Universe Guide

Choo (Alpha Arae) Star Facts

Choo Facts

  • Choo is a eruptive main sequence star that can be located in the constellation of Ara. The description is based on the spectral class.
  • Choo is a main star of the constellation outline.
  • Based on the spectral type (B2Vne) of the star, the star's colour is blue .
  • 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.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 267.35 light years away from us. Distance

Choo's Alternative Names

Alpha Arae (Alf Ara) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

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 objects' alternative names can be found at Star Names .

Location of Choo

The location of the main sequence 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 object 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 .

Radial Velocity and Proper Motion of Choo

Proper Motion

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 milliarcseconds/year towards the north and -33.27 ± 0.85 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is 0.00000 km/s with an error of about 999.00 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties of Choo

Choo Colour and Temperature

Based on the star's spectral type of B2Vne , Choo's colour and type is blue main sequence star. The star has a B-V Colour Index of -0.13 which means the star's temperature is about 12,762 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

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.

Choo Radius

Choo estimated 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 4.2372384989493488634317029248. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It 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 13.46000 which gave the calculated distance to Choo as 242.32 light years away from Earth or 74.29 parsecs. If you want that in miles, it is about 1,424,508,500,429,852.38, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 12.20000 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.

Using the 2007 distance, the star is roughly 16,907,408.36 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun. 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*.

Travel Time to Choo

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Airbus A380736243,599,668.16
Speed of Sound (Mach 1)767.269233,672,096.44
Concorde (Mach 2)1,534.54116,835,895.94
New Horizons Probe33,0005,433,010.78
Speed of Light670,616,629.00267.35

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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Additional Choo Facts and Figures

Visual Facts

Primary / Proper / Traditional NameChoo
Alternative NamesAlpha Arae, Alf Ara, HD 158427, HIP 85792, HR 6510, alf Ara
Spectral TypeB2Vne
Constellation's Main StarYes
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
GalaxyMilky Way
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-8.82716503 degrees
Galactic Longitude340.75537387 degrees
1997 Distance from Earth13.46000 Parallax (milliarcseconds)
 242.32 Light Years
 74.29 Parsecs
2007 Distance from Earth12.20000 Parallax (milliarcseconds)
 267.35 Light Years
 81.97 Parsecs
 16,907,408.36 Astronomical Units
Galacto-Centric Distance23,888.20 Light Years / 7,324.00 Parsecs
Proper Motion Dec.-67.22000 ± 0.36000 milliarcseconds/year
Proper Motion RA.-33.27000 ± 0.85000 milliarcseconds/year
B-V Index-0.13
Radial Velocity0.00000 ± 999.00 km/s
Semi-Major Axis6469.0000000
Stellar Luminosity (Lsun)971.4800000

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 Calculated Facts

Radius (x the Sun)4.24
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

Location of Choo in Ara

Choo Location in Ara

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

Ara Main Stars

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