Tau 1 Hydrae is a blue to white main sequence dwarf star that can be located in the constellation of Hydra. Tau 1 Hydrae is the Bayer Classification for the star. HIP46509 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD81997. The Id of the star in the Gould Star Catalogue is 145. 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. Tau 1 Hydrae has alternative name(s), 31 Hydrae , 31 Hya.
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 Tau 1 Hydrae, the location is 09h 29m 08.84 and -02d46`08.2 .
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 -002.67 ± 001.25 towards the north and 099.01 ± 002.14 east if we saw them in the horizon.
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 2.0000000 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.
Tau 1 Hydrae has a spectral type of F6V. This means the star is a blue to white main sequence dwarf star. The star has a B-V Colour Index of 0.41 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,681 Kelvin.
Tau 1 Hydrae has been calculated as 1.44 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 999,243.23.km.
Tau 1 Hydrae has an apparent magnitude of 4.59 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 3.43 If you used the 2007 Parallax value, you would get an absolute magnitude of 3.40. 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.
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 58.48 which gave the calculated distance to Tau 1 Hydrae as 55.77 light years away from Earth or 17.10 parsecs. It would take a spaceship travelling at the speed of light, 55.77 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 57.69 which put Tau 1 Hydrae at a distance of 56.54 light years or 17.33 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.
|Short Name||31 Hya|
|Bayer Designation||Tau 1 Hydrae|
|Alternative Name(s)||31 Hydrae|
|Hipparcos Library I.D.||46509|
|Bonner Durchmusterung||BD-02 2901|
|Henry Draper Designation||81997|
|Star Type||main sequence dwarf star|
|Absolute Magnitude||3.43 / 3.40|
|Right Ascension (R.A.)||09h 29m 08.84|
|1997 Distance from Earth||58.48 Parallax (milliarcseconds)|
|55.77 Light Years|
|2007 Revised Distance from Earth||57.69 Parallax (milliarcseconds)|
|56.54 Light Years|
|Proper Motion Dec.||-2.67 ± 1.25 milliarcseconds/year|
|Proper Motion RA.||99.01 ± 2.14 milliarcseconds/year|
|Colour||(F) blue to white|
|Radius (x the Sun)||1.44|
|Luminosity (x the Sun)||2.0000000|
|Calculated Effective Temperature||6,681 Kelvin|
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. Id||B.D. Id||Star Code||Magnitude||R.A.||Dec.||Spectrum||Colour||Year|