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2 Hydrae, HD71297, HIP41375

2 Hydrae is a blue subgiant star that can be located in the constellation of Hydra. 2 Hydrae is the brightest star in Hydra based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

HIP41375 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD71297. The Id of the star in the Gould Star Catalogue is 23. 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.

Location of 2 Hydrae

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 2 Hydrae, the location is 08h 26m 27.23 and -03d59`14.3 .

Proper Motion of 2 Hydrae

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 -73.26 ± 0.26 miliarcseconds/year towards the north and -34.75 ± 0.38 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of 2 Hydrae

2 Hydrae has a spectral type of A5III-IV. This means the star is a blue subgiant star. The star is 7432.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24240.4597260800000000s. The star has a B-V Colour Index of 0.21 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 7,708 Kelvin.

2 Hydrae Radius has been calculated as being 2.11 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,470,567.89.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 1.99. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

2 Hydrae Apparent and Absolute Magnitudes

2 Hydrae has an apparent magnitude of 5.60 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 1.97 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.10. 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 2 Hydrae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 18.83 which gave the calculated distance to 2 Hydrae as 173.21 light years away from Earth or 53.11 parsecs. It would take a spaceship travelling at the speed of light, 173.21 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 19.99 which put 2 Hydrae at a distance of 163.16 light years or 50.03 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 7,432.00 Parsecs or 24,240.46 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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.

2 Hydrae Facts

Alternative Names

Traditional/Proper Name2 Hydrae
Flamsteed Name2 Hydrae
Flamsteed Short Name2 Hya
Hipparcos Library I.D.41375
Bonner DurchmusterungBD-03 2345
Gould I.D.23
Henry Draper Designation71297

Visual Facts

Star Typesubgiant star
Absolute Magnitude1.97 / 2.10
Visual / Apparent Magnitude5.60
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)08h 26m 27.23
Declination (Dec.)-03d59`14.3
Galactic Latitude19.02 degrees
Galactic Longitude227.96 degrees
1997 Distance from Earth18.83 Parallax (milliarcseconds)
 173.21 Light Years
 53.11 Parsecs
2007 Revised Distance from Earth19.99 Parallax (milliarcseconds)
 163.16 Light Years
 50.03 Parsecs
Galacto-Centric Distance24,240.46 Light Years / 7,432.00 Parsecs
Proper Motion Dec.-73.26 ± 0.26 milliarcseconds/year
Proper Motion RA.-34.75 ± 0.38 milliarcseconds/year
B-V Index0.21
Radial Velocity28.60 ± 0.30 km/s
Spectral TypeA5III-IV
Colour(A) blue

Estimated Facts

Calculated Effective Temperature7,708 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
71297-03 2345.0A5.40000-61.00000-64.00000A5White
B9.20000-61.00000-64.000001901

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