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VX Hydrae, HIP47904

VX Hydrae is a blue to white pulsating supergiant star that can be located in the constellation of Hydra. The description is based on the spectral class. VX Hydrae is not part of the constellation but is within the borders of the constellation.

The star can not be seen by the naked eye, you need a telescope to see it.

VX Hydrae's Alternative Names

HIP47904 is the reference name for the star in the Hipparcos Star Catalogue.

VX Hydrae has alternative name(s) :- , VX Hya.

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

Location of VX Hydrae

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 VX Hydrae, the location is 09h 45m 46.85 and -12° 00` 14.5 .

Radial Velocity and Proper Motion of VX 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 12.73 ± 1.61 miliarcseconds/year towards the north and -8.88 ± 2.67 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 the Sun is -15.00 km/s with an error of about 7.40 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties (Colour, Temperature) of VX Hydrae

VX Hydrae has a spectral type of F2-F8Ib. This means the star is a blue to white supergiant star. The star has a B-V Colour Index of 0.66 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,739 Kelvin.

VX Hydrae Radius has been calculated as being 1.61 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,121,186.04.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 1.06. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

VX Hydrae Apparent and Absolute Magnitudes

VX Hydrae has an apparent magnitude of 10.68 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 3.84 If you used the 2007 Parallax value, you would get an absolute magnitude of 4.75. 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 VX Hydrae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.28 which gave the calculated distance to VX Hydrae as 762.06 light years away from Earth or 233.64 parsecs. It would take a spaceship travelling at the speed of light, 762.06 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 6.51 which put VX Hydrae at a distance of 501.02 light years or 153.61 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.

Using the 2007 distance, the star is roughly 31,684,116.11 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun.

Variable Type of VX Hydrae

The star is a pulsating Delta Scuti 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. VX Hydrae brightness ranges from a magnitude of 10.955 to a magnitude of 10.511 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.2 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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VX Hydrae Facts

Visual Facts


Primary / Proper / Traditional NameVX Hydrae
Alternative NamesHIP 47904, VX Hya
Spectral TypeF2-F8Ib
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star Type very luminous Supergiant Star
Colour blue to white
GalaxyMilky Way
ConstellationHydra
Absolute Magnitude 3.84 / 4.75
Visual / Apparent Magnitude10.68
Naked Eye VisibleRequires a 4.5 - 6 Inch Telescope - Magnitudes
Right Ascension (R.A.)09h 45m 46.85
Declination (Dec.)-12° 00` 14.5
Galactic Latitude30.35 degrees
Galactic Longitude247.74 degrees
1997 Distance from Earth4.28 Parallax (milliarcseconds)
 762.06 Light Years
 233.64 Parsecs
2007 Distance from Earth6.51 Parallax (milliarcseconds)
 501.02 Light Years
 153.61 Parsecs
 31,684,116.11 Astronomical Units
Proper Motion Dec.12.73 ± 1.61 milliarcseconds/year
Proper Motion RA.-8.88 ± 2.67 milliarcseconds/year
B-V Index0.66
Radial Velocity-15.00 ± 7.40 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeDelta Scuti
Mean Variability Period in Days0.217
Variable Magnitude Range (Brighter - Dimmer)10.511 - 10.955

Estimated Facts


Calculated Effective Temperature5,739 Kelvin

Sources and Links


SIMBAD SourceLink

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