What kind of star is Achernar?
Achernar, catalogued as Alpha Eridani (α Eri), appears in the official constellation Eridanus. Its apparent visual magnitude is about 0.46; variable, while its estimated distance is about 139 light-years. Astronomers classify the object as B6 Vep; binary system. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
The coordinate pair RA 01h 37m 42.85s, Dec −57° 14′ 12.3″ fixes the object’s direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
The name Achernar
From Arabic ākhir al-nahr, “the end of the river,” describing its position at the southern end of Eridanus.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Achernar
From southern latitudes, trace winding Eridanus away from Orion toward its brilliant endpoint. Northern observers need both a low clear southern horizon and a location below the star’s geographic visibility limit.
Predominantly southern; invisible north of about 33° N and circumpolar south of about 33° S. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Interesting facts about Achernar
- Achernar is among the ten brightest stars in the night sky.
- Extreme rotation produces a strongly oblate star with a much wider equator than polar diameter.
- It is a Be star: expelled material can form a gaseous equatorial disc and create emission lines.
- Interferometry made Achernar a landmark directly measured example of rotational flattening.
- A detected stellar companion means Achernar is not an isolated star.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values.