Universe Guide


U Hydrae, HD92055, HIP52009

U Hydrae is a pulsating star that can be located in the constellation of Hydra. U 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.

HIP52009 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD92055. The Id of the star in the Gould Star Catalogue is 240. 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.

U Hydrae has alternative name(s), U Hya.

Location of U 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 U Hydrae, the location is 10h 37m 33.25 and -13d23`04.0 .

Proper Motion of U 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 -37.72 ± 0.16 miliarcseconds/year towards the north and 42.59 ± 0.23 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Temperature, Radius) of U Hydrae

U Hydrae has a spectral type of C. This means the star is a star. The star is 7431.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24237.1980926400000000s. The star has a B-V Colour Index of 2.8 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 0 Kelvin. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.02 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

U Hydrae Apparent and Absolute Magnitudes

U Hydrae has an apparent magnitude of 4.89 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 -1.16 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.70. 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 U Hydrae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 6.18 which gave the calculated distance to U Hydrae as 527.77 light years away from Earth or 161.81 parsecs. It would take a spaceship travelling at the speed of light, 527.77 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 4.80 which put U Hydrae at a distance of 679.51 light years or 208.33 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.

The star's Galacto-Centric Distance is 7,431.00 Parsecs or 24,237.20 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 U Hydrae

The star is a pulsating Semiregular late- (M, C, S or Me, Ce, Se) giants with poorly defined periodicity 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. U Hydrae brightness ranges from a magnitude of 5.019 to a magnitude of 4.795 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 114.8 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.

U Hydrae Facts

Alternative Names

Traditional/Proper NameU Hydrae
Short NameU Hya
Hipparcos Library I.D.52009
Bonner DurchmusterungBD-12 3218
Gould I.D.240
Henry Draper Designation92055

Visual Facts

Star Type star
Absolute Magnitude-1.16 / -1.70
Visual / Apparent Magnitude4.89
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)10h 37m 33.25
Declination (Dec.)-13d23`04.0
Galactic Latitude38.07 degrees
Galactic Longitude259.97 degrees
1997 Distance from Earth6.18 Parallax (milliarcseconds)
 527.77 Light Years
 161.81 Parsecs
2007 Revised Distance from Earth4.80 Parallax (milliarcseconds)
 679.51 Light Years
 208.33 Parsecs
Galacto-Centric Distance24,237.20 Light Years / 7,431.00 Parsecs
Proper Motion Dec.-37.72 ± 0.16 milliarcseconds/year
Proper Motion RA.42.59 ± 0.23 milliarcseconds/year
B-V Index2.80
Radial Velocity-25.80 ± 1.70 km/s
Iron Abundance0.02 ± 9.99 Fe/H
Spectral TypeC

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSemiregular late- (M, C, S or Me, Ce, Se) giants with poorly defined periodicity
Mean Variability Period in Days114.800
Variable Magnitude Range (Brighter - Dimmer)4.795 - 5.019

Estimated Facts

Sources and Links

SIMBAD SourceLink

Related Stars

Location of U Hydrae in Hydra

U Hydrae Location in Hydra

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

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