Aldebaran (Alpha Tauri)
Aldebaran (Alpha Tauri) is a star in the constellation Taurus, magnitude 0.9.
The Bull’s fiery eye — an orange giant that only pretends to belong to the Hyades.
Aldebaran is a star in its final stages. More than six billion years old, it has used up the hydrogen in its core and swollen to about 45 times the Sun’s width, though it has only a little more mass. Its surface has cooled to about 3,900 K — the source of its orange glow — yet its sheer size lets it pour out over 400 times the Sun’s light. It turns slowly, once every 520 days.
Its name is Arabic for ‘the follower’: it seems to chase the Pleiades across the sky. It sits right in front of the Hyades star cluster, but is unrelated and far older. A faint companion star, far too dim for the eye, travels with it.
Its long history of measurements made it one of the benchmark stars used to calibrate the Gaia mission, and it was used before that to calibrate instruments on the Hubble Space Telescope.
Aldebaran (Alpha Tauri) is 67 light-years away: the light we see from it set off in 1959, around the time Sputnik became the first artificial satellite.
Did you know?
- The star that moved. Edmond Halley studied a record of the Moon covering Aldebaran, seen in Athens in AD 509. In 1718 he concluded the star had shifted since then — one of the clues that led him to discover that stars move.
- Hidden by the Moon. Aldebaran lies close to the Moon’s path, so the Moon sometimes passes in front of it in an occultation. A run of 49 such occultations took place between 2015 and 2018.
- Once the brightest. Between 420,000 and 210,000 years ago Aldebaran was the brightest star in our sky, peaking at magnitude −1.54.
A bright orange star, the eye of Taurus, at one tip of the V-shaped Hyades cluster. Follow Orion’s Belt away from Sirius to reach it. Compare its warm colour with the white stars of the V — it is not a member, just much nearer.
When and where to see it
It is best placed in the evening sky around December, when it crosses the meridian at about 10 pm local time (around midnight in December). It can be seen from everywhere north of 73°S and never sets north of 73°N.
At its highest it stands 57° up from 50°N, 72° up from 35°N, 73° up from the equator, 38° up from 35°S.
Facts
- Type
- Star
- Constellation
- Taurus
- Designations
- Alpha Tauri, Bull's Eye, α Tau, 87 Tau, HR 1457, HD 29139, HIP 21421
- Magnitude
- 0.9
- Position
- RA 4h 35.9m, Dec +16° 31′ (J2000)
- Spectral type
- K5+III
- Colour
- orange-red (B−V 1.54)
- Distance
- 67 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Aldebaran (Alpha Tauri) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.