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HD 20781, HIP15526

HD 20781 is a orange to red main sequence dwarf star that can be located in the constellation of Fornax. 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. HD 20781 has at least 2 Extrasolar Planets believed to be in orbit around the star.

HD 20781's Alternative Names

HIP15526 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD20781.

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

Location of HD 20781

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 HD 20781, the location is 03h 20m 02.71 and -28° 47` 01.2 .

Proper Motion of HD 20781

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 -67.69 ± 0.77 miliarcseconds/year towards the north and 348.97 ± 1.08 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 40.14000 km/s with an error of about 0.36 km/s .

HD 20781 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 0.53 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 HD 20781

HD 20781 has a spectral type of K0V. This means the star is a orange to red main sequence dwarf star. The star is 7,414.00 Parsecs from the Galactic Centre or terms of Light Years is 24,181.75 s. The star has a B-V Colour Index of 0.82 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,236 Kelvin.

HD 20781 Radius has been calculated as being 0.82 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 569,288.61.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 0.81. 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 -0.08 with an error value of 0.03 Fe/H with the Sun has a value of 1 to put it into context.

HD 20781 Apparent and Absolute Magnitudes

HD 20781 has an apparent magnitude of 8.48 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 5.71 If you used the 2007 Parallax value, you would get an absolute magnitude of 5.74. 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 HD 20781

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 27.86 which gave the calculated distance to HD 20781 as 117.07 light years away from Earth or 35.89 parsecs. It would take a spaceship travelling at the speed of light, 117.07 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 28.27 which put HD 20781 at a distance of 115.37 light years or 35.37 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 7,414.00 Parsecs or 24,181.75 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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HD 20781 Facts

Visual Facts


Primary / Proper / Traditional NameHD 20781
Alternative NamesHD 20781, HIP 15526
Spectral TypeK0V
Multiple Star SystemYes
Star Type main sequence Dwarf Star
Colour orange to red
GalaxyMilky Way
ConstellationFornax
Absolute Magnitude5.71 / 5.74
Visual / Apparent Magnitude8.48
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)03h 20m 02.71
Declination (Dec.)-28° 47` 01.2
Galactic Latitude-57.27 degrees
Galactic Longitude224.67 degrees
1997 Distance from Earth27.86 Parallax (milliarcseconds)
 117.07 Light Years
 35.89 Parsecs
2007 Distance from Earth28.27 Parallax (milliarcseconds)
 115.37 Light Years
 35.37 Parsecs
Galacto-Centric Distance24,181.75 Light Years / 7,414.00 Parsecs
Proper Motion Dec.-67.69 ± 0.77 milliarcseconds/year
Proper Motion RA.348.97 ± 1.08 milliarcseconds/year
B-V Index0.82
Radial Velocity40.14 ± 0.36 km/s
Iron Abundance-0.08 ± 0.03 Fe/H
Eccentricity0.40
Semi-Major Axis4913.00
Stellar Luminosity (Lsun)0.53

Companions (Multi-Star and Exoplanets) Facts


Exoplanet Count2

Estimated Facts


Calculated Effective Temperature5,236 Kelvin

Sources and Links


SIMBAD SourceLink

List of Extrasolar Planets orbiting HD 20781


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastronInclination
HD 20781 bConfirmed0.003529.1500.1120110.1692011.000
HD 20781 cConfirmed0.003885.1310.2820110.34562011.000

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