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Comet C/2002 V1 (NEAT) is a non-periodic comet that appeared in November 2002. [ 1 ] The comet peaked with an apparent magnitude of approximately –0.5, making it the 8th brightest comet seen since 1935. [ 4 ] It was seen by SOHO in February 2003. At perihelion the comet was only 0.099258 AU (14,848,800 km ; 9,226,600 mi ) from the Sun. (Slight controversy arose when the comet failed to break up when it approached the sun, as expected by some scientists if it were a small comet.) [ 5 ]
99942 Apophis ( pron.: / ə ˈ p ɒ f ɪ s / , previously known by its provisional designation 2004 MN 4 ) is a near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a probability of up to 2.7% that it would strike the Earth in 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. However, a possibility remained that during the 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole , a small region no more than about 800 m (half a mile) wide, [ 7 ] that would set up a future impact on April 13, 2036. This possibility kept the asteroid at Level 1 on the Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small.
Comet C/2010 X1 (Elenin) is a long-period comet discovered by Russian amateur astronomer Leonid Elenin on December 10, 2010, through remote control of the International Scientific Optical Network 's robotic observatory near Mayhill in the U.S. state of New Mexico . The discovery was made using the automated asteroids discovery program CoLiTec . At the time of discovery, the comet had an apparent magnitude of 19.5, [ 2 ] making it about 150,000 times fainter than can be seen with the naked eye . [ 5 ] The discoverer, Leonid Elenin, originally estimated that the comet nucleus was 3–4 km in diameter, [ 6 ] but more recent estimates place the pre-breakup size of the comet at 2 km. [ 7 ] Comet Elenin started disintegrating in August 2011, [ 8 ] and as of mid-October 2011 was not visible even using large ground-based telescopes. [ 9 ] [ edit ] Brightness
Arcturus ( pron.: / ɑr k ˈ tj ʊər ə s / ; α Boo, α Boötis, Alpha Boötis) is the brightest star in the constellation Boötes and the northern celestial hemisphere . With a visual magnitude of −0.04, it is the fourth brightest star in the night sky , after −1.46 magnitude Sirius , −0.86 magnitude Canopus , and −0.27 magnitude Alpha Centauri . It is a relatively close star at only 36.7 light-years from Earth, and, together with Vega and Sirius, one of the most luminous stars in the Sun 's neighborhood. A type K1.5 IIIpe orange giant star, with an absolute magnitude of -0.30.
In astronomy , the Pleiades ( pron.: / ˈ p l aɪ . ə d iː z / or / ˈ p l iː . ə d iː z / ), or Seven Sisters ( Messier object 45 or M45 ), is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus . It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky . The name Pleiades comes from Greek mythology ; the celestial entity has several meanings in different cultures and traditions . The cluster is dominated by hot blue and extremely luminous stars that have formed within the last 100 million years. Dust that forms a faint reflection nebulosity around the brightest stars was thought at first to be left over from the formation of the cluster (hence the alternate name Maia Nebula after the star Maia ), but is now known to be an unrelated dust cloud in the interstellar medium that the stars are currently passing through.
Zeta Reticuli ( Zeta Ret , ζ Reticuli , ζ Ret ) is the Bayer designation for a wide binary star system in the southern constellation of Reticulum . From the southern hemisphere the pair can be seen as a naked eye double star in very dark skies . Based upon parallax measurements, this system is located at a distance of about 39 light-years (12 parsecs ) from the Earth . Zeta 2 Reticuli is orbited by a circumstellar debris disk . Both stars are solar analogs that share similar characteristics with the Sun. They belong to the Zeta Herculis Moving Group of stars that share a common origin.
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus , the next brightest star . The name "Sirius" is derived from the Ancient Greek : Σείριος Seirios ("glowing" or "scorcher"). The star has the Bayer designation Alpha Canis Majoris (α CMa). What the naked eye perceives as a single star is actually a binary star system, consisting of a white main-sequence star of spectral type A1V, termed Sirius A , and a faint white dwarf companion of spectral type DA2, called Sirius B .
The Draco Dwarf is a spheroidal galaxy which was discovered by Albert George Wilson of Lowell Observatory in 1954 on photographic plates of the National Geographic Society's Palomar Observatory Sky Survey (POSS). [ 5 ] It is part of the local group and a satellite galaxy of the Milky Way galaxy . The Draco Dwarf is situated in the direction of the Draco Constellation at 34.6° [ 6 ] above the galactic plane . [ edit ] Characteristics
The Andromeda–Milky Way collision is a galaxy collision predicted to occur in about 4 billion years between the two largest galaxies in the Local Group —the Milky Way (which contains the Solar System and Earth ) and the Andromeda Galaxy . [ 1 ] [ 2 ] [ 3 ] [ edit ] Stellar collisions While the Andromeda Galaxy contains about 1 trillion (10 12 ) stars and the Milky Way contains about 300 billion (3 × 10 11 ), the chance of even two stars colliding is negligible because of the huge distances between the stars. For example, the nearest star to the Sun is Proxima Centauri , about 4.2 light-years (4.0 × 10 13 km; 2.5 × 10 13 mi) or 30 million (3 × 10 7 ) solar diameters away.
A satellite galaxy orbits a larger galaxy due to gravitational attraction . Although a galaxy is made of a large number of objects (such as stars , planets , and nebulae ) which are not connected to each other, it has a center of mass , which represents a weighted average (by mass) of the positions of each component object. This is similar to how an everyday object has a center of mass which is the weighted average of the positions of all its component atoms . In a pair of orbiting galaxies, if one is considerably larger than the other, then the larger is the "primary" and the smaller is the satellite .
The Universe is commonly defined as the totality of existence, [ 1 ] [ 2 ] [ 3 ] [ 4 ] including planets , stars , galaxies , the contents of intergalactic space , and all matter and energy . [ 5 ] [ 6 ] The broadest definition of universe is that it is simply everything, while a narrower definition is that the universe is limited to what can be observed. [ dubious ] Similar terms include the cosmos , the world and nature .