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Brachium (Sigma Librae, 20 Librae) Star Facts

Brachium Facts

Brachium's Alternative Names

Sigma Librae (Sig Lib) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in the early nineteenth century. The brightest star in the constellation is normally given the Alpha designation although there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR5603. HIP73714 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD133216. The Gliese ID of the star is GL 574.1. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 20 Librae with it shortened to 20 Lib.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is CD-24 11834.

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

Location of Brachium

The location of the giant 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 object is compared to the celestial equator and is expressed in degrees. For Brachium, the location is 15h 04m 04.26 and -25° 16` 54.7 .

Radial Velocity and Proper Motion of Brachium

Proper Motion

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 -43.34 ± 0.14 miliarcseconds/year towards the north and -71.16 ± 0.25 miliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -3.90 km/s with an error of about 0.70 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties (Colour, Temperature) of Brachium

Brachium Colour and Temperature

Brachium has a spectral type of M3/M4III. This means the star is a red giant star. The star has a B-V Colour Index of 1.67 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 3,575 Kelvin.

Brachium Radius

Radius has been calculated as being 48.79 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 33,950,843.01.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 48.12. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Brachium Apparent and Absolute Magnitudes

Brachium has an apparent magnitude of 3.25 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 -1.51 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.48. 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 Brachium

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 11.17 which gave the calculated distance to Brachium as 292.00 light years away from Earth or 89.53 parsecs. It would take a spaceship travelling at the speed of light, 292.00 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 11.31 which put Brachium at a distance of 288.38 light years or 88.42 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.

Using the 2007 distance, the star is roughly 18,237,807.09 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun.

The star's Galacto-Centric Distance is 7,329.00 Parsecs or 23,904.51 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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Additional Brachium Facts and Figures

Visual Facts


Primary / Proper / Traditional NameBrachium
Alternative NamesSigma Librae, Sig Lib, HD 133216, HIP 73714, HR 5603, 20 Librae, 20 Lib, CD-24 11834, Gliese 574.1
Spectral TypeM3/M4III
Constellation's Main StarYes
Multiple Star SystemNo / Unknown
Star TypeGiant Star
ColourRed
GalaxyMilky Way
ConstellationLibra
Absolute Magnitude -1.51 / -1.48
Visual / Apparent Magnitude3.25
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)15h 04m 04.26
Declination (Dec.)-25° 16` 54.7
Galactic Latitude28.62 degrees
Galactic Longitude337.22 degrees
1997 Distance from Earth11.17 Parallax (milliarcseconds)
 292.00 Light Years
 89.53 Parsecs
2007 Distance from Earth11.31 Parallax (milliarcseconds)
 288.38 Light Years
 88.42 Parsecs
 18,237,807.09 Astronomical Units
Galacto-Centric Distance23,904.51 Light Years / 7,329.00 Parsecs
Proper Motion Dec.-43.34 ± 0.14 milliarcseconds/year
Proper Motion RA.-71.16 ± 0.25 milliarcseconds/year
B-V Index1.67
Radial Velocity-3.90 ± 0.70 km/s
Eccentricity0.16
Semi-Major Axis6248.00

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)48.12
Effective Temperature3,575 Kelvin

Sources and Links


SIMBAD SourceLink

Location of Brachium in Libra


Brachium Location in Libra

The map was generated using Night Vision, an awesome free application by Brian Simpson.

Libra Main Stars


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