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Altair (Alpha Aquilae) - HD187642 - HIP97649 - HR7557

Altair (Alpha Aquilae) is a blue eclipsing binary system subgiant star that can be located in the constellation of Aquila. It is the 13th brightest star in the night sky. Alpha Aquilae is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR7557. HIP97649 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD187642. The Id of the star in the Gould Star Catalogue is 86. Stars in the southern hemisphere are more likely to have a Gould Id than the northern hemisphere. For example, there are no Gould classified stars in Ursa Major. Altair has alternative name(s), 53 Aquilae , 53 Aql. In Arabic, it is known as At-Ta'ir.

Location of Altair

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 Altair, the location is 19h 50m 46.68 and +08d52`02.6 .

Proper Motion of Altair

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 385.29 ± 0.32 miliarcseconds/year towards the north and 536.23 ± 0.57 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Altair

Altair has a spectral type of A7IV-V. This means the star is a blue subgiant star. The star has a B-V Colour Index of 0.22 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 7,650 Kelvin.

Altair has been calculated as 1.92 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,336,728.67.km.

Altair Apparent and Absolute Magnitudes

Altair has an apparent magnitude of 0.76 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 2.21 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.21. 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 Altair

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 194.44 which gave the calculated distance to Altair as 16.77 light years away from Earth or 5.14 parsecs. It would take a spaceship travelling at the speed of light, 16.77 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 194.95 which put Altair at a distance of 16.73 light years or 5.13 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.

Variable Type of Altair

The star is a eclipsing binary system Beta Persei (Algol) 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. Altair brightness ranges from a magnitude of 1.000 to a magnitude of 1.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 8.0 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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Altair Facts

Alternative Names

Traditional/Proper NameAltair
Short Name53 Aql
Arabic NameAt-Ta'ir
English Meaning'The flying' eagle
Bayer DesignationAlpha Aquilae
Alternative Name(s)53 Aquilae
Hipparcos Library I.D.97649
Yale Bright Star Catalogue (HR) Id7557
Bonner DurchmusterungBD+08 4236
Gould I.D.86
Henry Draper Designation187642

Visual Facts

Star Typesubgiant star
Absolute Magnitude2.21 / 2.21
Apparent Magnitude0.76
Right Ascension (R.A.)19h 50m 46.68
Declination (Dec.)+08d52`02.6
1997 Distance from Earth194.44 Parallax (milliarcseconds)
 16.77 Light Years
 5.14 Parsecs
2007 Revised Distance from Earth194.95 Parallax (milliarcseconds)
 16.73 Light Years
 5.13 Parsecs
Proper Motion Dec.385.29 ± 0.32 milliarcseconds/year
Proper Motion RA.536.23 ± 0.57 milliarcseconds/year
B-V Index0.22
Spectral TypeA7IV-V
Brightest in Night Sky13th
Colour(A) blue

Variable Star Details

Variable Star ClassEclipsing binary system
Variable Star TypeBeta Persei (Algol)
Mean Variability Period in Days8.000

Estimated Facts

Radius (x the Sun)1.92
Calculated Effective Temperature7,650 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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
187642+08 4236.0A0.90000537.00000387.00000A5White
+08 4232.0B9.600009.00000-16.000001925
+08 4238.0C10.100001959

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