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Eta1 Hydri, HD11733, HIP8751

Eta1 Hydri is a blue main sequence dwarf star that can be located in the constellation of Hydrus. The description is based on the spectral class. The star can not be seen by the naked eye, you need a telescope to see it.

Eta1 Hydri's Alternative Names

Eta1 Hydri (Eta01 Hyi) is the Bayer Classification for the star. HIP8751 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD11733.

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

Location of Eta1 Hydri

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 Eta1 Hydri, the location is 01h 52m 34.74 and -67° 56` 40.2 .

Proper Motion of Eta1 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 -5.31 ± 0.29 miliarcseconds/year towards the north and 22.07 ± 0.33 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 us is 15.00000 km/s with an error of about 3.00 km/s .

Eta1 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 106.35 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of Eta1 Hydri

Eta1 Hydri has a spectral type of B9V. This means the star is a blue main sequence dwarf star. The star is 7,343.00 Parsecs from the Galactic Centre or terms of Light Years is 23,950.17 s. The star has a B-V Colour Index of -0.05 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 10,395 Kelvin.

Eta1 Hydri Radius has been calculated as being 2.92 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,031,136.63.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 2.77. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Eta1 Hydri Apparent and Absolute Magnitudes

Eta1 Hydri has an apparent magnitude of 6.77 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 -0.03 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.08. 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 Eta1 Hydri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.36 which gave the calculated distance to Eta1 Hydri as 748.08 light years away from Earth or 229.36 parsecs. It would take a spaceship travelling at the speed of light, 748.08 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 4.60 which put Eta1 Hydri at a distance of 709.05 light years or 217.39 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 7,343.00 Parsecs or 23,950.17 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.

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Eta1 Hydri Facts

Visual Facts


Primary / Proper / Traditional NameEta1 Hydri
Alternative NamesEta01 Hyi, HD 11733, HIP 8751
Spectral TypeB9V
Multiple Star SystemYes
Star Type main sequence Dwarf Star
Colour blue
GalaxyMilky Way
ConstellationHydrus
Absolute Magnitude-0.03 / 0.08
Visual / Apparent Magnitude6.77
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)01h 52m 34.74
Declination (Dec.)-67° 56` 40.2
Galactic Latitude-48.16 degrees
Galactic Longitude294.40 degrees
1997 Distance from Earth4.36 Parallax (milliarcseconds)
 748.08 Light Years
 229.36 Parsecs
2007 Distance from Earth4.60 Parallax (milliarcseconds)
 709.05 Light Years
 217.39 Parsecs
Galacto-Centric Distance23,950.17 Light Years / 7,343.00 Parsecs
Proper Motion Dec.-5.31 ± 0.29 milliarcseconds/year
Proper Motion RA.22.07 ± 0.33 milliarcseconds/year
B-V Index-0.05
Radial Velocity15.00 ± 3.00 km/s
Eccentricity0.12
Semi-Major Axis6562.00
Stellar Luminosity (Lsun)106.35

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Facts


Calculated Effective Temperature10,395 Kelvin

Sources and Links


SIMBAD SourceLink

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