# Aludra (Eta Canis Majoris)

Aludra (Eta Canis Majoris) is a star in the constellation Canis Major, magnitude 2.5.

**The Great Dog’s tail — a blue supergiant that has probably already been a red one.**

Aludra comes from the Arabic al-adhraa, “the virgin”. Arab astronomers grouped it with three neighbours in Canis Major — Adhara, Wezen and Omicron² — as the Virgins.

It has packed a whole life into less than 10 million years. Born with about 22 times the Sun’s mass, Aludra probably swelled into a red supergiant and has since shrunk back, shedding much of its mass along the way. Now a blue supergiant some 54 times the Sun’s width and over 100,000 times as luminous, it is in the final stages of its life.

It is still losing about one solar mass every 8.3 million years to its wind, and it varies slightly over 4.7 days, an Alpha Cygni [variable star](https://astropilot.space/glossary/variable-star). Since 1943 its spectrum has been the standard for its [spectral class](https://astropilot.space/glossary/spectral-type), the B5 supergiants.

Aludra (Eta Canis Majoris) is 2,000 light-years away: the light we see from it set off around AD 30, around the time Vesuvius buried Pompeii.

## Did you know?

- **Bow and Arrow.** In Chinese astronomy it is Hú Shǐ èr, the Second Star of the Bow and Arrow, an asterism drawn from stars of Canis Major and Puppis.
- **Two ships.** Two US Navy vessels, a stores ship and a cargo ship, were named USS Aludra after the star.

A blue-white 2nd-magnitude star at the tip of the Great Dog’s tail, the easternmost of a bright triangle it forms with Wezen and Adhara, south-east of Sirius.

## When and where to see it

It is best placed in the evening sky around February, when it crosses the meridian at about 10 pm local time (around midnight in January). It can be seen from everywhere south of 61°N and never sets south of 61°S.

At its highest it stands 11° up from 50°N, 26° up from 35°N, 61° up from the equator, 84° up from 35°S.

## Facts

- Type: Star
- Constellation: Canis Major
- Designations: Eta Canis Majoris, η CMa, 31 CMa, HR 2827, HD 58350, HIP 35904
- Magnitude: 2.5
- Position: RA 7h 24.1m, Dec −29° 18′ (J2000)
- Spectral type: B5Ia
- Colour: white (B−V -0.08)
- Distance: 2,000 light-years
- Discovered: Known since antiquity

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