Taurus (constellation)

Taurus is one of the constellations of the zodiac and is located in the northern celestial hemisphere. Taurus is a large and prominent constellation in the Northern Hemisphere's winter sky. It is one of the oldest constellations, dating back to the Early Bronze Age at least, when it marked the location of the Sun during the spring equinox. Its importance to the agricultural calendar influenced various bull figures in the mythologies of Ancient Sumer, Akkad, Assyria, Babylon, Egypt, Greece, and Rome. Its traditional astrological symbol is 20px, which resembles a bull's head.
A number of features exist that are of interest to astronomers. Taurus hosts two of the nearest open clusters to Earth, the Pleiades and the Hyades, both of which are visible to the naked eye. At first magnitude, the red giant Aldebaran is the brightest star in the constellation. In the northeast part of Taurus is Messier 1, more commonly known as the Crab Nebula, a supernova remnant containing the Crab Pulsar. One of the closest regions of active star formation, the Taurus-Auriga complex, crosses into the northern part of the constellation. The variable star T Tauri is the prototype of a class of pre-main-sequence stars.

Characteristics

Taurus is a large and prominent constellation in the Northern Hemisphere's winter sky, between Aries to the west and Gemini to the east; to the north lies Perseus and Auriga, to the southeast Orion, to the south Eridanus, and to the southwest Cetus. In late November-early December, Taurus reaches opposition and is visible the entire night. By late March, it is setting at sunset and completely disappears behind the Sun's glare from May to July.
This constellation forms part of the zodiac and hence is intersected by the ecliptic. This circle across the celestial sphere forms the apparent path of the Sun as the Earth completes its annual orbit. As the orbital plane of the Moon and the planets lie near the ecliptic, they can usually be found in the constellation Taurus during some part of each year. The galactic plane of the Milky Way intersects the northeast corner of the constellation and the galactic anticenter is located near the border between Taurus and Auriga. Taurus is the only constellation crossed by all three of the galactic equator, celestial equator, and ecliptic. A ring-like galactic structure known as Gould's Belt passes through the constellation.
The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Tau". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of 26 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between and, while the declination coordinates are between 31.10° and −1.35°. Because a small part of the constellation lies to the south of the celestial equator, this can not be a completely circumpolar constellation at any latitude.

Features

Stars

Bayer gave the most prominent stars Bayer designations Alpha through Omega, and the Latin letters A through u. Later designated three stars as Delta and two stars as Theta, Kappa, Sigma, Omega, and the Latin letter A. The star g Tauri was dropped after it was found to be a duplicate of Kappa Ceti
There are four stars above magnitude 3 in Taurus. The brightest member of this constellation is Aldebaran, an orange-hued, spectral class K5 III giant star. Its name derives from wikt:الدبران , Arabic for "the follower", probably from the fact that it follows the Pleiades during the nightly motion of the celestial sphere across the sky. Forming the profile of a Bull's face is a V or K-shaped asterism of stars. This outline is created by prominent members of the Hyades, the nearest distinct open star cluster after the Ursa Major Moving Group. In this profile, Aldebaran forms the bull's bloodshot eye, which has been described as "glaring menacingly at the hunter Orion", a constellation that lies just to the southeast. Aldebaran has around 116% the mass of the Sun. It also hosts a candidate exoplanet.
The Hyades span about 5° of the sky, so that they can only be viewed in their entirety with binoculars or the unaided eye. It includes a naked eye double star, Theta Tauri, with a separation of 5.6 arcminutes.
File:Triple Stellar Treat.jpg|thumb|HP Tauri, a T Tauri variable star and triple system
In the northwestern quadrant of the Taurus constellation lie the Pleiades, one of the best known open clusters, easily visible to the naked eye. The seven most prominent stars in this cluster are at least visual magnitude six, and so the cluster is also named the "Seven Sisters". However, many more stars are visible with even a modest telescope. Astronomers estimate that the cluster has approximately 500–1,000 stars, all of which are around 100 million years old. However, they vary considerably in type. The Pleiades themselves are represented by large, bright stars; also many small brown dwarfs and white dwarfs exist. The cluster is estimated to dissipate in another 250 million years. The Pleiades cluster is classified as a Shapley class c and Trumpler class I 3 r n cluster, indicating that it is irregularly shaped and loose, though concentrated at its center and detached from the star-field.
To the east, the two horns of the bull are formed by Beta Tauri and Zeta Tauri; two star systems that are separated by 8°. Beta is a white, spectral class B7 III giant star known as El Nath, which comes from the Arabic phrase "the butting", as in butting by the horns of the bull. At magnitude 1.65, it is the second brightest star in the constellation, and shares the border with the neighboring constellation of Auriga. As a result, it also bears the designation Gamma Aurigae. Zeta Tauri is an eclipsing binary star that completes an orbit every 133 days.
The star Lambda Tauri is an eclipsing binary star. This system consists of a spectral class B3 star being orbited by a less massive class A4 star. The plane of their orbit lies almost along the line of sight to the Earth. Every 3.953 days the system temporarily decreases in brightness by 1.1 magnitudes as the brighter star is partially eclipsed by the dimmer companion. The two stars are separated by only 0.1 astronomical units, so their shapes are modified by mutual tidal interaction. This results in a variation of their net magnitude throughout each orbit.
Located about 1.8° west of Epsilon Tauri is T Tauri, the prototype of a class of variable stars called T Tauri stars. This star undergoes erratic changes in luminosity, varying between magnitude 9 to 13 over a period of weeks or months. This is a newly formed stellar object that is just emerging from its envelope of gas and dust, but has not yet become a main sequence star. The surrounding reflection nebula NGC 1555 is illuminated by T Tauri, and thus is also variable in luminosity. To the north lies Kappa Tauri, a visual double star consisting of two A7-type components. The pair have a separation of just 5.6 arc minutes, making them a challenge to split with the naked eye.

Proper name	Designation	Light years	Apparent magnitude
Aldebaran	α Tauri	65	0.87
Elnath	β Tauri	131	1.65
Alcyone A	η Tauri	368	2.85
Tianguan	ζ Tauri	417	2.97
Chamukuy	θ Tauri	149	3.40
Sadr al Tauri	λ Tauri	370	3.41
Ain	ε Tauri	155	3.53
Omicron Tauri	ο Tauri	211	3.61
Atlas A	27 Tauri	380	3.62
Prima Hyadum	γ Tauri	154	3.65

Deep-sky objects

In the northern part of the constellation to the northeast of the Pleiades lies the Crystal Ball Nebula, known by its catalogue designation of NGC 1514. This planetary nebula is of historical interest following its discovery by German-born English astronomer William Herschel in 1790. Prior to that time, astronomers had assumed that nebulae were simply unresolved groups of stars. However, Herschel could clearly resolve a star at the center of the nebula that was surrounded by a nebulous cloud of some type. In 1864, English astronomer William Huggins used the spectrum of this nebula to deduce that the nebula is a luminous gas, rather than stars.

Identifier	Mag.	Object type
NGC 1514	10.9	planetary nebula
NGC 1647	6.4	open cluster
NGC 1746	6	asterism
NGC 1817	7.7	open cluster
NGC 1952	8.4	supernova remnant

North-west of ζ Tauri by 1.15 degrees is the Crab Nebula, a supernova remnant. This expanding nebula was created by a Type II supernova explosion, which was seen from Earth on July 4, 1054. It was bright enough to be observed during the day and is mentioned in Chinese historical texts. At its peak, the supernova reached magnitude −4, but the nebula is currently magnitude 8.4 and requires a telescope to observe. North American peoples also observed the supernova, as evidenced from a painting on a New Mexican canyon and various pieces of pottery that depict the event. However, the remnant itself was not discovered until 1731, when John Bevis found it.
This constellation includes part of the Taurus-Auriga complex, or Taurus dark clouds, a star-forming region containing sparse, filamentary clouds of gas and dust. This spans a diameter of and contains 35,000 solar masses of material, which is both larger and less massive than the Orion Nebula. At a distance of, this is one of the nearest active star forming regions. Located in this region, about 10° to the northeast of Aldebaran, is an asterism NGC 1746 spanning a width of 45 arcminutes.