Universe Guide


Epsilon Librae, 31 Librae, HD137052, HIP75379

Epsilon Librae is a blue to white subgiant star that can be located in the constellation of Libra. Epsilon Librae is the brightest star in Libra 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 1.90 Billion of Years but could be as young as 1.80 to 2.00 according to Hipparcos.

Epsilon Librae is the Bayer Classification for the star. HIP75379 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD137052.

Location of Epsilon Librae

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 Epsilon Librae, the location is 15h 24m 11.93 and -10d19`18.8 .

Proper Motion of Epsilon Librae

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 -154.24 ± 0.44 miliarcseconds/year towards the north and -66.52 ± 0.72 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Age, Radius) of Epsilon Librae

Epsilon Librae has a spectral type of F5IV. This means the star is a blue to white subgiant star. The star is 7375.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24054.5466200000000000s. The star has a B-V Colour Index of 0.45 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,500 Kelvin.

Epsilon Librae Radius has been calculated as being 2.47 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,720,037.24.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.38. 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 -0.05 with an error value of 0.01 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 1.90 Billion years old but could be between 1.80 and 2.00 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Epsilon Librae Apparent and Absolute Magnitudes

Epsilon Librae has an apparent magnitude of 4.92 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 2.37 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.45. 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 Epsilon Librae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 30.90 which gave the calculated distance to Epsilon Librae as 105.55 light years away from Earth or 32.36 parsecs. It would take a spaceship travelling at the speed of light, 105.55 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 32.02 which put Epsilon Librae at a distance of 101.86 light years or 31.23 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 7,375.00 Parsecs or 24,054.55 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.

Epsilon Librae Facts

Alternative Names

Flamsteed Name31 Librae
Flamsteed Short Name31 Lib
Bayer DesignationEpsilon Librae
Hipparcos Library I.D.75379
Bonner DurchmusterungBD-09 4138
Henry Draper Designation137052

Visual Facts

Star Typesubgiant star
Age1.90 Billion Years Old
Age Range1.80 - 2.00 Billion Years Old
Absolute Magnitude2.37 / 2.45
Visual / Apparent Magnitude4.92
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)15h 24m 11.93
Declination (Dec.)-10d19`18.8
Galactic Latitude37.34 degrees
Galactic Longitude352.84 degrees
1997 Distance from Earth30.90 Parallax (milliarcseconds)
 105.55 Light Years
 32.36 Parsecs
2007 Revised Distance from Earth32.02 Parallax (milliarcseconds)
 101.86 Light Years
 31.23 Parsecs
Galacto-Centric Distance24,054.55 Light Years / 7,375.00 Parsecs
Proper Motion Dec.-154.24 ± 0.44 milliarcseconds/year
Proper Motion RA.-66.52 ± 0.72 milliarcseconds/year
B-V Index0.45
Radial Velocity-9.80 ± 0.70 km/s
Iron Abundance-0.05 ± 0.01 Fe/H
Semi-Major Axis8.42
Orbital Period (Days)226.95
Argument Of Periastron339.52
Spectral TypeF5IV
Colour(F) blue to white

Estimated Facts

Calculated Effective Temperature6,500 Kelvin

Sources and Links

SIMBAD SourceLink

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