the time of an eclipse can affect the eclipses duration, in particular, when the moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest. The diameter of the umbra does not decrease appreciably within the changes in the distance of the moon
46.
Total penumbral lunar eclipse
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A total penumbral eclipse is a lunar eclipse that occurs when the moon becomes completely immersed in the penumbral cone of the Earth without touching the umbra. It is a path for the moon to pass within the penumbra. It can happen on the Earths northern or southern penumbral edges, in addition, the size of the penumbra is sometimes too small where the moon enters it to contain the moon. The majority of the time, the size of the moon, such eclipses constitute a relatively small fraction of lunar eclipses, and the distribution of these events is uneven, occurring between 0 and 9 times per century. The period of variation is about 600 years and also correlates with the frequency of total umbral eclipses. The maximum number in Freds 5K canon https, //eclipse. gsfc. nasa. gov/LEcat5/LEcatalog. html is 8, for saros 19 see https, Saros 58,95, and 114 have 6. 114 is the saros in the canon to have a total of 7 total penumbral lunar eclipses that are NOT all in a row. Source, https, //www. iau. org/administration/membership/individual/6886/ Lists of lunar eclipses Moon
