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Beta Hydri, HD2151, HIP2021, HR98

Beta Hydri (Beta Hydri) Location in Hydrus

Beta Hydri is a white to yellow subgiant star that can be located in the constellation of Hydrus. The description is based on the spectral class. Beta Hydri is the 1st 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. The star has an estimated age of 5.30 Billion of Years but could be as young as 5.00 to 5.80 according to Hipparcos.

Beta Hydri's Alternative Names

Beta Hydri (Bet Hyi) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR98. HIP2021 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD2151. The Gliese ID of the star is GL 19. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

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

Location of Beta 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 Beta Hydri, the location is 00h 25m 39.20 and -77° 15` 18.1 .

Proper Motion of Beta 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 324.09 ± 0.10 miliarcseconds/year towards the north and 2,219.54 ± 0.11 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 22.10000 km/s with an error of about 0.60 km/s .

Beta 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 3.77 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, Age) of Beta Hydri

Beta Hydri has a spectral type of G2IV. This means the star is a white to yellow subgiant star. The star is 7,397.00 Parsecs from the Galactic Centre or terms of Light Years is 24,126.30 s. The star has a B-V Colour Index of 0.6 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,895 Kelvin.

Beta Hydri Radius has been calculated as being 1.83 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,271,704.89.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 1.82. 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 -0.12 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 5.30 Billion years old but could be between 5.00 and 5.80 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Beta Hydri Apparent and Absolute Magnitudes

Beta Hydri has an apparent magnitude of 2.82 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 3.45 If you used the 2007 Parallax value, you would get an absolute magnitude of 3.46. 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 Beta Hydri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 133.78 which gave the calculated distance to Beta Hydri as 24.38 light years away from Earth or 7.47 parsecs. It would take a spaceship travelling at the speed of light, 24.38 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 134.07 which put Beta Hydri at a distance of 24.33 light years or 7.46 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 7,397.00 Parsecs or 24,126.30 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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Beta Hydri Facts

Visual Facts


Primary / Proper / Traditional NameBeta Hydri
Alternative NamesBet Hyi, HD 2151, HIP 2021, HR 98, Gliese 19
Spectral TypeG2IV
Multiple Star SystemNo / Unknown
Star TypeSubgiant Star
Colour white to yellow
GalaxyMilky Way
ConstellationHydrus
Age5.30 Billion Years Old
Age Range5.00 - 5.80 Billion Years Old
Absolute Magnitude3.45 / 3.46
Visual / Apparent Magnitude2.82
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)00h 25m 39.20
Declination (Dec.)-77° 15` 18.1
Galactic Latitude-39.78 degrees
Galactic Longitude304.78 degrees
1997 Distance from Earth133.78 Parallax (milliarcseconds)
 24.38 Light Years
 7.47 Parsecs
2007 Distance from Earth134.07 Parallax (milliarcseconds)
 24.33 Light Years
 7.46 Parsecs
Galacto-Centric Distance24,126.30 Light Years / 7,397.00 Parsecs
Proper Motion Dec.324.09 ± 0.10 milliarcseconds/year
Proper Motion RA.2219.54 ± 0.11 milliarcseconds/year
B-V Index0.60
Radial Velocity22.10 ± 0.60 km/s
Iron Abundance-0.12 ± 9.99 Fe/H
Eccentricity0.33
Semi-Major Axis5751.00
Stellar Luminosity (Lsun)3.77

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Facts


Calculated Effective Temperature5,895 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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