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R Hydrae - HD117287 - HIP65835

R Hydrae is a red pulsating star that can be located in the constellation of Hydra. HIP65835 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD117287. The Id of the star in the Gould Star Catalogue is 347. 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. R Hydrae has alternative name(s), R_Hya.

Location of R 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 R Hydrae, the location is 13h 29m 42.82 and -23d16`52.9 .

Proper Motion of R 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 012.86 ± 000.46 towards the north and -057.68 ± 000.69 east if we saw them in the horizon.

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

R Hydrae has a spectral type of M6/M7e. This means the star is a red star. The star has a B-V Colour Index of 1.31 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,369 Kelvin.

R Hydrae has been calculated as 52.74 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 36,698,539.05.km.

R Hydrae Apparent and Absolute Magnitudes

R Hydrae has an apparent magnitude of 6.40 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 -2.55 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.93. 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 R Hydrae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 1.62 which gave the calculated distance to R Hydrae as 2013.35 light years away from Earth or 617.28 parsecs. In 2007, Hipparcos data was revised with a new parallax of 8.05 which put R Hydrae at a distance of 405.17 light years or 124.22 parsecs.

It would take a spaceship travelling at the speed of light, 2013.35 years using the 1997 distance to get there. We don't have the technology or spaceship that can carry people over that distance yet.

Variable Type of R Hydrae

The star is a pulsating Omicron Ceti 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. R Hydrae brightness ranges from a magnitude of 7.000 to a magnitude of 4.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 384.0 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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

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R Hydrae Facts

Alternative Names

Traditional NameR Hydrae
Short NameR Hya
Hipparcos Library I.D.65835
Bonner DurchmusterungBD-22 3601
Gould I.D.347
Henry Draper Designation117287

Visual Facts

Star Type star
Absolute Magnitude-2.55 / 0.93
Apparent Magnitude6.40
Right Ascension (R.A.)13h 29m 42.82
Declination (Dec.)-23d16`52.9
1997 Distance from Earth1.62 Parallax (milliarcseconds)
 2013.35 Light Years
 617.28 Parsecs
2007 Distance from Earth8.05 Parallax (milliarcseconds)
 405.17 Light Years
 124.22 Parsecs
Proper Motion Dec.12.86 ± 0.46 milliarcseconds/year
Proper Motion RA.-57.68 ± 0.69 milliarcseconds/year
B-V Index1.31
Spectral TypeM6/M7e
Colour(M) Red

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeOmicron Ceti
Mean Variability Period in Days384.000
Variable Magnitude Range (Brighter - Dimmer)4.000 - 7.000

Estimated Facts

Radius (x the Sun)52.74
Calculated Effective Temperature4,369 Kelvin

Sources and Links

SIMBAD SourceLink

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
117287-22 3601.0A-56.0000011.00000M8Red
B12.00000-56.0000011.000001891

Location of R Hydrae in Hydra


R Hydrae Location in Hydra

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



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