Acrux / Alpha Crucis Star Facts (Type, Distance, Magnitude, Age, Mass, Colour, Location and more)

Acrux, also known as Alpha Crucis (Bayer) is a spectroscopic binary star located in the constellation of Crux, The Southern Cross. Acrux is a major star and forms part of the constellation.

Based on the spectral type (B0.5IV), Acrux colour is blue, which means that the star is one of the hottest stars in the Universe, hotter than our star.

Acrux temperature is in the range of 10,000 to 30,000 Kelvin. Based on the spectral type (B0.5IV) as we don't have the exact temperature', we can deduce that the surface temperature of Acrux 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.

Acrux is the brightest star in Crux and the 13th in the night sky based on the Hipparcos 2007 apparent magnitude. Based on a parallax of 10.13, Acrux distance from Earth can be calculated at being 321.98 light years away or 98.33 parsecs.

Acrux 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.

Location

The location of the Acrux 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 Acrux, the location is 12h 26m 35.94 and -63° 05` 56.6 .

Based on the location of Crux, Acrux can be located in the southern hemisphere of the celestial sky. The celestial hemisphere is equivalent to the hemispheres on Earth. Acrux 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

Spectral Type

Acrux spectral type of B0.5IV which means its colour and type is blue spectroscopic binary star. There is no relationship between colour and size. For example, a red star can be large or small. Small stars are more energy efficient than larger stars and live longer.

Acrux 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. Acrux luminosity figure of 30,302.96 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.

Acrux Size (Radius)

Acrux radius has been calculated as being 7.8 times bigger than the Sun. The Sun's radius is 695,800km, therefore, the Acrux radius is an estimated 5,427,240.km. If you need the star's diameter, you just need to multiply the radius by 2.

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.

Acrux apparent magnitude is 0.77, 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, Acrux' absolute magnitude is -4.19. If you use the 2007 parallax value, Acrux' absolute magnitude is -4.20. 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.

Acrux 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.