Universe Guide


Delta Librae, 19 Librae, HD132742, HIP73473

Delta Librae is a blue eclipsing main sequence dwarf star that can be located in the constellation of Libra. Delta 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.

Delta Librae is the Bayer Classification for the star. HIP73473 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD132742.

Delta Librae has alternative name(s), del Lib.

Location of Delta 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 Delta Librae, the location is 15h 00m 58.39 and -08d31`08.2 .

Proper Motion of Delta 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 -4.76 ± 0.34 miliarcseconds/year towards the north and -63.46 ± 0.60 miliarcseconds/year east if we saw them in the horizon.

Delta Librae 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 42.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of Delta Librae

Delta Librae has a spectral type of B9.5V. This means the star is a blue main sequence dwarf star. The star is 7335.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23924.0812824000000000s. The star has a B-V Colour Index of 0 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 9,531 Kelvin.

Delta Librae Radius has been calculated as being 3.33 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,317,983.30.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.21. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Delta Librae Apparent and Absolute Magnitudes

Delta Librae has an apparent magnitude of 4.91 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 0.06 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.14. 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 Delta Librae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 10.72 which gave the calculated distance to Delta Librae as 304.26 light years away from Earth or 93.28 parsecs. It would take a spaceship travelling at the speed of light, 304.26 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 11.11 which put Delta Librae at a distance of 293.58 light years or 90.01 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 7,335.00 Parsecs or 23,924.08 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Delta Librae

The star is a eclipsing Beta Persei (Algol)/Semi-Detached System (subtype) variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. Delta Librae brightness ranges from a magnitude of 5.933 to a magnitude of 4.924 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 2.3 days (variability).

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.

Delta Librae Facts

Alternative Names

Flamsteed Name19 Librae
Flamsteed Short Name19 Lib
Short Namedel Lib
Bayer DesignationDelta Librae
Hipparcos Library I.D.73473
Bonner DurchmusterungBD-07 3938
Henry Draper Designation132742

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude0.06 / 0.14
Visual / Apparent Magnitude4.91
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)15h 00m 58.39
Declination (Dec.)-08d31`08.2
Galactic Latitude42.51 degrees
Galactic Longitude348.87 degrees
1997 Distance from Earth10.72 Parallax (milliarcseconds)
 304.26 Light Years
 93.28 Parsecs
2007 Revised Distance from Earth11.11 Parallax (milliarcseconds)
 293.58 Light Years
 90.01 Parsecs
Galacto-Centric Distance23,924.08 Light Years / 7,335.00 Parsecs
Proper Motion Dec.-4.76 ± 0.34 milliarcseconds/year
Proper Motion RA.-63.46 ± 0.60 milliarcseconds/year
B-V Index0.00
Radial Velocity-40.00 ± 4.20 km/s
Spectral TypeB9.5V
Colour(B) blue

Variable Star Details

Variable Star ClassEclipsing
Variable Star TypeBeta Persei (Algol)/Semi-Detached System (subtype)
Mean Variability Period in Days2.327
Variable Magnitude Range (Brighter - Dimmer)4.924 - 5.933

Estimated Facts

Luminosity (x the Sun)42.0000000
Calculated Effective Temperature9,531 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.

Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
132742-07 3938.0A-66.00000-9.00000A0White

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