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Alphard (Alpha Hydrae) - HD81797 - HIP46390 - HR3748

Alphard (Alpha Hydrae) is a orange to red giant star that can be located in the constellation of Hydra. It is the 48th brightest star in the night sky. Alpha Hydrae is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR3748. HIP46390 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD81797. The Id of the star in the Gould Star Catalogue is 140. 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. Alphard has alternative name(s), 30 Hydrae , 30 Hya. In Arabic, it is known as Al-Fard.

Location of Alphard

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 Alphard, the location is 09h 27m 35.25 and -08d39`31.3 .

Proper Motion of Alphard

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 34.37 ± 0.11 miliarcseconds/year towards the north and -15.23 ± 0.18 miliarcseconds/year east if we saw them in the horizon.

Alphard 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 58.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of Alphard

Alphard has a spectral type of K3III. This means the star is a orange to red giant star. The star has a B-V Colour Index of 1.44 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,093 Kelvin.

Alphard has been calculated as 40.44 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 28,139,795.21.km.

Alphard Apparent and Absolute Magnitudes

Alphard has an apparent magnitude of 1.99 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 -1.69 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.72. 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 Alphard

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 18.40 which gave the calculated distance to Alphard as 177.26 light years away from Earth or 54.35 parsecs. It would take a spaceship travelling at the speed of light, 177.26 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 18.09 which put Alphard at a distance of 180.30 light years or 55.28 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.

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.

Alphard Facts

Alternative Names

Traditional/Proper NameAlphard
Short Name30 Hya
Arabic NameAl-Fard
English MeaningThe solitary one
Bayer DesignationAlpha Hydrae
Alternative Name(s)30 Hydrae
Hipparcos Library I.D.46390
Yale Bright Star Catalogue (HR) Id3748
Bonner DurchmusterungBD-08 2680
Gould I.D.140
Henry Draper Designation81797

Visual Facts

Star Typegiant star
Absolute Magnitude-1.69 / -1.72
Apparent Magnitude1.99
Right Ascension (R.A.)09h 27m 35.25
Declination (Dec.)-08d39`31.3
1997 Distance from Earth18.40 Parallax (milliarcseconds)
 177.26 Light Years
 54.35 Parsecs
2007 Revised Distance from Earth18.09 Parallax (milliarcseconds)
 180.30 Light Years
 55.28 Parsecs
Proper Motion Dec.34.37 ± 0.11 milliarcseconds/year
Proper Motion RA.-15.23 ± 0.18 milliarcseconds/year
B-V Index1.44
Spectral TypeK3III
Brightest in Night Sky48th
Colour(K) Orange to Red

Estimated Facts

Radius (x the Sun)40.44
Luminosity (x the Sun)58.0000000
Calculated Effective Temperature4,093 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
81797-08 2680.0A2.20000-18.0000028.00000K2Orange
-08 2681.0B9.700001841
C1783

Location of Alphard in Hydra


Alphard (Alpha Hydrae) Location in Hydra

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


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