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.
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
3.
Lunar craters
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Lunar craters are impact craters on Earths Moon. The Moons surface has many craters, almost all of which were formed by impacts, the word crater was adopted by Galileo from the Greek word for vessel -. Galileo built his first telescope in late 1609, and turned it to the Moon for the first time on November 30,1609. He discovered that, contrary to general opinion at that time, the Moon was not a perfect sphere, scientific opinion as to the origin of craters swung back and forth over the ensuing centuries. The formation of new craters is studied in the lunar impact monitoring program at NASA, the biggest recorded creation was caused by an impact recorded on March 17,2013. Visible to the eye, the impact is believed to be from an approximately 40 kg meteoroid striking the surface at a speed of 90,000 km/h. Because of the Moons lack of water, and atmosphere, or tectonic plates, there is little erosion, the age of large craters is determined by the number of smaller craters contained within it, older craters generally accumulating more small, contained craters. The smallest craters found have been microscopic in size, found in rocks returned to Earth from the Moon, the largest crater called such is about 290 kilometres across in diameter, located near the lunar South Pole. However, it is believed many of the lunar maria were formed by giant impacts. In 1978, Chuck Wood and Leif Andersson of the Lunar & Planetary Lab devised a system of categorization of lunar impact craters and they used a sampling of craters that were relatively unmodified by subsequent impacts, then grouped the results into five broad categories. These successfully accounted for about 99% of all lunar impact craters, the LPC Crater Types were as follows, ALC — small, cup-shaped craters with a diameter of about 10 km or less, and no central floor. The archetype for this category is Albategnius C, BIO — similar to an ALC, but with small, flat floors. Typical diameter is about 15 km, the lunar crater archetype is Biot. SOS — the interior floor is wide and flat, with no central peak, the inner walls are not terraced. The diameter is normally in the range of 15–25 km, TRI — these complex craters are large enough so that their inner walls have slumped to the floor. They can range in size from 15–50 km in diameter, TYC — these are larger than 50 km, with terraced inner walls and relatively flat floors. They frequently have large central peak formations, tycho is the archetype for this class. Beyond a couple of hundred kilometers diameter, the peak of the TYC class disappear
4.
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
5.
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
6.
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
7.
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
8.
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
9.
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
10.
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
