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Choo, Alpha Arae, HD158427, HIP85792, HR6510

Choo (Alpha Arae) Location in Ara

Choo (Alpha Arae) is a blue eruptive main sequence dwarf star that can be located in the constellation of Ara. The description is based on the spectral class. Choo is the 1st brightest star in Ara based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Choo's Alternative Names

Alpha Arae (Alf Ara) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR6510. HIP85792 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD158427.

Choo has alternative name(s) :- , alf Ara.

More details on star alternative names can be found at Star Names .

Location of Choo

The location of the star in the night sky 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 Choo, the location is 17h 31m 50.52 and -49° 52` 33.5 .

Proper Motion of Choo

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 -67.22 ± 0.36 miliarcseconds/year towards the north and -33.27 ± 0.85 miliarcseconds/year east if we saw them in the horizon. The Radial Velocity, that is the speed at which the star is moving away/towards us is 0.00000 km/s with an error of about 999.00 km/s .

Choo Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 971.48 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of Choo

Choo has a spectral type of B2Vne. This means the star is a blue main sequence dwarf star. The star is 7,324.00 Parsecs from the Galactic Centre or terms of Light Years is 23,888.20 s. The star has a B-V Colour Index of -0.13 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 12,762 Kelvin.

Choo Radius has been calculated as being 3.83 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,664,189.88.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 4.24. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Choo Apparent and Absolute Magnitudes

Choo has an apparent magnitude of 2.84 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 -1.51 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.73. 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 Choo

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 13.46 which gave the calculated distance to Choo as 242.32 light years away from Earth or 74.29 parsecs. It would take a spaceship travelling at the speed of light, 242.32 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

In 2007, Hipparcos data was revised with a new parallax of 12.20 which put Choo at a distance of 267.35 light years or 81.97 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

The star's Galacto-Centric Distance is 7,324.00 Parsecs or 23,888.20 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Choo

The star is a eruptive Gamma Cassiopeiae variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. Choo brightness ranges from a magnitude of 2.821 to a magnitude of 2.739 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 days (variability).

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 Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

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Choo Facts

Visual Facts


Primary / Proper / Traditional NameChoo
Alternative NamesAlpha Arae, Alf Ara, HD 158427, HIP 85792, HR 6510, alf Ara
Spectral TypeB2Vne
Multiple Star SystemYes
Star Type main sequence Dwarf Star
Colour blue
GalaxyMilky Way
ConstellationAra
Absolute Magnitude-1.51 / -1.73
Visual / Apparent Magnitude2.84
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)17h 31m 50.52
Declination (Dec.)-49° 52` 33.5
Galactic Latitude-8.83 degrees
Galactic Longitude340.76 degrees
1997 Distance from Earth13.46 Parallax (milliarcseconds)
 242.32 Light Years
 74.29 Parsecs
2007 Distance from Earth12.20 Parallax (milliarcseconds)
 267.35 Light Years
 81.97 Parsecs
Galacto-Centric Distance23,888.20 Light Years / 7,324.00 Parsecs
Proper Motion Dec.-67.22 ± 0.36 milliarcseconds/year
Proper Motion RA.-33.27 ± 0.85 milliarcseconds/year
B-V Index-0.13
Radial Velocity0.00 ± 999.00 km/s
Eccentricity0.13
Semi-Major Axis6469.00
Stellar Luminosity (Lsun)971.48

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEruptive
Variable Star TypeGamma Cassiopeiae
Mean Variability Period in Days0.070
Variable Magnitude Range (Brighter - Dimmer)2.739 - 2.821

Estimated Facts


Calculated Effective Temperature12,762 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
158427-4911511.2A3.00000-24.00000-71.00000B3Blue/White
B11.000001913

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