1.
Sculptor Dwarf Galaxy
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The Sculptor Dwarf Galaxy is a dwarf spheroidal galaxy that is a satellite of the Milky Way. The galaxy lies within the constellation Sculptor and it was discovered in 1937 by American astronomer Harlow Shapley using the 24-inch Bruce refractor at Boyden Observatory. The galaxy is located about 290,000 light-years away from the Solar System, the Sculptor Dwarf contains only 4 percent of the carbon and other heavy elements in our own galaxy, the Milky Way, making it similar to primitive galaxies seen at the edge of the universe. The metallicity of Sculptor dwarf appears to be broken up two distinct groups, one with = -2.3 and the other with = -1.5. Similar to many of the other Local Group galaxies, the older metal-poor segment appears more extended than the younger metal-rich segment, the Sculptor Dwarf Galaxy on WikiSky, DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
2.
Sculptor Dwarf Irregular Galaxy
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The Sculptor Dwarf Irregular Galaxy is an irregular galaxy in the constellation Sculptor. The galaxy was discovered in 1976, the Sculptor Dwarf Irregular Galaxy and the dwarf galaxy UGCA442 are both companions of the spiral galaxy NGC7793. These galaxies all lie within the Sculptor Group, a weakly bound, Sculptor Dwarf Galaxy – a dwarf spheroidal or elliptical galaxy, also in Sculptor, but significantly closer, a satellite of the Milky Way. The Sculptor Dwarf Irregular Galaxy on WikiSky, DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
3.
Constellation
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A constellation is formally defined as a region of the celestial sphere, with boundaries laid down by the International Astronomical Union. The constellation areas mostly had their origins in Western-traditional patterns of stars from which the constellations take their names, in 1922, the International Astronomical Union officially recognized the 88 modern constellations, which cover the entire sky. They began as the 48 classical Greek constellations laid down by Ptolemy in the Almagest, Constellations in the far southern sky are late 16th- and mid 18th-century constructions. 12 of the 88 constellations compose the zodiac signs, though the positions of the constellations only loosely match the dates assigned to them in astrology. The term constellation can refer to the stars within the boundaries of that constellation. Notable groupings of stars that do not form a constellation are called asterisms, when astronomers say something is “in” a given constellation they mean it is within those official boundaries. Any given point in a coordinate system can unambiguously be assigned to a single constellation. Many astronomical naming systems give the constellation in which an object is found along with a designation in order to convey a rough idea in which part of the sky it is located. For example, the Flamsteed designation for bright stars consists of a number, the word constellation seems to come from the Late Latin term cōnstellātiō, which can be translated as set of stars, and came into use in English during the 14th century. It also denotes 88 named groups of stars in the shape of stellar-patterns, the Ancient Greek word for constellation was ἄστρον. Colloquial usage does not draw a distinction between constellation in the sense of an asterism and constellation in the sense of an area surrounding an asterism. The modern system of constellations used in astronomy employs the latter concept, the term circumpolar constellation is used for any constellation that, from a particular latitude on Earth, never sets below the horizon. From the North Pole or South Pole, all constellations south or north of the equator are circumpolar constellations. In the equatorial or temperate latitudes, the term equatorial constellation has sometimes been used for constellations that lie to the opposite the circumpolar constellations. They generally include all constellations that intersect the celestial equator or part of the zodiac, usually the only thing the stars in a constellation have in common is that they appear near each other in the sky when viewed from the Earth. In galactic space, the stars of a constellation usually lie at a variety of distances, since stars also travel on their own orbits through the Milky Way, the star patterns of the constellations change slowly over time. After tens to hundreds of thousands of years, their familiar outlines will become unrecognisable, the terms chosen for the constellation themselves, together with the appearance of a constellation, may reveal where and when its constellation makers lived. The earliest direct evidence for the constellations comes from inscribed stones and it seems that the bulk of the Mesopotamian constellations were created within a relatively short interval from around 1300 to 1000 BC
4.
Sculptor (constellation)
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Sculptor is a small and faint constellation in the southern sky. It was introduced by Nicolas Louis de Lacaille in the 18th century and he originally named it Apparatus Sculptoris, but the name was later shortened. The region to the south of Cetus and Aquarius had been named by Aratus in 270 BCE as The Waters – an area of scattered faint stars with two brighter stars standing out, professor of astronomy Bradley Schaefer has proposed that these stars were most likely Alpha and Delta Sculptoris. He named all but one in honour of instruments that symbolised the Age of Enlightenment, Sculptor is a small constellation bordered by Aquarius and Cetus to the north, Fornax to the east, Phoenix to the south, Grus to the southwest, and Piscis Austrinus to the west. The bright star Fomalhaut is nearby, the three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is Scl. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 6 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 23h 06. 4m and 01h 45. 5m, while the coordinates are between −24. 80° and −39. 37°. The whole constellation is visible to observers south of latitude 50°N, no stars brighter than 3rd magnitude are located in Sculptor. This is explained by the fact that Sculptor contains the south pole where stellar density is very low. Overall, there are 52 stars within the constellations borders brighter than or equal to apparent magnitude 6.5, the brightest star is Alpha Sculptoris, an SX Arietis-type variable star with a spectral type B7IIIp and an apparent magnitude of 4.3. It is 780 ±30 light-years distant from Earth, R Sculptoris is a red giant that has been found to be surrounded by spirals of matter likely ejected around 1800 years ago. The constellation also contains the Sculptor Dwarf, a galaxy which is a member of the Local Group, as well as the Sculptor Group. The Sculptor Galaxy, a spiral galaxy and the largest member of the group. Another prominent member of the group is the irregular galaxy NGC55, one unique galaxy in Sculptor is the Cartwheel Galaxy, at a distance of 500 million light-years. The result of a merger around 300 million years ago, the Cartwheel Galaxy has a core of older, yellow stars, and a ring of younger, blue stars. The smaller galaxy in the collision is now incorporated into the core, the shock waves from the collision sparked extensive star formation in the outer ring. Sculptor was a United States Navy Crater class cargo ship named after the constellation, notes Citations Sources Sculptor Constellation at Constellation Guide
5.
Right ascension
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Right ascension is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question. When combined with declination, these astronomical coordinates specify the direction of a point on the sphere in the equatorial coordinate system. Right ascension is the equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a direction on an equator. Right ascension is measured continuously in a circle from that equinox towards the east. Any units of measure could have been chosen for right ascension, but it is customarily measured in hours, minutes. Astronomers have chosen this unit to measure right ascension because they measure a stars location by timing its passage through the highest point in the sky as the Earth rotates. The highest point in the sky, called meridian, is the projection of a line onto the celestial sphere. A full circle, measured in units, contains 24 × 60 × 60 = 86 400s, or 24 × 60 = 1 440m. Because right ascensions are measured in hours, they can be used to time the positions of objects in the sky. For example, if a star with RA = 01h 30m 00s is on the meridian, sidereal hour angle, used in celestial navigation, is similar to right ascension, but increases westward rather than eastward. Usually measured in degrees, it is the complement of right ascension with respect to 24h and it is important not to confuse sidereal hour angle with the astronomical concept of hour angle, which measures angular distance of an object westward from the local meridian. The Earths axis rotates slowly westward about the poles of the ecliptic and this effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates are inherently relative to the year of their observation, coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. The right ascension of Polaris is increasing quickly, the North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18h and 6h respectively. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC. But Hipparchus and his successors made their star catalogs in ecliptic coordinates, the easiest way to do that is to use an equatorial mount, which allows the telescope to be aligned with one of its two pivots parallel to the Earths axis
6.
Declination
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In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declinations angle is measured north or south of the celestial equator, the root of the word declination means a bending away or a bending down. It comes from the root as the words incline and recline. Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere, points north of the celestial equator have positive declinations, while those south have negative declinations. Any units of measure can be used for declination, but it is customarily measured in the degrees, minutes. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere, the Earths axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, therefore, equatorial coordinates are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch. Coordinates from different epochs must be rotated to match each other. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity. This similarly occurs in the Southern Hemisphere for objects with less than −90° − φ. An extreme example is the star which has a declination near to +90°. Circumpolar stars never dip below the horizon, conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earths surface. Generally, if a star whose declination is δ is circumpolar for some observer, then a star whose declination is −δ never rises above the horizon, as seen by the same observer. Likewise, if a star is circumpolar for an observer at latitude φ, neglecting atmospheric refraction, declination is always 0° at east and west points of the horizon. At the north point, it is 90° − |φ|, and at the south point, from the poles, declination is uniform around the entire horizon, approximately 0°. Non-circumpolar stars are visible only during certain days or seasons of the year, the Suns declination varies with the seasons. As seen from arctic or antarctic latitudes, the Sun is circumpolar near the summer solstice, leading to the phenomenon of it being above the horizon at midnight
7.
Redshift
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In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum. Some redshifts are an example of the Doppler effect, familiar in the change of apparent pitches of sirens, a redshift occurs whenever a light source moves away from an observer. Finally, gravitational redshift is an effect observed in electromagnetic radiation moving out of gravitational fields. However, redshift is a common term and sometimes blueshift is referred to as negative redshift. Knowledge of redshifts and blueshifts has been applied to develop several terrestrial technologies such as Doppler radar and radar guns, Redshifts are also seen in the spectroscopic observations of astronomical objects. Its value is represented by the letter z, a special relativistic redshift formula can be used to calculate the redshift of a nearby object when spacetime is flat. However, in contexts, such as black holes and Big Bang cosmology. Special relativistic, gravitational, and cosmological redshifts can be understood under the umbrella of frame transformation laws, the history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect. The effect is named after Christian Doppler, who offered the first known physical explanation for the phenomenon in 1842, the hypothesis was tested and confirmed for sound waves by the Dutch scientist Christophorus Buys Ballot in 1845. Doppler correctly predicted that the phenomenon should apply to all waves, before this was verified, however, it was found that stellar colors were primarily due to a stars temperature, not motion. Only later was Doppler vindicated by verified redshift observations, the first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is called the Doppler–Fizeau effect. In 1868, British astronomer William Huggins was the first to determine the velocity of a moving away from the Earth by this method. In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red. In 1887, Vogel and Scheiner discovered the annual Doppler effect, in 1901, Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors. The word does not appear unhyphenated until about 1934 by Willem de Sitter, perhaps indicating that up to point its German equivalent. Beginning with observations in 1912, Vesto Slipher discovered that most spiral galaxies, Slipher first reports on his measurement in the inaugural volume of the Lowell Observatory Bulletin. Three years later, he wrote a review in the journal Popular Astronomy, Slipher reported the velocities for 15 spiral nebulae spread across the entire celestial sphere, all but three having observable positive velocities
8.
Radial velocity
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The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the velocity is the component of the objects velocity that points in the direction of the radius connecting the object. In astronomy, the point is taken to be the observer on Earth. In astronomy, radial velocity is measured to the first order of approximation by Doppler spectroscopy. The quantity obtained by this method may be called the barycentric radial-velocity measure or spectroscopic radial velocity, by contrast, astrometric radial velocity is determined by astrometric observations. A positive radial velocity indicates the distance between the objects is or was increasing, a radial velocity indicates the distance between the source and observer is or was decreasing. In many binary stars, the orbital motion usually causes radial velocity variations of several kilometers per second, as the spectra of these stars vary due to the Doppler effect, they are called spectroscopic binaries. Radial velocity can be used to estimate the ratio of the masses of the stars and it has been suggested that planets with high eccentricities calculated by this method may in fact be two-planet systems of circular or near-circular resonant orbit. When the star moves towards us, its spectrum is blueshifted, by regularly looking at the spectrum of a star—and so, measuring its velocity—it can be determined, if it moves periodically due to the influence of a companion. From the instrumental perspective, velocities are measured relative to the telescopes motion, in the case of spectroscopic measurements corrections of the order of ±20 cm/s with respect to aberration. Proper motion Peculiar velocity Relative velocity The Radial Velocity Equation in the Search for Exoplanets
9.
Cosmic distance ladder
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The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. A real direct distance measurement of an object is possible only for those objects that are close enough to Earth. The techniques for determining distances to more distant objects are all based on various measured correlations between methods that work at distances and methods that work at larger distances. Several methods rely on a candle, which is an astronomical object that has a known luminosity. The ladder analogy arises because no single technique can measure distances at all ranges encountered in astronomy, instead, one method can be used to measure nearby distances, a second can be used to measure nearby to intermediate distances, and so on. Each rung of the ladder provides information that can be used to determine the distances at the next higher rung, at the base of the ladder are fundamental distance measurements, in which distances are determined directly, with no physical assumptions about the nature of the object in question. The precise measurement of stellar positions is part of the discipline of astrometry, direct distance measurements are based upon the astronomical unit, which is the distance between the Earth and the Sun. Historically, observations of transits of Venus were crucial in determining the AU, in the first half of the 20th century, observations of asteroids were also important. Keplers laws provide precise ratios of the sizes of the orbits of objects orbiting the Sun, radar is used to measure the distance between the orbits of the Earth and of a second body. From that measurement and the ratio of the two sizes, the size of Earths orbit is calculated. The Earths orbit is known with a precision of a few meters, the most important fundamental distance measurements come from trigonometric parallax. As the Earth orbits the Sun, the position of stars will appear to shift slightly against the more distant background. These shifts are angles in a triangle, with 2 AU making the base leg of the triangle. The amount of shift is small, measuring 1 arcsecond for an object at the 1 parsec distance of the nearest stars. Astronomers usually express distances in units of parsecs, light-years are used in popular media, because parallax becomes smaller for a greater stellar distance, useful distances can be measured only for stars whose parallax is larger than a few times the precision of the measurement. Parallax measurements typically have an accuracy measured in milliarcseconds, the Hubble telescope WFC3 now has the potential to provide a precision of 20 to 40 microarcseconds, enabling reliable distance measurements up to 5,000 parsecs for small numbers of stars. By the early 2020s, the GAIA space mission will provide similarly accurate distances to all bright stars. Stars have a velocity relative to the Sun that causes proper motion, for a group of stars with the same spectral class and a similar magnitude range, a mean parallax can be derived from statistical analysis of the proper motions relative to their radial velocities
10.
Parsec
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The parsec is a unit of length used to measure large distances to objects outside the Solar System. One parsec is the distance at which one astronomical unit subtends an angle of one arcsecond, a parsec is equal to about 3.26 light-years in length. The nearest star, Proxima Centauri, is about 1.3 parsecs from the Sun, most of the stars visible to the unaided eye in the nighttime sky are within 500 parsecs of the Sun. The parsec unit was likely first suggested in 1913 by the British astronomer Herbert Hall Turner, named from an abbreviation of the parallax of one arcsecond, it was defined so as to make calculations of astronomical distances quick and easy for astronomers from only their raw observational data. Partly for this reason, it is still the unit preferred in astronomy and astrophysics, though the light-year remains prominent in science texts. This corresponds to the definition of the parsec found in many contemporary astronomical references. Derivation, create a triangle with one leg being from the Earth to the Sun. As that point in space away, the angle between the Sun and Earth decreases. A parsec is the length of that leg when the angle between the Sun and Earth is one arc-second. One of the oldest methods used by astronomers to calculate the distance to a star is to record the difference in angle between two measurements of the position of the star in the sky. The first measurement is taken from the Earth on one side of the Sun, and the second is approximately half a year later. The distance between the two positions of the Earth when the two measurements were taken is twice the distance between the Earth and the Sun. The difference in angle between the two measurements is twice the angle, which is formed by lines from the Sun. Then the distance to the star could be calculated using trigonometry. 5-parsec distance of 61 Cygni, the parallax of a star is defined as half of the angular distance that a star appears to move relative to the celestial sphere as Earth orbits the Sun. Equivalently, it is the angle, from that stars perspective. The star, the Sun and the Earth form the corners of a right triangle in space, the right angle is the corner at the Sun. Therefore, given a measurement of the angle, along with the rules of trigonometry. A parsec is defined as the length of the adjacent to the vertex occupied by a star whose parallax angle is one arcsecond
11.
Apparent magnitude
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The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value, the Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere, furthermore, the magnitude scale is logarithmic, a difference of one in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry, apparent magnitudes are used to quantify the brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or often simply as V, the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the sky were said to be of first magnitude, whereas the faintest were of sixth magnitude. Each grade of magnitude was considered twice the brightness of the following grade and this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to have originated with Hipparchus. This implies that a star of magnitude m is 2.512 times as bright as a star of magnitude m +1 and this figure, the fifth root of 100, became known as Pogsons Ratio. The zero point of Pogsons scale was defined by assigning Polaris a magnitude of exactly 2. However, with the advent of infrared astronomy it was revealed that Vegas radiation includes an Infrared excess presumably due to a disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures, however, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the scale was extrapolated to all wavelengths on the basis of the black body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, with the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30, astronomers have developed other photometric zeropoint systems as alternatives to the Vega system. The AB magnitude zeropoint is defined such that an objects AB, the dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor 5√100 ≈2.512. Inverting the above formula, a magnitude difference m1 − m2 = Δm implies a brightness factor of F2 F1 =100 Δ m 5 =100.4 Δ m ≈2.512 Δ m
12.
Galaxy morphological classification
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Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. The Hubble sequence is a classification scheme for galaxies invented by Edwin Hubble in 1926. It is often known colloquially as the “Hubble tuning-fork” because of the shape in which it is traditionally represented, Hubble’s scheme divides galaxies into three broad classes based on their visual appearance, Elliptical galaxies have smooth, featureless light distributions and appear as ellipses in images. They are denoted by the letter E, followed by an integer n representing their degree of ellipticity on the sky. Spiral galaxies consist of a disk, with stars forming a spiral structure, and a central concentration of stars known as the bulge. They are given the symbol S, roughly half of all spirals are also observed to have a bar-like structure, extending from the central bulge. These barred spirals are given the symbol SB and these broad classes can be extended to enable finer distinctions of appearance and to encompass other types of galaxies, such as irregular galaxies, which have no obvious regular structure. The Hubble sequence is represented in the form of a two-pronged fork, with the ellipticals on the left. Lenticular galaxies are placed between the ellipticals and the spirals, at the point where the two meet the “handle”. To this day, the Hubble sequence is the most commonly used system for classifying galaxies, the de Vaucouleurs system for classifying galaxies is a widely used extension to the Hubble sequence, first described by Gérard de Vaucouleurs in 1959. In particular, he argued that rings and lenses are important structural components of spiral galaxies, the de Vaucouleurs system retains Hubble’s basic division of galaxies into ellipticals, lenticulars, spirals and irregulars. For example, a barred spiral galaxy with loosely wound arms. Visually, the de Vaucouleurs system can be represented as a version of Hubble’s tuning fork, with stage on the x-axis, family on the y-axis. De Vaucouleurs also assigned numerical values to each class of galaxy in his scheme, values of the numerical Hubble stage T run from −6 to +10, with negative numbers corresponding to early-type galaxies and positive numbers to late types. Elliptical galaxies are divided into three stages, compact ellipticals, normal ellipticals and late types, lenticulars are similarly subdivided into early, intermediate and late types. Irregular galaxies can be of type magellanic irregulars or compact, the use of numerical stages allows for more quantitative studies of galaxy morphology. Created by American astronomer William Wilson Morgan, together with Philip Keenan, Morgan developed the MK system for the classification of stars through their spectra. The Yerkes scheme uses the spectra of stars in the galaxy, the shape, real and apparent, thus, for example, the Andromeda Galaxy is classified as kS5. H
13.
Angular diameter
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The angular diameter or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view. In the vision sciences it is called the angle and in optics it is the angular aperture. The angular diameter can alternatively be thought of as the angle through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side, Angular radius equals half the angular diameter. When D ≫ d, we have δ ≈ d / D, for practical use, the distinction is only significant for spherical objects that are relatively close, since the small-angle approximation holds for x ≪1, arcsin x ≈ arctan x ≈ x. Estimates of angular diameter may be obtained by holding the hand at right angles to an extended arm. In astronomy the sizes of objects in the sky are given in terms of their angular diameter as seen from Earth. Since these angular diameters are typically small, it is common to present them in arcseconds, an arcsecond is 1/3600th of one degree, and a radian is 180/ π degrees, so one radian equals 3600*180/ π arcseconds, which is about 206265 arcseconds. Therefore, the diameter of an object with physical diameter d at a distance D, expressed in arcseconds, is given by. These objects have a diameter of one arcsecond, an object of diameter 725. The angular diameter of the Sun, from a distance of one light-year, is 0. 03″, the angular diameter 0. 03″ of the Sun given above is approximately the same as that of a person at a distance of the diameter of the Earth. Thus the angular diameter of the Sun is about 250,000 times that of Sirius, the angular diameter of the Sun is also about 250,000 times that of Alpha Centauri A. The angular diameter of the Sun is about the same as that of the Moon, even though Pluto is physically larger than Ceres, when viewed from Earth Ceres has a much larger apparent size. While angular sizes measured in degrees are useful for larger patches of sky, we need much finer units when talking about the size of galaxies. The Moons motion across the sky can be measured in size, approximately 15 degrees every hour. A one-mile-long line painted on the face of the Moon would appear to us to be about one arc-second in length, in astronomy, it is typically difficult to directly measure the distance to an object. But the object may have a physical size and a measurable angular diameter. In that case, the angular diameter formula can be inverted to yield the Angular diameter distance to distant objects as d ≡2 D tan . In non-Euclidean space, such as our universe, the angular diameter distance is only one of several definitions of distance
14.
New General Catalogue
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The NGC contains 7,840 objects, known as the NGC objects. It is one of the largest comprehensive catalogues, as it includes all types of space objects and is not confined to, for example. Dreyer also published two supplements to the NGC in 1895 and 1908, known as the Index Catalogues, describing a further 5,386 astronomical objects. Objects in the sky of the southern hemisphere are catalogued somewhat less thoroughly, the Revised New General Catalogue and Index Catalogue was compiled in 2009 by Wolfgang Steinicke. The original New General Catalogue was compiled during the 1880s by John Louis Emil Dreyer using observations from William Herschel and his son John, Dreyer had already published a supplement to Herschels General Catalogue of Nebulae and Clusters, containing about 1,000 new objects. In 1886, he suggested building a second supplement to the General Catalogue and this led to the publication of the New General Catalogue in the Memoirs of the Royal Astronomical Society in 1888. Assembling the NGC was a challenge, as Dreyer had to deal with many contradicting and unclear reports, while he did check some himself, the sheer number of objects meant Dreyer had to accept them as published by others for the purpose of his compilation. Dreyer was a careful transcriber and made few errors himself, and he was very thorough in his referencing, which allowed future astronomers to review the original references and publish corrections to the original NGC. The first major update to the NGC is the Index Catalogue of Nebulae and Clusters of Stars and it serves as a supplement to the NGC, and contains an additional 5,386 objects, collectively known as the IC objects. It summarizes the discoveries of galaxies, clusters and nebulae between 1888 and 1907, most of them made possible by photography, a list of corrections to the IC was published in 1912. The Revised New Catalogue of Nonstellar Astronomical Objects was compiled by Jack W. Sulentic and William G. Tifft in the early 1970s, and was published in 1973, as an update to the NGC. However, because the update had to be completed in just three summers, it failed to incorporate several previously-published corrections to the NGC data, and even introduced new errors. NGC2000.0 is a 1988 compilation of the NGC and IC made by Roger W. Sinnott and it incorporates several corrections and errata made by astronomers over the years. However, it too ignored the original publications and favoured modern corrections, the NGC/IC Project is a collaboration formed in 1993. It aims to identify all NGC and IC objects, and collect images, the Revised New General Catalogue and Index Catalogue is a compilation made by Wolfgang Steinicke in 2009. It is considered one of the most comprehensive and authoritative treatments of the NGC, messier object Catalogue of Nebulae and Clusters of Stars The Interactive NGC Catalog Online Adventures in Deep Space, Challenging Observing Projects for Amateur Astronomers
15.
Principal Galaxies Catalogue
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The Catalogue of Principal Galaxies is an astronomical catalog published in 1989 that lists B1950 and J2000 equatorial coordinates and cross-identifications for 73,197 galaxies. It is based on the Lyon-Meudon Extragalactic Database, which was started in 1983. 40,932 coordinates have standard deviations smaller than 10″, a total of 131,601 names from the 38 most common sources are listed. The Lyon-Meudon Extragalactic Database was eventually expanded into HyperLEDA, a database of a few million galaxies, Galaxies in the original PGC catalogue are numbered with their original PGC number in HyperLEDA. Numbers have also assigned for the other galaxies, although for those galaxies not in the original PGC catalogue. PGC6240 is a lenticular galaxy in the constellation Hydrus. It is located about 106 million parsecs away from Earth, PGC39058 is a dwarf galaxy which is located approximately 14 million light years away in the constellation of Draco. It is relatively nearby, however it is obscured by a star which is in front of the galaxy. Astronomical catalogue PGC info at ESOs archive of astronomical catalogues PGC readme at Centre de Données astronomiques de Strasbourg
16.
Galaxy
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A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek galaxias, literally milky, Galaxies range in size from dwarfs with just a few billion stars to giants with one hundred trillion stars, each orbiting its galaxys center of mass. Galaxies are categorized according to their morphology as elliptical, spiral. Many galaxies are thought to have holes at their active centers. The Milky Ways central black hole, known as Sagittarius A*, has a four million times greater than the Sun. Recent estimates of the number of galaxies in the observable universe range from 200 billion to 2 trillion or more, most of the galaxies are 1,000 to 100,000 parsecs in diameter and separated by distances on the order of millions of parsecs. The space between galaxies is filled with a gas having an average density of less than one atom per cubic meter. The majority of galaxies are organized into groups, clusters. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids. In Greek mythology, Zeus places his son born by a mortal woman, the infant Heracles, on Heras breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing a baby, she pushes the baby away, some of her milk spills and. In the astronomical literature, the capitalized word Galaxy is often used to refer to our galaxy, the Milky Way, to distinguish it from the other galaxies in our universe. The English term Milky Way can be traced back to a story by Chaucer c. 1380, See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt. However, the word Universe was later understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies. Tens of thousands of galaxies have been catalogued, but only a few have well-established names, such as the Andromeda Galaxy, the Magellanic Clouds, the Whirlpool Galaxy, and the Sombrero Galaxy. Astronomers work with numbers from certain catalogues, such as the Messier catalogue, the NGC, the IC, the CGCG, all of the well-known galaxies appear in one or more of these catalogues but each time under a different number. For example, Messier 109 is a galaxy having the number 109 in the catalogue of Messier, but also codes NGC3992, UGC6937, CGCG 269-023, MCG +09-20-044. One of the arguments to do so is that these impressive objects deserve better than uninspired codes, for instance, Bodifee and Berger propose the informal, descriptive name Callimorphus Ursae Majoris for the well-formed barred galaxy Messier 109 in Ursa Major
17.
Intermediate spiral galaxy
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An intermediate spiral galaxy is a galaxy that is in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification scheme, by definition, a galaxy is a congregation of stars held together by gravity. The first intermediate spiral galaxy discovered is the Milky Way, by Galileo and he was the first person with a telescope powerful enough to make such a discovery. Before Galileo, it was thought that all objects in the sky were either the planets in the Solar System, moons, comets. Until the beginning on the century, astronomers did not know the size of the Universe. Nothing was resolved at the debate, neither side was able to provide evidence to prove their side correct over their opponent. In 1923, Edwin Hubble resolved the matter with a photograph that he took of the Andromeda Galaxy, what he found in his photograph was a very bright light source pulsing at a certain rate, a Cepheid variable, located outside the Milky Way. This can be used to determine the distance to it, Hubble proved that the Universe was full of galaxies, and disproved that the Milky Way was the extent of the Universe. There are many types of galaxies in the Universe, elliptical, barred spiral galaxies, they vary in shape and size, a galaxy starts out as a giant cloud of cold gas. The cloud of gas must be close to zero, if the gas cloud is too hot, the atoms will have too much kinetic energy. When a cloud reaches a mass of about 109−1011 times the mass of the Sun, for an intermediate spiral galaxy to form, the gas cloud must be rotating, and as the gas coalesces, the gas cloud will flatten out to form a disk shape. The mass remaining constant, to comply with the laws which govern the conservation of angular momentum. At the very center of the galaxy, the gas will condense so much under pressure that a supermassive black hole will form. All spiral galaxies have a hole at the center of their galaxy, called the galactic nucleus. The Central Bulge contains Population II stars, which are old stars, devoid of metals, for this reason the central bulge glows an orange/red color. The disk of the galaxy is full of star formation, and Population I stars, star formation takes place in the spiral arms of the galaxy. The rotation velocity of the galaxy is nearly uniform throughout the entire disk, the reason for this is due to an even bigger halo of postulated dark matter that extends beyond the size of the galaxy. This dark matter is to date made up of a substance which radiates no light
18.
Starburst galaxy
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As such, the starburst nature of a galaxy is a phase, and one that typically occupies a brief period of a galaxys evolution. The majority of starburst galaxies are in the midst of a merger or close encounter with another galaxy, Starburst galaxies include M82, NGC 4038/NGC4039, and IC10. Starburst galaxies are defined by three interrelated factors, The rate at which the galaxy is currently converting gas into stars. The available quantity of gas from which stars can be formed, a comparison of the timescale on which star formation will consume the available gas with the age or rotation period of the galaxy. Commonly used definitions include, Continued star-formation where the current SFR would exhaust the available gas reservoir in much less than the age of the Universe, Continued star-formation where the current SFR would exhaust the available gas reservoir in much less than the dynamical timescale of the galaxy. The current SFR, normalised by the past-averaged SFR, is greater than unity. This ratio is referred to as the birthrate parameter, Starburst galaxies feature a large amount of cool molecular gas in a small volume. Galaxies in the midst of a starburst also frequently show tidal tails, classifying types of starburst galaxies is difficult since starburst galaxies do not represent a specific type in and of themselves. Starbursts can occur in disk galaxies, and irregular galaxies often exhibit knots of starburst spread throughout the irregular galaxy, nevertheless, astronomers typically classify starburst galaxies based on their most distinct observational characteristics. Some of the include, Blue compact galaxies. These galaxies are often low mass, low metallicity, dust-free objects, because they are dust-free and contain a large number of hot, young stars, they are often blue in optical and ultraviolet colours. It was initially thought that BCGs were genuinely young galaxies in the process of forming their first generation of stars, however, old stellar populations have been found in most BCGs, and it is thought that efficient mixing may explain the apparent lack of dust and metals. Most BCGs show signs of recent mergers and/or close interactions, well-studied BCGs include IZw18, ESO338-IG04 and Haro11. Blue compact dwarf galaxies are small compact galaxies, green Pea galaxies are small compact galaxies resembling primordial starbursts. They were found by citizen scientists taking part in the Galaxy Zoo project and these galaxies are generally extremely dusty objects. The ultraviolet radiation produced by the obscured star-formation is absorbed by the dust and this explains the extreme red colours associated with ULIRGs. It is not known for sure that the UV radiation is produced purely by star-formation, Wolf-Rayet galaxies, galaxies where a large portion of the bright stars are Wolf-Rayet stars. The Wolf-Rayet phases is a relatively short-lived phase in the life of stars, typically 10% of the total life-time of these stars
19.
Star formation
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Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as stellar nurseries or star-forming regions, fuse to form stars. It is closely related to formation, another branch of astronomy. Star formation theory, as well as accounting for the formation of a star, must also account for the statistics of binary stars. In June 2015, astronomers reported evidence for Population III stars in the Cosmos Redshift 7 galaxy at z =6.60, a spiral galaxy like the Milky Way contains stars, stellar remnants, and a diffuse interstellar medium of gas and dust. The interstellar medium consists of 10−4 to 106 particles per cm3 and is composed of roughly 70% hydrogen by mass. This medium has been enriched by trace amounts of heavier elements that were ejected from stars as they passed beyond the end of their main sequence lifetime. Higher density regions of the interstellar medium form clouds, or diffuse nebulae, in the dense nebulae where stars are produced, much of the hydrogen is in the molecular form, so these nebulae are called molecular clouds. These giant molecular clouds have densities of 100 particles per cm3, diameters of 100 light-years, masses of up to 6 million solar masses. About half the mass of the galactic ISM is found in molecular clouds and in the Milky Way there are an estimated 6,000 molecular clouds. The nearest nebula to the Sun where massive stars are being formed is the Orion nebula,1,300 ly away, however, lower mass star formation is occurring about 400–450 light years distant in the ρ Ophiuchi cloud complex. A more compact site of formation is the opaque clouds of dense gas and dust known as Bok globules. These can form in association with collapsing molecular clouds or possibly independently, the Bok globules are typically up to a light year across and contain a few solar masses. They can be observed as dark clouds silhouetted against bright emission nebulae or background stars, over half the known Bok globules have been found to contain newly forming stars. An interstellar cloud of gas will remain in equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the theorem, which states that, to maintain equilibrium. If a cloud is massive enough that the gas pressure is insufficient to support it, the mass above which a cloud will undergo such collapse is called the Jeans mass. The Jeans mass depends on the temperature and density of the cloud and this coincides with the typical mass of an open cluster of stars, which is the end product of a collapsing cloud. In triggered star formation, one of several events occur to compress a molecular cloud
20.
Caroline Herschel
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She was the sister of astronomer William Herschel, with whom she worked throughout her career. She was the first woman to be awarded a Gold Medal of the Royal Astronomical Society and she was also named an honorary member of the Royal Irish Academy. The King of Prussia presented her with a Gold Medal for Science on the occasion of her 96th birthday, Caroline Lucretia Herschel was born in the town of Hanover on 16 March 1750. She was the child and fourth daughter of Isaac Herschel, a Jewish oboist. Isaac became a bandmaster in the Guards and was away with his regiment for substantial periods and he became ill after the Battle of Dettingen in 1743 and never recovered fully, suffering from a weak constitution, chronic pain, and asthma for the remainder of his life. The oldest of their daughters, Sophia, was the surviving girl besides Caroline. She married when Caroline was five, meaning that the girl was tasked with much of the household drudgery. Caroline and the children received a cursory education, learning to read and write. Her father attempted to educate her at home, but his efforts were successful with the boys. At the age of ten, Caroline was struck with typhus and she suffered vision loss in her left eye as a result of her illness. Her family assumed that she would never marry and her mother felt it was best for her to train to be a servant rather than becoming educated. Her father sometimes took advantage of her mothers absence to teach her directly or include her in her brothers lessons, Caroline was briefly allowed to learn dress-making. Though she learned to do needlework from a neighbor, her efforts were stymied by long hours of household chores. To prevent her becoming a governess and earning her independence that way. Following her fathers death, her brothers William and Alexander proposed that she join them in Bath, Caroline eventually left Hanover on 16 August 1772 after her brothers intervention with their recalcitrant mother. On the journey to England, she was first introduced to astronomy by way of the constellations and opticians shops and she took on the responsibilities of running Williams household in Bath, and began learning to sing. William had established himself as an organist and music teacher at 19 New King Street, Bath and he was also the choirmaster of the Octagon Chapel. William was busy with his career and became fairly busy organising public concerts
21.
Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model
22.
John Herschel
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Sir John Frederick William Herschel, 1st Baronet KH FRS was an English polymath, mathematician, astronomer, chemist, inventor, and experimental photographer, who also did valuable botanical work. He was the son of Mary Baldwin and astronomer William Herschel, nephew of astronomer Caroline Herschel, Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus, Herschel was born in Slough, Buckinghamshire, the son of Mary Baldwin and William Herschel. He studied shortly at Eton College and St Johns College, Cambridge and it was during his time as an undergraduate that he became friends with Charles Babbage and George Peacock. He left Cambridge in 1816 and started working with his father and he took up astronomy in 1816, building a reflecting telescope with a mirror 18 inches in diameter and with a 20-foot focal length. Between 1821 and 1823 he re-examined, with James South, the stars catalogued by his father. He was one of the founders of the Royal Astronomical Society in 1820, Herschel was made a Knight of the Royal Guelphic Order in 1831. He served as President of the Royal Astronomical Society three times, 1827–29, 1839–41 and 1847–49, a further complementary volume was published posthumously, as the General Catalogue of 10,300 Multiple and Double Stars. His views were published in an article entitled Light in 1828, the voyage to South Africa was made in order to catalogue the stars, nebulae, and other objects of the southern skies. This was to be a completion as well as extension of the survey of the northern heavens undertaken initially by his father William Herschel. He arrived in Cape Town on 15 January 1834 and set up a private 21 ft telescope at Feldhausen at Claremont, amongst his other observations during this time was that of the return of Comet Halley. Herschel collaborated with Thomas Maclear, the Astronomer Royal at the Cape of Good Hope, during this time, he also witnessed the Great Eruption of Eta Carinae. While in southern Africa, he engaged in a variety of scientific pursuits free from a sense of strong obligations to a larger scientific community. It was, he recalled, probably the happiest time in his life. Herschel used a camera lucida to obtain accurate outlines of the specimens, some 112 of the 132 known flower studies were collected and published as Flora Herscheliana in 1996. As their home during their stay in the Cape, the Herschels had selected Feldhausen, here John set up his reflector to begin his survey of the southern skies. — we must not impugn the Scripture Chronology, but we must interpret it in accordance with whatever shall appear on fair enquiry to be the truth for there cannot be two truths. And really there is enough, for the lives of the Patriarchs may as reasonably be extended to 5000 or 50000 years apiece as the days of Creation to as many thousand millions of years
23.
Reflecting telescope
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A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the telescope which. Although reflecting telescopes produce other types of aberrations, it is a design that allows for very large diameter objectives. Almost all of the telescopes used in astronomy research are reflectors. Reflecting telescopes come in many variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is referred to as a catoptric telescope. The idea that curved mirrors behave like lenses dates back at least to Alhazens 11th century treatise on optics, the potential advantages of using parabolic mirrors, primarily reduction of spherical aberration with no chromatic aberration, led to many proposed designs for reflecting telescopes. The most notable being James Gregory, who published a design for a ‘reflecting’ telescope in 1663. It would be ten years, before the experimental scientist Robert Hooke was able to build this type of telescope, Isaac Newton has been generally credited with building the first reflecting telescope in 1668. It used a spherically ground metal primary mirror and a diagonal mirror in an optical configuration that has come to be known as the Newtonian telescope. A curved primary mirror is the reflector telescopes basic optical element that creates an image at the focal plane, the distance from the mirror to the focal plane is called the focal length. The primary mirror in most modern telescopes is composed of a glass cylinder whose front surface has been ground to a spherical or parabolic shape. A thin layer of aluminum is deposited onto the mirror. Some telescopes use primary mirrors which are made differently, molten glass is rotated to make its surface paraboloidal, and is kept rotating while it cools and solidifies. The resulting mirror shape approximates a desired paraboloid shape that requires grinding and polishing to reach the exact figure needed. Reflecting telescopes, just like any other system, do not produce perfect images. The use of mirrors avoids chromatic aberration but they produce other types of aberrations, to avoid this problem most reflecting telescopes use parabolic shaped mirrors, a shape that can focus all the light to a common focus. Field curvature - The best image plane is in general curved and it is sometimes corrected by a field flattening lens
24.
Cape of Good Hope
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The Cape of Good Hope is a rocky headland on the Atlantic coast of the Cape Peninsula, South Africa. In fact, the southernmost point of Africa is Cape Agulhas, when following the western side of the African coastline from the equator, however, the Cape of Good Hope marks the point where a ship begins to travel more eastward than southward. Thus, the first modern rounding of the cape in 1488 by Portuguese explorer Bartolomeu Dias was a milestone in the attempts by the Portuguese to establish trade relations with the Far East. Dias called the cape Cabo das Tormentas, which was the name of the Cape of Good Hope. As one of the capes of the South Atlantic Ocean. It is a waypoint on the Cape Route and the route followed by clipper ships to the Far East and Australia. The term Cape of Good Hope is also used in three ways, It is a section of the Table Mountain National Park, within which the cape of the same name, as well as Cape Point. Prior to its incorporation into the park, this section constituted the Cape Point Nature Reserve. It was the name of the early Cape Colony established by the Dutch in 1652, just before the Union of South Africa was formed, the term referred to the entire region that in 1910 was to become the Cape of Good Hope Province. When Eudoxus was returning from his voyage to India the wind forced him south of the Gulf of Aden. Somewhere along the coast of East Africa, he found the remains of the ship, due to its appearance and the story told by the natives, Eudoxus concluded that the ship was from Gades and had sailed anti-clockwise around Africa, passing the Cape and entering the Indian Ocean. This inspired him to repeat the voyage and attempt a circumnavigation of the continent, organising the expedition on his own account he set sail from Gades and began to work down the African coast. The difficulties were too great, however, and he was obliged to return to Europe, after this failure he again set out to circumnavigate Africa. Although some, such as Pliny, claimed that Eudoxus did achieve his goal, in the 1450 Fra Mauro map, the Indian Ocean is depicted as connected to the Atlantic. It sailed for 40 days in a south-westerly direction without ever finding anything other than wind and water. According to these people themselves, the ship went some 2,000 miles ahead until - once favourable conditions came to an end - it turned round and sailed back to Cape Diab in 70 days. The ships called junks that navigate these seas carry four masts or more, some of which can be raised or lowered, and have 40 to 60 cabins for the merchants and only one tiller. They can navigate without a compass, because they have an astrologer, thus one can believe and confirm what is said by both these and those, and that they had therefore sailed 4,000 miles
25.
Allan Sandage
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Allan Rex Sandage was an American astronomer. He was Staff Member Emeritus with the Carnegie Observatories in Pasadena and he determined the first reasonably accurate values for the Hubble constant and the age of the universe. He also discovered the first quasar, Sandage was one of the most influential astronomers of the 20th century. He was born in Iowa City, Iowa, United States and he graduated from the University of Illinois in 1948. In 1953 he received a Ph. D. from the California Institute of Technology, during this time Sandage was a graduate student assistant to cosmologist Edwin Hubble. He continued Hubbles research program after Hubble died in 1953, Hubble had posited the earlier value, he had considered only the weaker Population II Cepheid variables as standard candles. This resulted in another 1.5 factor increase in the age of the universe. Sandage began working at the Palomar Observatory, in 1958 he published the first good estimate for the Hubble constant, revising Hubbles value of 250 down to 75 km/s/Mpc, which is close to todays accepted value. Later he became the advocate of an even lower value, around 50. Sandage performed photometric studies of clusters, and calculated their age to be at least 25 billion years. This led him to speculate that the universe did not merely expand, the current cosmological estimates of the age of the universe, in contrast, are typically of the order of 14 billion years. He later defended the paper in 1990 and this paper influenced observational cosmology for at least three decades as it carefully specified the types of observational tests that could be performed with a large telescope. He also published two atlases of galaxies, in 1961 and 1981, based on the Hubble classification scheme, in 1962 Sandage studied the possibility of directly measuring the temporal variation of the redshift of extra-galactic sources. This analysis became known as the Sandage–Loeb test, Sandage discovered jets erupting from the core of the so-called Cigar Galaxy. These must have been caused by explosions in the core. Sandage was a researcher, during his career he published more than 500 papers. Until his death he continued to be a researcher at the Carnegie Observatories. In 1959, Sandage married Mary Connelley, also an astronomer, in 1983 Sandage announced he had become a Christian and began to write essays on the subject of religion and science
26.
Sydney
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Sydney /ˈsɪdni/ is the state capital of New South Wales and the most populous city in Australia and Oceania. Located on Australias east coast, the metropolis surrounds the worlds largest natural harbour, residents of Sydney are known as Sydneysiders. The Sydney area has been inhabited by indigenous Australians for at least 30,000 years, the first British settlers, led by Captain Arthur Phillip, arrived in 1788 to found Sydney as a penal colony, the first European settlement in Australia. Since convict transportation ended in the century, the city has transformed from a colonial outpost into a major global cultural. As at June 2016 Sydneys estimated population was 5,005,358, in the 2011 census,34 percent of the population reported having been born overseas, representing many different nationalities and making Sydney one of the most multicultural cities in the world. There are more than 250 different languages spoken in Sydney and about one-third of residents speak a language other than English at home and it is classified as an Alpha+ World City by the Globalization and World Cities Research Network, indicating its influence in the region and throughout the world. Ranked eleventh in the world for economic opportunity, Sydney has a market economy with strengths in finance, manufacturing. Its gross regional product was $337 billion in 2013, the largest in Australia, there is a significant concentration of foreign banks and multinational corporations in Sydney and the city is promoted as one of Asia Pacifics leading financial hubs. Its natural features include Sydney Harbour, the Royal National Park, man-made attractions such as the Sydney Opera House, Sydney Tower and the Sydney Harbour Bridge are also well known to international visitors. The first people to inhabit the now known as Sydney were indigenous Australians having migrated from northern Australia. Radiocarbon dating suggests human activity first started to occur in the Sydney area from around 30,735 years ago, the earliest British settlers called them Eora people. Eora is the term the indigenous used to explain their origins upon first contact with the British. Its literal meaning is from this place, prior to the arrival of the British there were 4,000 to 8,000 native people in Sydney from as many as 29 different clans. Sydney Cove from Port Jackson to Petersham was inhabited by the Cadigal clan, the principal language groups were Darug, Guringai, and Dharawal. The earliest Europeans to visit the area noted that the people were conducting activities such as camping and fishing, using trees for bark and food, collecting shells. Development has destroyed much of the citys history including that of the first inhabitants, there continues to be examples of rock art and engravings located in the protected Ku-ring-gai Chase National Park. The first meeting between the people and the British occurred on 29 April 1770 when Lieutenant James Cook landed at Botany Bay on the Kurnell Peninsula. He noted in his journal that they were confused and somewhat hostile towards the foreign visitors, Cook was on a mission of exploration and was not commissioned to start a settlement
27.
Hubble Space Telescope
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The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Although not the first space telescope, Hubble is one of the largest and most versatile, with a 2. 4-meter mirror, Hubbles four main instruments observe in the near ultraviolet, visible, and near infrared spectra. Hubbles orbit outside the distortion of Earths atmosphere allows it to take extremely high-resolution images, Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as determining the rate of expansion of the universe. The HST was built by the United States space agency NASA, the Space Telescope Science Institute selects Hubbles targets and processes the resulting data, while the Goddard Space Flight Center controls the spacecraft. Space telescopes were proposed as early as 1923, Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster. When finally launched in 1990, Hubbles main mirror was found to have been ground incorrectly, the optics were corrected to their intended quality by a servicing mission in 1993. Hubble is the telescope designed to be serviced in space by astronauts. After launch by Space Shuttle Discovery in 1990, five subsequent Space Shuttle missions repaired, upgraded, the fifth mission was canceled on safety grounds following the Columbia disaster. However, after spirited public discussion, NASA administrator Mike Griffin approved the fifth servicing mission, the telescope is operating as of 2017, and could last until 2030–2040. Its scientific successor, the James Webb Space Telescope, is scheduled for launch in 2018, the history of the Hubble Space Telescope can be traced back as far as 1946, to the astronomer Lyman Spitzers paper Astronomical advantages of an extraterrestrial observatory. In it, he discussed the two advantages that a space-based observatory would have over ground-based telescopes. First, the resolution would be limited only by diffraction, rather than by the turbulence in the atmosphere. Second, a telescope could observe infrared and ultraviolet light. Spitzer devoted much of his career to pushing for the development of a space telescope, space-based astronomy had begun on a very small scale following World War II, as scientists made use of developments that had taken place in rocket technology. An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel space program, oAO-1s battery failed after three days, terminating the mission. It was followed by OAO-2, which carried out observations of stars and galaxies from its launch in 1968 until 1972. The continuing success of the OAO program encouraged increasingly strong consensus within the community that the LST should be a major goal
28.
Binoculars
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Binoculars or field glasses are two telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes when viewing distant objects. Most are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal mounted military models. Almost from the invention of the telescope in the 17th century the advantages of mounting two of them side by side for binocular vision seems to have been explored, most early binoculars used Galilean optics, that is, they used a convex objective and a concave eyepiece lens. The Galilean design has the advantage of presenting an image but has a narrow field of view and is not capable of very high magnification. This type of construction is used in very cheap models. They also have large exit pupils making centering less critical and the field of view works well in those applications. These are typically mounted on a frame or custom-fit onto eyeglasses. An improved image and higher magnification is achieved in binoculars employing Keplerian optics, since the Keplerian configuration produces an inverted image, different methods were used to turn the image right way up. In aprismatic binoculars with Keplerian optics each tube has one or two additional lenses between the objective and the ocular and these lenses are used to erect the image. The binoculars with erecting lenses have a disadvantage, their length is too long. Such binoculars were popular in the 1800s, but became obsolete shortly after the Karl Zeiss company introduced improved prism binoculars in the 1890s, Optical prisms added to the design are another way to turn the image right way up, usually in a Porro prism or roof-prisms design. Porro prism binoculars are named after Italian optician Ignazio Porro who patented this image erecting system in 1854, Binoculars of this type use a Porro prism in a double prism Z-shaped configuration to erect the image. This feature results in binoculars that are wide, with lenses that are well separated. Thus, the size of binoculars is reduced, Binoculars using roof prisms may have appeared as early as the 1870s in a design by Achille Victor Emile Daubresse. Most roof prism binoculars use either the Abbe-Koenig prism or the Schmidt-Pechan prism designs to erect the image and they have objective lenses that are approximately in line with the eyepieces. Roof-prisms designs create an instrument that is narrower and more compact than Porro prisms, there is also a difference in image brightness. Roof-prisms designs also require tighter tolerances for alignment of their optical elements and this adds to their expense since the design requires them to use fixed elements that need to be set at a high degree of collimation at the factory. Porro prisms binoculars occasionally need their prism sets to be re-aligned to bring them into collimation, the fixed alignment in roof-prism designs means the binoculars normally will not need re-collimation
29.
Beta Ceti
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Beta Ceti, also named Diphda, is the brightest star in the constellation of Cetus. Although designated beta, it is brighter than the alpha star in the constellation. This orange giant is easy to identify due to its location in a dark section of the celestial sphere. Based on parallax measurements, it lies at a distance of 96.3 light-years from the Sun. Diphda has an apparent visual magnitude of 2.02, making it the brightest star in Cetus. The stellar classification of this star is K0 III, although some sources list a classification of G9.5 III indicating that it lies along the line separating G-type from K-type stars. The luminosity class of III means that it is a giant star that has consumed the hydrogen at its core, after passing through the red giant stage, it underwent the helium flash event and is generating energy through the thermonuclear fusion of helium at its core. Beta Ceti will remain in this mode for over 100 million years, the effective temperature of the stars outer envelope is about 4,797 K, giving it the characteristic orange hue of a K-type star.8 times the Suns mass. This star displays flaring activity that results in random outbursts that increase the luminosity of the star over intervals lasting several days and this is a much longer duration than for comparable solar flare activity on the Sun, which typically last for periods measured in hours. In 2005, a high rate of X-ray emission was detected with the XMM-Newton space observatory. It is emitting about 2,000 times the X-ray luminosity of the Sun, β Ceti is the stars Bayer designation. It bore the traditional names Diphda and Deneb Kaitos, Diphda is Arabic for frog, from the phrase ضفدع الثاني aḍ-ḍifdaʿ aṯ-ṯānī the second frog, Deneb Kaitos is from ألذنب ألقيتوس ألجنوب Al Dhanab al Ḳaiṭos al Janūbīyy southern tail of Cetus. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalogue, USS Diphda was a U. S. Navy ship. Lists of stars in the constellation Cetus Beta Ceti, Giant Stars Corona Brightens with Age
30.
Andromeda Galaxy
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The Andromeda Galaxy, also known as Messier 31, M31, or NGC224, is a spiral galaxy approximately 780 kiloparsecs from Earth. It is the nearest major galaxy to the Milky Way and was referred to as the Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. Andromeda is approximately 220,000 light years across, and it is the largest galaxy of the Local Group, which contains the Milky Way, the Triangulum Galaxy. The mass of the Andromeda Galaxy is estimated to be 1. 5×1012 solar masses, the Milky Way and Andromeda galaxies are expected to collide in 4.5 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disc galaxy. Around the year 964, the Persian astronomer Abd al-Rahman al-Sufi described the Andromeda Galaxy, star charts of that period labeled it as the Little Cloud. In 1612, the German astronomer Simon Marius gave a description of the Andromeda Galaxy based on telescopic observations. In 1764, Charles Messier catalogued Andromeda as object M31 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye, in 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda. In 1850, William Parsons, 3rd Earl of Rosse, saw, in 1864, William Huggins noted that the spectrum of Andromeda differs from a gaseous nebula. The spectra of Andromeda displays a continuum of frequencies, superimposed with dark lines that help identify the chemical composition of an object. Andromedas spectrum is similar to the spectra of individual stars. In 1885, a supernova was seen in Andromeda, the first, at the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly, Nova 1885. In 1887, Isaac Roberts took the first photographs of Andromeda, Roberts actually mistook Andromeda and similar spiral nebulae as solar systems being formed. In 1912, Vesto Slipher used spectroscopy to measure the velocity of Andromeda with respect to our solar system—the largest velocity yet measured. In 1917, Heber Curtis observed a nova within Andromeda, searching the photographic record,11 more novae were discovered. Curtis noticed that these novae were, on average,10 magnitudes fainter than those that occurred elsewhere in the sky, as a result, he was able to come up with a distance estimate of 500,000 light-years. He became a proponent of the island universes hypothesis, which held that spiral nebulae were actually independent galaxies. In 1920, the Great Debate between Harlow Shapley and Curtis took place, concerning the nature of the Milky Way, spiral nebulae, in 1922 Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars
31.
Disc (galaxy)
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A disc is a component of disk galaxies, such as spiral galaxies, or lenticular galaxies. The galactic disc is the plane in which the spirals, bars, Galactic discs tend to have more gas and dust and younger stars than galactic bulges or galactic haloes. The galactic disc is composed of gas, dust and stars. The gas and dust component of the disc is called the gaseous disc. The star component of the disc is called the stellar disc. It has been noted that the velocity of stars in the disc of most disc galaxies is inconsistent with the amount of luminous matter calculated for the galaxy. A possible explanation for this problem is the dark matter. Galactic spheroid Galactic corona Tully–Fisher relation MOND Van Der Kruit, P. C, annual Review of Astronomy and Astrophysics
32.
Atacama Large Millimeter Array
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The Atacama Large Millimeter Array is an astronomical interferometer of radio telescopes in the Atacama desert of northern Chile. ALMA is a partnership among Europe, the United States, Canada, Japan, South Korea, Taiwan. Costing about US$1.4 billion, it is the most expensive ground-based telescope in operation, ALMA began scientific observations in the second half of 2011 and the first images were released to the press on 3 October 2011. The array has been operational since March 2013. The initial ALMA array is composed of 66 high-precision antennas, the high sensitivity is mainly achieved through the large numbers of antenna dishes that will make up the array. The telescopes were provided by the European, North American and East Asian partners of ALMA, the American and European partners each provided twenty-five 12-meter diameter antennas, that compose the main array. The participating East Asian countries are contributing 16 antennas in the form of the Atacama Compact Array, by using smaller antennas than the main ALMA array, larger fields of view can be imaged at a given frequency using ACA. Placing the antennas closer together enables the imaging of sources of larger angular extent, the ACA works together with the main array in order to enhance the latters wide-field imaging capability. ALMA has its roots in three astronomical projects — the Millimeter Array of the United States, the Large Southern Array of Europe. The merged array combined the sensitivity of the LSA with the frequency coverage, ESO and NRAO worked together in technical, science, and management groups to define and organize a joint project between the two observatories with participation by Canada and Spain. A groundbreaking ceremony was held on November 6,2003 and the ALMA logo was unveiled and this was mainly for political reasons. Although very different approaches have been chosen by the providers, each of the antenna designs appears to be able to meet ALMAs stringent requirements, ALMA is the largest and most expensive ground-based astronomical project, costing between US$1.4 and 1.5 billion. S. Japanese, and Canadian companies and universities, three prototype antennas have undergone evaluation at the Very Large Array since 2002. The first antenna was delivered in 2008, the last in 2011, the solution chosen is to use two custom 28-wheel self-loading heavy haulers. The vehicles were made by Scheuerle Fahrzeugfabrik in Germany and are 10 m wide,20 m long and 6 m high and they are powered by twin turbocharged 500 kW Diesel engines. The transporters, which feature a drivers seat designed to accommodate an oxygen tank to aid breathing the thin high-altitude air, the first vehicle was completed and tested in July 2007. Both transporters were delivered to the ALMA Operations Support Facility in Chile on 15 February 2008, on 7 July 2008, an ALMA transporter moved an antenna for the first time, from inside the antenna assembly building to a pad outside the building for testing. During Autumn 2009, the first three antennas were transported one-by-one to the Array Operations Site, linking three antennas allows corrections of errors that can arise when only two antennas are used, thus paving the way for precise, high-resolution imaging
33.
NASA
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President Dwight D. Eisenhower established NASA in 1958 with a distinctly civilian orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29,1958, disestablishing NASAs predecessor, the new agency became operational on October 1,1958. Since that time, most US space exploration efforts have led by NASA, including the Apollo Moon landing missions, the Skylab space station. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle, the agency is also responsible for the Launch Services Program which provides oversight of launch operations and countdown management for unmanned NASA launches. NASA shares data with various national and international such as from the Greenhouse Gases Observing Satellite. Since 2011, NASA has been criticized for low cost efficiency, from 1946, the National Advisory Committee for Aeronautics had been experimenting with rocket planes such as the supersonic Bell X-1. In the early 1950s, there was challenge to launch a satellite for the International Geophysical Year. An effort for this was the American Project Vanguard, after the Soviet launch of the worlds first artificial satellite on October 4,1957, the attention of the United States turned toward its own fledgling space efforts. This led to an agreement that a new federal agency based on NACA was needed to conduct all non-military activity in space. The Advanced Research Projects Agency was created in February 1958 to develop technology for military application. On July 29,1958, Eisenhower signed the National Aeronautics and Space Act, a NASA seal was approved by President Eisenhower in 1959. Elements of the Army Ballistic Missile Agency and the United States Naval Research Laboratory were incorporated into NASA, earlier research efforts within the US Air Force and many of ARPAs early space programs were also transferred to NASA. In December 1958, NASA gained control of the Jet Propulsion Laboratory, NASA has conducted many manned and unmanned spaceflight programs throughout its history. Some missions include both manned and unmanned aspects, such as the Galileo probe, which was deployed by astronauts in Earth orbit before being sent unmanned to Jupiter, the experimental rocket-powered aircraft programs started by NACA were extended by NASA as support for manned spaceflight. This was followed by a space capsule program, and in turn by a two-man capsule program. This goal was met in 1969 by the Apollo program, however, reduction of the perceived threat and changing political priorities almost immediately caused the termination of most of these plans. NASA turned its attention to an Apollo-derived temporary space laboratory, to date, NASA has launched a total of 166 manned space missions on rockets, and thirteen X-15 rocket flights above the USAF definition of spaceflight altitude,260,000 feet. The X-15 was an NACA experimental rocket-powered hypersonic research aircraft, developed in conjunction with the US Air Force, the design featured a slender fuselage with fairings along the side containing fuel and early computerized control systems
34.
European Space Agency
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The European Space Agency is an intergovernmental organisation of 22 member states, dedicated to the exploration of space. Established in 1975 and headquartered in Paris, France, ESA has a staff of about 2,000. The main European launch vehicle Ariane 5 is operated through Arianespace with ESA sharing in the costs of launching, after World War II, many European scientists left Western Europe in order to work with the United States. The meeting was attended by representatives from eight countries, including Harrie Massey. The Western European nations decided to have two different agencies, one concerned with developing a system, ELDO, and the precursor of the European Space Agency. The latter was established on 20 March 1964 by an agreement signed on 14 June 1962, from 1968 to 1972, ESRO launched seven research satellites. ESA in its current form was founded with the ESA Convention in 1975, ESA has 10 founding member states, Belgium, Denmark, France, Germany, Italy, the Netherlands, Spain, Sweden, Switzerland and the United Kingdom. These signed the ESA Convention in 1975 and deposited the instruments of ratification by 1980, during this interval the agency functioned in a de facto fashion. ESA launched its first major scientific mission in 1975, Cos-B, ESA joined NASA in the IUE, the worlds first high-orbit telescope, which was launched in 1978 and operated very successfully for 18 years. A number of successful Earth-orbit projects followed, and in 1986 ESA began Giotto, its first deep-space mission, to study the comets Halley and Grigg–Skjellerup. Hipparcos, a mission, was launched in 1989 and in the 1990s SOHO, Ulysses. Recent scientific missions in co-operation with NASA include the Cassini–Huygens space probe, as the successor of ELDO, ESA has also constructed rockets for scientific and commercial payloads. Ariane 1, launched in 1979, brought mostly commercial payloads into orbit from 1984 onward, the successor launch vehicle of Ariane 5, the Ariane 6 is already in the definition stage and is envisioned to enter service in the 2020s. The beginning of the new millennium saw ESA become, along with agencies like NASA, JAXA, ISRO, CSA and Roscosmos, one of the major participants in scientific space research. Although ESA had relied on co-operation with NASA in previous decades, especially the 1990s, changed circumstances led to decisions to rely more on itself, a 2011 press issue thus stated, Russia is ESAs first partner in its efforts to ensure long-term access to space. ESA maintains its scientific and research projects mainly for astronomy-space missions such as Corot, launched on 27 December 2006 and this is the reason space exploration is an integral part of overall space activities. It has always been so, and it will be more important in the future. ESA describes its work in two overlapping ways, For the general public the various fields of work are described as Activities, Member states participate to varying degrees in the mandatory and optional space programmes
35.
Sculptor Group
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The Sculptor Group is a loose group of galaxies near the south galactic pole. The group is one of the closest groups of galaxies to the Local Group, the Sculptor Galaxy and a few other galaxies form a gravitationally-bound core in the center of this group. A few other galaxies at the periphery may be associated with the group, because most of the galaxies in this group are actually weakly gravitationally bound, the group may also be described as a filament. It is considered to be at a stage of evolution in which galaxies are still falling into the group along filamentary structures. The table below lists galaxies that have identified as associated with the Sculptor Galaxy by I. D. Karachentsev. The object names used in the table differ from the names used by Karachentsev. NGC, IC, UGC, and PGC numbers have been used when possible to allow for easier referencing, the irregular galaxy NGC55, the spiral galaxy NGC300, and their companion galaxies have been considered by many researchers to be part of this group
36.
Galaxy group
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The groups and clusters of galaxies can themselves be clustered, into superclusters of galaxies. The Milky Way galaxy is part of a group of galaxies called the Local Group, Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs and their mass is approximately 1013 solar masses. The spread of velocities for the galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger, Groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a range between those of the very large elliptical galaxies and clusters of galaxies. In the local universe, about half of the groups exhibit diffuse X-ray emissions from their intracluster media and those that emit X-rays appear to have early-type galaxies as members. The diffuse X-ray emissions come from zones within the inner 10-50% of the virial radius. There are several subtypes of groups, Compact groups are small groups in closely grouped in a small area. They typically have around 5 galaxies in close proximity relatively isolated from other galaxies, the first discovered, Stephans Quintet, was discovered in 1877. Though Stephans Quintet itself is a group of 4 and a foreground galaxy. Astronomer Paul Hickson created a catalogue of such groups in 1982, Compact groups of galaxies readily show the effect of dark matter, as the visible mass is greatly less than that needed to dynamically bind the galaxies into a bound group. Compact galaxy groups are also not dynamically stable over Hubble time, fossil galaxy groups, fossil groups, or fossil clusters are believed to be the end-result of galaxy merging within a normal galaxy group, leaving behind the X-ray halo of the progenitor group. Galaxies within a group interact and merge, the physical process behind this galaxy-galaxy merger is dynamical friction. The time-scales for dynamical friction on luminous galaxies suggest that groups are old. Fossil groups are thus an important laboratory for studying the formation and evolution of galaxies, fossil groups may still contain unmerged dwarf galaxies, but the more massive members of the group have condensed into the central galaxy. The closest fossil group to the Milky Way is NGC6482, proto-groups are groups that are in the process of formation. They are the form of protoclusters
37.
Milky Way
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The Milky Way is the galaxy that contains our Solar System. The descriptive milky is derived from the appearance from Earth of the galaxy – a band of light seen in the night sky formed from stars that cannot be distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610, until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies, the Milky Way is a barred spiral galaxy with a diameter between 100,000 light-years and 180,000 light-years. The Milky Way is estimated to contain 100–400 billion stars, there are probably at least 100 billion planets in the Milky Way. The Solar System is located within the disk, about 26,000 light-years from the Galactic Center, on the edge of one of the spiral-shaped concentrations of gas. The stars in the inner ≈10,000 light-years form a bulge, the very center is marked by an intense radio source, named Sagittarius A*, which is likely to be a supermassive black hole. Stars and gases at a range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been termed dark matter, the rotational period is about 240 million years at the position of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to frames of reference. The oldest stars in the Milky Way are nearly as old as the Universe itself, the Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which is a component of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster. The Milky Way can be seen as a band of white light some 30 degrees wide arcing across the sky. Dark regions within the band, such as the Great Rift, the area of the sky obscured by the Milky Way is called the Zone of Avoidance. The Milky Way has a low surface brightness. Its visibility can be reduced by background light such as light pollution or stray light from the Moon. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be seen and it should be visible when the limiting magnitude is approximately +5.1 or better and shows a great deal of detail at +6.1
38.
Sombrero Galaxy
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Sombrero Galaxy is an unbarred spiral galaxy in the constellation Virgo located 31 million light-years from Earth. The galaxy has a diameter of approximately 50,000 light-years and it has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero and its large bulge, its central supermassive black hole, and its dust lane all attract the attention of professional astronomers. The Sombrero Galaxy was discovered on May 11,1781 by Pierre Méchain, charles Messier made a hand-written note about this and five other objects to his personal list of objects now known as the Messier Catalogue, but it was not officially included until 1921. William Herschel independently discovered the object in 1784 and additionally noted the presence of a stratum in the galaxys disc. Later astronomers were able to connect Méchains and Herschels observations, in 1921, Camille Flammarion found Messiers personal list of the Messier objects including the hand-written notes about the Sombrero Galaxy. This was identified with object 4594 in the New General Catalogue, since this time, the Sombrero Galaxy has been known as M104. As noted above, this galaxys most striking feature is the dust lane that crosses in front of the bulge of the galaxy and this dust lane is actually a symmetrical ring that encloses the bulge of the galaxy. Most of the atomic hydrogen gas and the dust lie within this ring. The ring might also contain most of the Sombrero Galaxys cold molecular gas, although this is an based on observations with low resolution. Additional observations are needed to confirm that the Sombrero galaxys molecular gas is constrained to the ring, based on infrared spectroscopy, the dust ring is the primary site of star formation within this galaxy. The nucleus of the Sombrero galaxy is classified as a low ionization nuclear emission region and these are nuclear regions where ionized gas is present, but the ions are only weakly ionized. The source of energy for ionizing the gas in LINERs has been debated extensively, some LINER nuclei may be powered by hot, young stars found in star formation regions, whereas other LINER nuclei may be powered by active galactic nuclei. Infrared spectroscopy observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a black hole has been identified in the nucleus. In the 1990s, a group led by John Kormendy demonstrated that a supermassive black hole is present within the Sombrero Galaxy. This is among the most massive black holes measured in any nearby galaxies, at radio and X-ray wavelengths, the nucleus is a strong source of synchrotron emission. Synchrotron emission is produced when high velocity electrons oscillate as they pass through regions with strong magnetic fields and this emission is quite common for active galactic nuclei
39.
NGC 247
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NGC247 is an intermediate spiral galaxy about 11.1 Mly away in the constellation Cetus. This distance was confirmed in late February 2011, previous measurements showed that the galaxy was about 12.2 Mly away, but this was proved to be wrong. NGC247 is a member of the Sculptor Group, NGC247 is marred by an unusually large void on one side of its spiral disk. This void contains some older, redder stars but no younger, bluer stars, NGC247 is one of several galaxies that is gravitationally bound to the Sculptor Galaxy. These galaxies form a core in the center of the Sculptor Group. Most other galaxies associated with the Sculptor Group are only weakly bound to this core. NGC247 on WikiSky, DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
40.
Solar mass
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The solar mass is a standard unit of mass in astronomy, equal to approximately 1.99 ×1030 kilograms. It is used to indicate the masses of stars, as well as clusters, nebulae. It is equal to the mass of the Sun, about two kilograms, M☉ = ×1030 kg The above mass is about 332946 times the mass of Earth. Because Earth follows an orbit around the Sun, its solar mass can be computed from the equation for the orbital period of a small body orbiting a central mass. The value he obtained differs by only 1% from the modern value, the diurnal parallax of the Sun was accurately measured during the transits of Venus in 1761 and 1769, yielding a value of 9″. From the value of the parallax, one can determine the distance to the Sun from the geometry of Earth. The first person to estimate the mass of the Sun was Isaac Newton, in his work Principia, he estimated that the ratio of the mass of Earth to the Sun was about 1/28700. Later he determined that his value was based upon a faulty value for the solar parallax and he corrected his estimated ratio to 1/169282 in the third edition of the Principia. The current value for the parallax is smaller still, yielding an estimated mass ratio of 1/332946. As a unit of measurement, the solar mass came into use before the AU, the mass of the Sun has been decreasing since the time it formed. This occurs through two processes in nearly equal amounts, first, in the Suns core, hydrogen is converted into helium through nuclear fusion, in particular the p–p chain, and this reaction converts some mass into energy in the form of gamma ray photons. Most of this energy eventually radiates away from the Sun, second, high-energy protons and electrons in the atmosphere of the Sun are ejected directly into outer space as a solar wind. The original mass of the Sun at the time it reached the main sequence remains uncertain, the early Sun had much higher mass-loss rates than at present, and it may have lost anywhere from 1–7% of its natal mass over the course of its main-sequence lifetime. The Sun gains a small amount of mass through the impact of asteroids. However, as the Sun already contains 99. 86% of the Solar Systems total mass, M☉ G / c2 ≈1.48 km M☉ G / c3 ≈4.93 μs I. -J. A Bright Young Sun Consistent with Helioseismology and Warm Temperatures on Ancient Earth and Mars
41.
Cosmic dust
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Cosmic dust, or Extraterrestrial dust, is dust which exists in outer space, as well as all over planet Earth. Most cosmic dust particles are between a few molecules to 0.1 µm in size, a smaller fraction of all dust in space consists of larger refractory minerals that condensed as matter left the stars. It is called stardust and is included in a section below. The dust density falling to Earth is approximately 10−6/m3 with each grain having a mass between 10−16kg and 10−4 kg, cosmic dust can be further distinguished by its astronomical location, intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust. In the Solar System, interplanetary dust causes the zodiacal light, sources of Solar System dust include comet dust, asteroidal dust, dust from the Kuiper belt, and interstellar dust passing through the Solar System. The terminology has no application for describing materials found on the planet Earth except for dust that has demonstrably fallen to Earth. By one estimate, as much as 40,000 tons of cosmic dust reaches the Earths surface every year, in October 2011, scientists reported that cosmic dust contains complex organic matter that could be created naturally, and rapidly, by stars. In August 2014, scientists announced the collection of interstellar dust particles from the Stardust spacecraft since returning to Earth in 2006. In March 2017, scientists reported that extraterrestrial dust particles have been identified all over planet Earth. According to one of the researchers, “Once I knew what to look for, I found them everywhere. ”Cosmic dust was once solely an annoyance to astronomers, when infrared astronomy began, those dust particles were observed to be significant and vital components of astrophysical processes. Their analysis can reveal information about phenomena like the formation of the Solar System, for example, cosmic dust can drive the mass loss when a star is nearing the end of its life, play a part in the early stages of star formation, and form planets. In the Solar System, dust plays a role in the zodiacal light, Saturns B Ring spokes, the outer diffuse planetary rings at Jupiter, Saturn, Uranus and Neptune. These disparate research areas can be linked by the following theme, the astronomers accumulate observational ‘snapshots’ of dust at different stages of its life and, over time, form a more complete movie of the Universes complicated recycling steps. Parameters such as the initial motion, material properties, intervening plasma. Slightly changing any of these parameters can give significantly different dust dynamical behavior, therefore, one can learn about where that object came from, and what is the intervening medium. Cosmic dust can be detected by indirect methods utilizing the properties of cosmic dust. Cosmic dust can also be detected using a variety of collection methods. Estimates of the influx of extraterrestrial material entering the Earths atmosphere range between 5 and 300 tonnes
. Bibcode:2005AJ....129..178K. doi:10.1086/426368.
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