Achernar (Alpha Eridani) Star Facts

Achernar, also known as Alpha Eridani is a main sequence star located in the constellation of Eridanus, River Eridanus. Achernar is a major star and forms part of the constellation. Achernar is the traditional/proper name for the star, whilst Alpha Eridani is the Bayer Designation for the star. A list of additional names and identifications is in the facts list at the bottom of the page.

Based on the spectral type (B3Vp), Achernar colour is blue, which means that the star is one of the hottest stars in the Universe, hotter than our star.

Achernar temperature is in the range of 10,000 to 30,000 Kelvin. Based on the spectral type (B3Vp) as we don't have the exact temperature', we can deduce that the surface temperature of Achernar is in the order of 10,000 and 25,000K based on the notes from Harvard University. To put this in context, the temperature of our Sun is about 5,778 Kelvin as said by Google.

Achernar is the brightest star in Eridanus and the 9th in the night sky based on the Hipparcos 2007 apparent magnitude. Based on a parallax of 23.39, Achernar distance from Earth can be calculated at being 139.45 light years away or 44.09 parsecs.

Achernar is a naked-eye star, so you don't need a telescope or binoculars when you look up on a clear night. The lower the magnitude, the easier it will be to see it.

Achernar is an irregular variable star. Variable stars are stars whose size and/or brightness changes over time. Achernar brightness ranges from 0.459 (dimmest) to 0.398 over a period of 0.076 days.

Achernar Shape

Achernar is one of those rare stars in that it is not entirely spherical. Unlike the majority of stars, it's more egg-shaped. Other egg-shaped stars include Regulus and Vega. Its shape is caused by its spin and probably by its companion star pulling on it.

Achernar is at the southern end of its constellation and therefore is not visible to many northern hemispheric countries. However, given its proper motion, one day it will be seen as far north as England. At the other end of the constellation is the second brightest star Cursa, Beta Eridani.

Location

The location of the Achernar in the night sky is determined by the right ascension (R.A.) and declination (Dec.). These are equivalent to the Longitude and Latitude on Earth. The Right Ascension (Longitude) is expressed in time (hh:mm:ss) and is how far the star is along Earth's celestial equator. If the R.A. is positive, then it's eastwards and vice versa.

The Declination (Latitude) is how far north or south the object is compared to the celestial equator and is expressed in degrees. If the value is positive, it is north of the celestial equator. For Achernar, the location is 01h 37m 42.75 and -57° 14` 12.0 .

Based on the location of Eridanus, Achernar can be located in the equatorial region of the celestial sky. The celestial hemisphere is equivalent to the hemispheres on Earth. Being in the equatorial region, Achernar can be seen in both terrestrial hemispheres but there is a caveat of depending how far south and north you are. Achernar is south of the Ecliptic. The Ecliptic is the path that the Earth takes as it orbits the Sun. As the Earth is titled, we therefore have Celestial and Ecliptic hemispheres and they can be different for a star.

Physical Properties

Achernar Luminosity

Luminosity is the amount of energy a star pumps out relative to the amount that our star, the Sun, gives out. Our star, the Sun's value is 1. Achernar luminosity figure of 2,858.39 is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012. The star generates more energy than our star.

Achernar Size (Radius)

Achernar's is not spherical like the Sun, it more egg-shaped. At the thinnest point, it is 6.78 Solar Radii but at its widest, it is 9.16 times the radius of the Sun (Solar Radii). This star would be egg-shaped unlike a spherical shape like the Sun.

Magnitude (Apparent / Absolute / Visible)

A number represents a star’s magnitude, whether apparent/visual or absolute. The smaller the number, the brighter the star is. The Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Achernar apparent magnitude is 0.45, which is a measure of the star's brightness as seen from Earth. Apparent Magnitude is also known as Visual Magnitude.

If you use the 1997 parallax value, Achernar' absolute magnitude is -2.77. If you use the 2007 parallax value, Achernar' absolute magnitude is -2.70. Absolute Magnitude is the star's apparent magnitude from 10 parsecs or 32.6 light years. The magnitude assumes nothing is between the object and the viewer, such as dust clouds. To compare different stars' actual brightness, you would best use Absolute rather than Apparent Magnitude.

Achernar is visible from Earth without needing binoculars or a telescope. The lower the Apparent Magnitude of a star or other object is, the easier it is to see in the night sky. An object with a magnitude greater than 6.5 cannot be seen without a telescope or other device.

Achernar Fact List

The table is scrollable if you can't see everything, just swipe the table to see the hidden information.

Key Facts

Primary Name:

Spectral Type:

Star Type:

Colour:

Galaxy:

Constellation:

Celestial Hemisphere:

Main Star

Age

Visual / Apparent Magnitude

Visible From Earth

Absolute Magnitude

Radial Velocity

Eccentricity:

Semi-Major Axis

Luminosity (Lsun)

Mass (Solars)

Radius

Location/Coordinates

Right Ascension

Declination

Galactic Latitude

Galactic Longitude

Galacto-Centric Distance:

Distance from Earth

Parallax

Light Years

Parsecs

Astronomical Units (A.U.)

Proper Motion

Declination

Right Ascension

Miscellaneous Facts

B-V Index

Brightest in Night Sky

Variable Star Class

Variable Star Type

Mean Variability Period (Days)

Variable Magnitude Range

Alternate Names