Taurus (constellation)

Taurus or Taurus is a zodiacal constellation; Its Latin name is Taurus and in Spanish toro. It stands out in the winter sky, between Aries to the west and Gemini to the east. To the north are Perseus and Auriga; to the southeast Orion, and to the southwest Eridanus and Cetus.

In the zodiac it is the second sign. As such, in Antiquity it contained the constellation of the same name, but the precession of the equinoxes has meant that the sign of Taurus is occupied by the constellation of Aries. Currently the sun shines on Taurus between May 14 and June 21.

Notable features

Constellation of Taurus AlltheSky.com

Aldebaran (α Tauri), the constellation's brightest star, is an orange giant —cataloged as K5+III— of first magnitude. The name Aldebaran comes from the Arabic الدبران, meaning "the one that follows", referring to the fact that this star follows the Pleiades cluster on its nightly journey through the sky. Being close to the ecliptic, Aldebaran is periodically hidden by the Moon and, thanks to this, it has been possible to measure its angular diameter to assess its true diameter, which is 44 times greater than that of the Sun. It is classified as an irregular pulsating variable, with a brightness fluctuation of 0.2 magnitudes. It forms a binary system with a faint red dwarf: the current separation between the two stars is 607 au.

Elnath or Alnath (β Tauri), the second brightest star, forms the bull's horns together with ζ Tauri. The first is a bluish-white giant of spectral type B7III with a luminosity 700 times greater than solar luminosity. It is a mercury-manganese star with anomalous contents of some metals. For its part, ζ Tauri, officially called Tianguan, is an eclipsing binary with an orbital period of 0.36 years. The main component is a rapidly rotating bluish-white subgiant (330 km/s), being one of the most studied Be stars. The disk of matter around the star—whose angular diameter has been directly measured—has a diameter 64 times the diameter of the Sun.

Another eclipsing binary is λ Tauri, formed by a blue main-sequence star of type B3V and a white subgiant of type A4IV very close to each other, barely 0.10 au apart—27% of the distance from Mercury and the Sun. As the white star is less luminous than the blue one, when the former passes in front of the latter every 3.95 days, the brightness of λ Tauri decreases by 0.7 magnitudes.

ξ Tauri is a multiple star made up of a triple star orbited by a fourth component. The triple star is formed by a close binary —also an eclipsing binary— made up of two bluish-white stars of type B9V whose period is 7.15 days. Around this inner pair moves a B8V star that takes 145 days to complete its orbit. The fourth component is of the eighth magnitude and is visually several tenths of an arc second from the triple star.

Nebula NGC 1555 illuminated by the star T Tauri

Two variable stars in the constellation, T Tauri and RV Tauri, are the prototypes for groups of stars that bear their names. Thus, T Tauri stars are young stars that have not yet entered the main sequence, are close to molecular clouds, and are variable: examples of this class are CoKu Tauri/4, which is only 1 million years old, and AA Tauri, surrounded by a protoplanetary disk in which the presence of hydrogen cyanide, acetylene, and carbon dioxide have been detected. Similarly, DG Tauri is another T Tauri star where two x-ray jets have been imaged extending about 700 au in both directions from the star. For their part, the RV Tauri variables are type G, F or K supergiants whose luminosity changes are linked to radial pulsations on their surfaces; changes in brightness are accompanied by changes in spectral type.

RR Tauri is a Herbig Ae/Be star—equivalent to a T Tauri star but more massive and hot—of type A0:IVe. It is characterized by its violent variability in the visible spectrum, since the full range of variation it ranges from magnitude 10.6 to magnitude 13.8-14.0. Furthermore, the fluctuations take place on time scales as short as one day and are completely unpredictable.

Another variable of interest is IK Tauri, an oxygen-rich giant asymptotic branch star with a surface temperature of 2200 K. It is a Mira variable whose brightness varies between magnitude 10.8 and 16.5 over a period of 470 days. Likewise, CE Tauri is a red supergiant cataloged as a semiregular variable whose radius is 590 times greater than the solar radius.

Planetary systems have been discovered in several stars of the constellation. HD 37124 is a subgiant or yellow dwarf of type G4IV-V with three exoplanets located at 0.5, 1.7 and 2.8 AU from the star. Another G5IV type subgiant, HD 32963, is orbited by a planet at a distance of 3.41 AU. Hoggar, name of HD 28678, is another star with a planet whose mass is at least 70% greater than that of Jupiter. CI Tauri, a 2-million-year-old young star of spectral type K4IVe, also hosts a planetary system with a "hot Jupiter" planet, which is surprising for such a young star. Instead, Gliese 176 is a red dwarf 31 light-years away, where in 2008 the existence of a planet yet to be confirmed was announced.

Image of the Crab Nebula obtained with the Hubble Space Telescope.

Taurus also contains two of the best-known open clusters in the sky. The first of them, the Pleiades (M45), is one of the closest stellar clusters to Earth and its main components —including Alcíone, the brightest, or Atlas— are hot blue stars that have formed in the last hundred million years. The cluster contains more than 1,000 confirmed members, although this number does not include unresolved binary systems. Although the cluster's distance has been the subject of some controversy, the most recent studies place it at 136 parsecs (444 light-years) from the solar system.

The other cluster, the Hyades, consists of 80 stars and is 153 light-years away, making it the closest star cluster to Earth. While the cluster is about 75 light-years across, the prominent central group is about 10 light-years across. His Hertzsprung-Russell diagram indicates that the Hyades are 625 ± 50 million years old and the five brightest members of this cluster—including γ Tauri and θ2 Tauri—are already evolving into giant stars. One of these giants, ε Tauri or Ain, has spectral type G9.5III and has a massive extrasolar planet —its mass is at least 7.6 times that of Jupiter— orbiting 1.93 AU from it.

The Crab Nebula (M1) is located in this constellation. It is the supernova remnant from a supernova explosion in 1054 (SN 1054). It is about six light-years in radius and lies at a distance of approximately 6,500 light-years from Earth. At its center is the Crab Pulsar (PSR B0531+21); its period of rotation is 33 milliseconds and it emits pulses of radiation ranging from gamma rays to radio waves. Another supernova remnant —on the border with Auriga— is Simeis 147, one of the oldest of its kind, since its age is estimated at around 100,000 years.

Infrared image of the Merope Nebula, distant 440 light years

NGC 1514 is a planetary nebula, discovered by William Herschel in 1790, in whose center there is a binary star with a period that can be between 4 and 9 days. The star that gave rise to the nebula is today invisible, the companion being a giant of type A0III. It has been speculated that the nebula comes from a common envelope for both stars.

NGC 1435 or Merope Nebula is a diffuse reflection nebula in the Pleiades illuminated by the star of the same name, type B6IV(e). Although in the past it was thought that the Pleiades formed from this and other nebulae bordering, today it is accepted that the nebulosity is the result of a fortuitous encounter with the cloud.

Another reflection nebula is NGC 1555 —also called Hind's Nebula—, in this case illuminated by the star T Tauri. Both the star and the nebula vary significantly in brightness, but not necessarily at the same time. Since T Tauri is part of a multiple system, it has been suggested that this nebula may also contain another very young stellar object.

NGC 1409 and NGC 1410 are two colliding galaxies observable in Taurus. The two are connected by what appears to be a gas pipeline that extends over 20,000 light-years.

Main Stars

Comparative sizes of Aldebaran and the Sun.

The Pleiades.

• α Tauri (Aldebaran), giant red-orange star of magnitude 0.87. It has a tenuous companion of magnitude 13.5 to 28 seconds of arc.
• β Tauri (Elnath), white-azulada giant of magnitude 1.68.
• γ Tauri (Hyadum I), an orange giant member of the Híades cluster of magnitude 3.65.
• δ Tauri, actually three stars, all members of the Hydes. δ¹ Tauri (Hyadum II) is a star similar to Hyadum I.
• ε Tauri (Ain), a yellow-orange giant member of the Híades with magnitude 3.53 and where an extrasolar planet has been discovered.
• ج Tauri, a 2,97-scale binary star in the southern horn of the bull.
• η Tauri (Alcíone), the brightest star of the Pleiades cluster and the third of the constellation with magnitude 2.85, is a young white-smoky star.
• θ Tauri, name of Bayer shared by two different stars, θ1 Tauri and θ2 Tauri; orange and white, respectively, are separated 5.6 minutes of arc and are part of the Híades.
• κ Tauri, a visual double star whose components, white, are separated 5.6 minutes of arc.
• λ Tauri, triple star system and eclipsing variable.
• ν Tauri, white star of the main sequence of magnitude 3.90.
• ・ Tauri, quadruple star system of magnitude 3.73.
• ο Tauri and π Tauri, yellow giants of magnitude 3.62 and 4.69 respectively.
• ρ Tauri, variable Delta Scuti of magnitude 4,66.
• ω2 Tauri, star Am of magnitude 4,93.
• n Tauri (109 Tauri), a yellow giant of magnitude 4,96.
• Merope (23 Tauri), star of the Pleiades that illuminates the nebula of reflection NGC 1435.
• 10 Tauri, yellow star located at 45 light years with a possible circumestelar disk around it.
• 30 Tauri (e Tauri), young binary star of magnitude 5,06 with an estimated age of less than 28 million years.
• 39 Tauri, yellow dwarf somewhat colder than the Sun of magnitude 5.90.
• 79 Tauri, star of the Hydes surrounded by a disc of circumestelar dust.
• 90 Tauri (c Tauri), a white star of magnitude 4,27 that is part of the Hides.
• 111 Tauri, yellow dwarf at 48 light years of the solar system.
• 139 Tauri, light blue giant of magnitude 4,82.
• T Tauri, prototype variable star of a class of stars in formation process and have not yet entered the main sequence.
• And Tauri, carbon star and semi-regular variable whose brightness varies between magnitude 6.5 and 9.2 in a period of 241.5 days.
• RV Tauri, prototype of intermediate variable stars between the cefeides and the Mira variables.
• RZ Tauri, an eclipsing contact binary where mass transfer occurs between the two stars.

Image of DG Tauri obtained with the Chandra X-ray observatory.

• UX Tauri, three-star T Tauri system; around the brightest a protoplanetary disk has been discovered.
• AA Tauri, T Tauri star that has a protoplanetary disk in which organic molecules have been detected.
• CD Tauri, a multi-dimensional binary of magnitude 6.77.
• CE Tauri (119 Tauri), red supergiant, one of the biggest stars known.
• DG Tauri, T Tauri star where two X-ray jets have been observed.
• EQ Tauri, contact binary of magnitude 11,20.
• IK Tauri (NML Tauri), one of the stars of the giant asymptotic branch most studied; it is a Mira variable whose brightness ranges between magnitude 10.8 and 16.5.
• HD 37124, yellow star with three known planets.
• Gliese 176 (HD 285968), red dwarf with a super-tiered extrasolar planet.
• CoKu Tauri/4, young T Tauri star surrounded by a circum-stellar disk.
• Gliese 169, distant orange dwarf 37.5 light years.
• HL Tau 76 (V411 Tauri), pulsating white dwarf, variable type ZZ Ceti.

Deep Sky Objects

M1 (Crab nebula).

• The Pleiades (M45) is an open cluster of stars located north of the constellation. The cluster is about twelve light years in diameter and contains a total of 500 to 1000 stars. It is dominated by young blue stars, of which eight can be observed at a glance depending on the atmospheric conditions (very clean heavens and Moon's absence). Inside it is the Merope nebula (NGC 1435).
• The Híades is also an open cluster that helps form the "V" in the sky that forms the beginning of the bull's head. It is 153 light years away and consists of 80 stars located in a sphere of 12 squares in diameter.
• M1 or Crab nebula, formed by the remains of a supernova whose explosion, observed on Earth on July 4, 1054, was bright enough to see it day. It is mentioned in Chinese chronicles and in Amerindian poetry. Inside is a pulp — a very dense neutron star that rotates at high speed — called Crab Pulsar. It is approximately 25 km in diameter and broken at a rate of 30 times per second.
• NGC 1514, planetary nebula about 600 light years away.
• NGC 1555, nebula of reflection that experiences variations in its brightness as a result of changes in the star that illuminates it (T Tauri).
• Simeis 147, dim nebula originated by a supernova over 100,000 years ago.
• NGC 1410 and NGC 1409, two galaxies interacting with each other.

Mythology

Taurus Constellation "The Bull."

In Greek mythology, Taurus is the bull form that the god Zeus took to seduce Europa, a mythical Phoenician princess. They had three sons: Minos, the legendary king of Crete, Sarpedon, and Radamantis.

Another version tells us that it was the beast that the goddess Hera sent to kill Orion.

According to another version, Taurus is Io turned into a cow by her lover Zeus to prevent Hera from finding out about their love affairs.

According to another, it is the Bull of Crete.

Text references

General references

• _ Catasterism (Καταστερισμο).
  • 14: Toro (τα;ρος; Taurus): the bull in which Zeus was transformed to rapture Europe, or Io transformed into a cow.
  • Latin text in Google Books; electronic facsimile.
  • Greek text on the Internet Archive; electronic facsimile.

• HIGINO: Poetry astronomy (Astronomica).
  • 21: Toro.
    • English text on Mary Grant's Theoi site; 1960 trad.