# Alioth (Epsilon Ursae Majoris)

Alioth (Epsilon Ursae Majoris) is a star in the constellation Ursa Major, magnitude 1.8.

**The brightest star of the Plough — a magnetic star whose strange spectrum shifts every five days.**

Alioth hides an odd personality behind its plain white light. It is a ‘peculiar’ A-type [star](https://astropilot.space/glossary/star) whose magnetic field — 100 times stronger than Earth’s — sorts the elements in its atmosphere into patches, including a dark band of chromium. Its magnetic poles lie almost at right angles to its spin axis, so as the star turns every 5.1 days, different patches swing into view and its spectral lines shift and change.

In 2008 a study suggested the five-day rhythm came from a hidden companion about 15 times Jupiter’s mass. Astronomers now think it is simply the star’s rotation, and no companion has been found. Alioth belongs to the Ursa Major moving group, a loose family of stars, including most of the Plough, that travel through space together.

Its name comes from the Arabic alyat al-hamal, ‘the sheep’s fat tail’. In India it was Añgiras, one of the Seven Rishis.

Alioth (Epsilon Ursae Majoris) is 83 light-years away: the light we see from it set off in 1943, 13 years after Pluto was discovered.

## Did you know?

- **The jade sighting-tube.** In China Alioth is the fifth star of the Northern Dipper, and is also called Yù Héng, the Star of the Jade Sighting-Tube.
- **A sailor’s star.** Alioth is one of the 57 navigational stars, and was long used by sailors in the maritime trade to fix their position at sea.

The brightest star of the Plough (Big Dipper), the first star of the handle next to the bowl. Compare it with Dubhe at the bowl’s outer corner: they are almost equally bright, but Dubhe is yellow-orange and Alioth white.

## When and where to see it

It is best placed in the evening sky around May, when it crosses the meridian at about 10 pm local time (around midnight in April). It can be seen from everywhere north of 34°S and never sets north of 34°N.

At its highest it stands 84° up from 50°N, 69° up from 35°N, 34° up from the equator, below the horizon from 35°S.

## Facts

- Type: Star
- Constellation: Ursa Major
- Designations: Epsilon Ursae Majoris, ε UMa, 77 UMa, HR 4905, HD 112185, HIP 62956
- Magnitude: 1.8
- Position: RA 12h 54.0m, Dec +55° 58′ (J2000)
- Spectral type: A1III-IVpkB9
- Colour: white (B−V -0.02)
- Distance: 83 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Alioth (Epsilon Ursae Majoris) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/alioth