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Unukalhai (Alpha Serpentis) - HD140573 - HIP77070 - HR5854

Unukalhai (Alpha Serpentis) is a orange to red giant star that can be located in the constellation of Serpens. Alpha Serpentis is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR5854. HIP77070 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD140573. The Id of the star in the Gould Star Catalogue is 21 Cap. 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. Unukalhai has alternative name(s), 24 Serpentis , 24 Ser. In Arabic, it is known as 'Unuq al-Hayyah.

Location of Unukalhai

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 Unukalhai, the location is 15h 44m 16.00 and +06d25`31.9 .

Proper Motion of Unukalhai

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 044.81 ± 000.12 towards the north and 133.84 ± 000.19 east if we saw them in the horizon.

Unukalhai 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 70.0000000 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 Unukalhai

Unukalhai has a spectral type of K2III. This means the star is a orange to red giant star. The star has a B-V Colour Index of 1.16 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,558 Kelvin.

Unukalhai has been calculated as 10.03 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 6,979,601.82.km.

Unukalhai Apparent and Absolute Magnitudes

Unukalhai has an apparent magnitude of 2.63 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 0.87 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.85. 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 Unukalhai

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 44.54 which gave the calculated distance to Unukalhai as 73.23 light years away from Earth or 22.45 parsecs. It would take a spaceship travelling at the speed of light, 73.23 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 44.10 which put Unukalhai at a distance of 73.96 light years or 22.68 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.

Unukalhai Facts

Alternative Names

Traditional NameUnukalhai
Short Name24 Ser
Arabic Name'Unuq al-Hayyah
English MeaningNeck of the snake
Bayer DesignationAlpha Serpentis
Alternative Name(s)24 Serpentis
Hipparcos Library I.D.77070
Yale Bright Star Catalogue (HR) Id5854
Bonner DurchmusterungBD+06 3088
Gould I.D.21 Cap
Henry Draper Designation140573

Visual Facts

Star Typegiant star
Absolute Magnitude0.87 / 0.85
Apparent Magnitude2.63
Right Ascension (R.A.)15h 44m 16.00
Declination (Dec.)+06d25`31.9
1997 Distance from Earth44.54 Parallax (milliarcseconds)
 73.23 Light Years
 22.45 Parsecs
2007 Revised Distance from Earth44.10 Parallax (milliarcseconds)
 73.96 Light Years
 22.68 Parsecs
Proper Motion Dec.44.81 ± 0.12 milliarcseconds/year
Proper Motion RA.133.84 ± 0.19 milliarcseconds/year
B-V Index1.16
Spectral TypeK2III
Colour(K) Orange to Red

Estimated Facts

Radius (x the Sun)10.03
Luminosity (x the Sun)70.0000000
Calculated Effective Temperature4,558 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
140573+06 3088.0A2.80000136.0000044.00000K0Orange
B11.800001911
C1960

Location of Unukalhai in Serpens


Unukalhai (Alpha Serpentis) Location in Serpens

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


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