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Eta Hydri, HD11977, HIP8928

Eta Hydri is a white to yellow giant star that can be located in the constellation of Hydrus. Eta Hydri is the brightest star in Hydrus 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. It is calculated at being 1.250 Billion Years old. This information comes from ExoPlanet.

Eta Hydri is the Bayer Classification for the star. HIP8928 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD11977. Eta Hydri has at least 1 Extrasolar Planets believed to be in orbit around the star.

Location of Eta Hydri

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 Eta Hydri, the location is 01h 54m 56.01 and -67d38`50.9 .

Proper Motion of Eta Hydri

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 72.94 ± 0.14 miliarcseconds/year towards the north and 76.22 ± 0.16 miliarcseconds/year east if we saw them in the horizon.

Eta Hydri Luminosity

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 127.0000000 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.

Physical Properties (Colour, Temperature, Age, Mass, Radius) of Eta Hydri

Eta Hydri has a spectral type of G5III. This means the star is a white to yellow giant star. The star is 7382.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24077.3780540800000000s. The star has a B-V Colour Index of 0.93 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,989 Kelvin.

Eta Hydri Radius has been calculated as being 9.61 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 6,688,908.06.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 9.70. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's solar mass is 1.91 times that of the Sun's. The Sun's Mass is 1,989,100,000,000,000,000,000 billion kg. which to calculate using this website is too large. To give idea of size, the Sun is 99.86% the mass of the solar system.

The star's metallicity is -0.210000, this value is the fractional amount of the star that is not Hydrogen (X) or Helium (Y). An older star would have a high metallicity whereas a new star would have a lower one.

The star is believed to be about 1.25 Billion years old. To put in context, the Sun is believed to be about five billion years old and the Universe is about 13.8 billion years old.

Eta Hydri Apparent and Absolute Magnitudes

Eta Hydri has an apparent magnitude of 4.68 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 0.57 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.55. 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 Eta Hydri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 15.04 which gave the calculated distance to Eta Hydri as 216.86 light years away from Earth or 66.49 parsecs. It would take a spaceship travelling at the speed of light, 216.86 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 14.91 which put Eta Hydri at a distance of 218.75 light years or 67.07 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 7,382.00 Parsecs or 24,077.38 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.

Eta Hydri Facts

Alternative Names

Bayer DesignationEta Hydri
Hipparcos Library I.D.8928
Henry Draper Designation11977

Visual Facts

Star Typegiant star
Age1.25 Billion Years Old
Absolute Magnitude0.57 / 0.55
Visual / Apparent Magnitude4.68
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)01h 54m 56.01
Declination (Dec.)-67d38`50.9
Galactic Latitude-48.36 degrees
Galactic Longitude293.93 degrees
1997 Distance from Earth15.04 Parallax (milliarcseconds)
 216.86 Light Years
 66.49 Parsecs
2007 Revised Distance from Earth14.91 Parallax (milliarcseconds)
 218.75 Light Years
 67.07 Parsecs
Galacto-Centric Distance24,077.38 Light Years / 7,382.00 Parsecs
Proper Motion Dec.72.94 ± 0.14 milliarcseconds/year
Proper Motion RA.76.22 ± 0.16 milliarcseconds/year
B-V Index0.93
Radial Velocity-16.20 ± 2.80 km/s
Iron Abundance-0.12 ± 0.03 Fe/H
Spectral TypeG5III
Colour(G) White to Yellow

Companions (Multi-Star and Exoplanets) Facts

Exoplanet Count1

Estimated Facts

Luminosity (x the Sun)127.0000000
Calculated Effective Temperature4,989 Kelvin
Mass Compared to the Sun1.91
Metallicity-0.21000

Sources and Links

SIMBAD SourceLink

Related Stars


List of Extrasolar Planets orbiting Eta Hydri


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastron
Hd 11977 BConfirmed6.29711.0000.420051.89352.000

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