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Gamma Hydri, HD24512, HIP17678, HR1208

Gamma Hydri is a red pulsating giant star that can be located in the constellation of Hydrus. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Gamma Hydri's Alternative Names

Gamma Hydri (Gam Hyi) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR1208. HIP17678 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD24512.

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

Location of Gamma Hydri

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 Gamma Hydri, the location is 03h 47m 14.23 and -74° 14` 21.3 .

Proper Motion of Gamma Hydri

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 114.74 ± 0.11 miliarcseconds/year towards the north and 50.85 ± 0.11 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 15.80000 km/s with an error of about 0.60 km/s .

Gamma Hydri 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 718.42 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 Gamma Hydri

Gamma Hydri has a spectral type of M2III. This means the star is a red giant star. The star is 7,383.00 Parsecs from the Galactic Centre or terms of Light Years is 24,080.64 s. The star has a B-V Colour Index of 1.59 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 3,804 Kelvin.

Gamma Hydri Radius has been calculated as being 31.51 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 21,923,756.12.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 31.51. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Gamma Hydri Apparent and Absolute Magnitudes

Gamma Hydri has an apparent magnitude of 3.26 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 -0.83 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.83. 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 Gamma Hydri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 15.23 which gave the calculated distance to Gamma Hydri as 214.16 light years away from Earth or 65.66 parsecs. It would take a spaceship travelling at the speed of light, 214.16 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 15.24 which put Gamma Hydri at a distance of 214.02 light years or 65.62 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 7,383.00 Parsecs or 24,080.64 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 Gamma Hydri

The star is a pulsating Semi-Regular Star which are giants or supergiants of intermediate and late spectral 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. Gamma Hydri brightness ranges from a magnitude of 3.375 to a magnitude of 3.320 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.0 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 Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

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Gamma Hydri Facts

Visual Facts


 Gamma Hydri
Alternative NamesGam Hyi, HD 24512, HIP 17678, HR 1208
Spectral TypeM2III
Multiple Star SystemNo / Unknown
Star TypeGiant Star
Colour red
GalaxyMilky Way
ConstellationHydrus
Absolute Magnitude-0.83 / -0.83
Visual / Apparent Magnitude3.26
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 47m 14.23
Declination (Dec.)-74° 14` 21.3
Galactic Latitude-37.80 degrees
Galactic Longitude289.13 degrees
1997 Distance from Earth15.23 Parallax (milliarcseconds)
 214.16 Light Years
 65.66 Parsecs
2007 Distance from Earth15.24 Parallax (milliarcseconds)
 214.02 Light Years
 65.62 Parsecs
Galacto-Centric Distance24,080.64 Light Years / 7,383.00 Parsecs
Proper Motion Dec.114.74 ± 0.11 milliarcseconds/year
Proper Motion RA.50.85 ± 0.11 milliarcseconds/year
B-V Index1.59
Radial Velocity15.80 ± 0.60 km/s
Eccentricity0.09
Semi-Major Axis7156.00
Stellar Luminosity (Lsun)718.42

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeSemi-Regular Star which are giants or supergiants of intermediate and late spectral
Mean Variability Period in Days0.044
Variable Magnitude Range (Brighter - Dimmer)3.320 - 3.375

Estimated Facts


Calculated Effective Temperature3,804 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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