Capella (Alpha Aurigae)

Capella (Alpha Aurigae) is a star in the constellation Auriga, magnitude 0.1.

One golden point, four stars — two yellow giants locked in a 104-day embrace and a distant pair of red dwarfs.

To the eye Capella is one star. It is really four. Most of its light comes from two yellow giants, each about two and a half times the Sun’s mass, whirling round each other every 104 days — barely farther apart than Venus is from the Sun. Both have used up the hydrogen in their cores and swollen; the larger is about 12 times the Sun’s width. Far beyond them travels a second pair: two faint red dwarfs.

Its name is Latin for ‘little she-goat’: the goat Amalthea, who suckled the infant Zeus. Goat lore around these stars goes back to Mesopotamia, and Bedouin astronomers saw Auriga as a herd of goats. In classical times it was seen as a portent of rain.

In 1899 William Wallace Campbell at Lick Observatory saw two sets of spectral lines swinging back and forth in its light, proving it was a double.

Capella (Alpha Aurigae) is 43 light-years away: the light we see from it set off in 1983, 7 years before the Hubble Space Telescope was launched.

Did you know?

• The interferometrist’s friend. In 1919 John Anderson and Francis Pease split Capella’s giants with an interferometer at Mount Wilson — the first interferometric measurement of any object beyond the Solar System.
• A star that shines in X-rays. Capella is one of the brightest X-ray sources in the sky. Rocket flights picked it up in 1962 and 1963; the X-rays come mainly from the hot corona of one of the giants.
• Aligned with a temple. Building J at Monte Albán in Mexico, built around 275 BC, faces the point where Capella rose. Its first dawn rising came within a day of the Sun passing directly overhead there.

A bright golden-yellow star, the first-magnitude star closest to the north celestial pole, at the corner of Auriga’s pentagon. Find it about halfway between Orion’s Belt and Polaris. Beside it, a small triangle of fainter stars marks the Kids.

What is a star?

When and where to see it

It is best placed in the evening sky around January, when it crosses the meridian at about 10 pm local time (around midnight in December). It can be seen from everywhere north of 44°S and never sets north of 44°N.

At its highest it stands 86° up from 50°N, 79° up from 35°N, 44° up from the equator, 9° up from 35°S.

Facts

Type

Star

Constellation

Auriga

Designations

Alpha Aurigae, Goat Star, α Aur, 13 Aur, HR 1708, HD 34029, HIP 24608

Magnitude

0.1

Position

RA 5h 16.7m, Dec +45° 60′ (J2000)

Spectral type

G3III:

Colour

yellow (B−V 0.80)

Distance

43 light-years

Discovered

Known since antiquity

Open AstroPilot to see when Capella (Alpha Aurigae) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.