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Acrux (Alpha Crucis) - HD108248 - HIP60718 - HR4730

Acrux (Alpha Crucis) is a blue subgiant star that can be located in the constellation of Crux. It is the 14th brightest star in the night sky. Alpha Crucis is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR4730. HIP60718 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD108248. Acrux is a multiple star system with 2 stars orbiting in its solar system.

Acrux is the southern most star of the constellationCrux, the Southern Cross. Although the picture below probably gives the impression it is the Northern most of the stars, the picture is the wrong way up. Acrux is one of the brightest stars in the night sky, coming in at position thirteen and being one of the most in the Southern hemisphere.

Location of Acrux

The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For Acrux, the location is 12h 26m 35.94 and -63d05`56.6 .

Proper Motion of Acrux

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -014.86 ± 000.36 towards the north and -035.83 ± 000.50 east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Acrux

Acrux has a spectral type of B0.5IV. This means the star is a blue subgiant star. The star has a B-V Colour Index of -0.24 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 21,255 Kelvin.

Acrux has been calculated as 4.74 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,299,945.35.km.

The star has a companion star which is in orbit close by, it has at least the following companions in close orbit, Acrux B.

Acrux Apparent and Absolute Magnitudes

Acrux has an apparent magnitude of 0.77 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of -4.19 If you used the 2007 Parallax value, you would get an absolute magnitude of -4.20. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to Acrux

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 10.17 which gave the calculated distance to Acrux as 320.71 light years away from Earth or 98.33 parsecs. In 2007, Hipparcos data was revised with a new parallax of 10.13 which put Acrux at a distance of 321.98 light years or 98.72 parsecs.

It would take a spaceship travelling at the speed of light, 320.71 years using the 1997 distance to get there. We don't have the technology or spaceship that can carry people over that distance yet.

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

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Acrux Facts

Alternative Names

Traditional NameAcrux
Bayer DesignationAlpha Crucis
Hipparcos Library I.D.60718
Yale Bright Star Catalogue (HR) Id4730
Henry Draper Designation108248

Visual Facts

Star Typesubgiant star
Absolute Magnitude-4.19 / -4.20
Apparent Magnitude0.77
Right Ascension (R.A.)12h 26m 35.94
Declination (Dec.)-63d05`56.6
1997 Distance from Earth10.17 Parallax (milliarcseconds)
 320.71 Light Years
 98.33 Parsecs
2007 Distance from Earth10.13 Parallax (milliarcseconds)
 321.98 Light Years
 98.72 Parsecs
Proper Motion Dec.-14.86 ± 0.36 milliarcseconds/year
Proper Motion RA.-35.83 ± 0.50 milliarcseconds/year
B-V Index-0.24
Spectral TypeB0.5IV
Brightest in Night Sky14th
Colour(B) blue

Companions (Multi-Star and Exoplanets) Facts

Stars in Solar System2
Companion StarsAcrux B

Estimated Facts

Radius (x the Sun)4.74
Calculated Effective Temperature21,255 Kelvin

Sources and Links

SIMBAD SourceLink

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
108248-62 2745.4A1.60000-25.00000-17.00000B1Blue/White
108249B2.10000-35.00000-7.00000B3Blue/White1955
108250-62 2742.4C5.10000-42.00000-22.00000B5Blue/White1826

Location of Acrux in Crux


Acrux (Alpha Crucis) Location in Crux

The map was generated using Night Vision, an awesome free application by Brian Simpson.



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