Universe Guide

138 G. Oph - HD157856 - HIP85307

138 G. Oph is a blue to white main sequence dwarf star that can be located in the constellation of Ophiuchus. HIP85307 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD157856. The Id of the star in the Gould Star Catalogue is 138. Stars in the southern hemisphere are more likely to have a Gould Id than the northern hemisphere. For example, there are no Gould classified stars in Ursa Major.

Location of 138 G. Oph

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 from celestial equator. The Declination is how up or down compared to the celestial equator and is expressed in degrees. For 138 G. Oph, the location is 17h 25m 57.84 and -01 d 39`06.9 .

Proper Motion of 138 G. Oph

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 052.00 ± 000.00 towards the north and 061.00 ± 000.00 east if we saw them in the horizon.

138 G. Oph 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 3.0000000 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 138 G. Oph

138 G. Oph has a spectral type of F3V. This means the star is a blue to white coloured main sequence dwarf star. 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.

138 G. Oph has been calculated as 2.37 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,650,201.46.km.

138 G. Oph Apparent and Absolute Magnitudes

138 G. Oph has an apparent magnitude of 6.44 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 2.46 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.46. 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 138 G. Oph

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 16.00 which gave the calculated distance to 138 G. Oph as 203.85 light years away from us or 62.5 parsecs. In 2007, Hipparcos data was revised with a new parallax of 16.00 which put 138 G. Oph at a distance of 203.85 light years or 62.5 parsecs.

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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

138 G. Oph Facts


Traditional Name138 G. Oph
Hipparcos Library I.D.85307
Gould I.D.138
Henry Draper Designation157856
Celestial TypeStar
Absolute Magnitude2.46 / 2.46
Apparent Magnitude6.44
Right Ascension (R.A.)17h 25m 57.84
Declination (Dec.)-01 d 39`06.9
1997 Distance16.00 Parallax (milliarcseconds)
 203.85 Light Years
 62.5 Parsecs
2007 Distance16.00 Parallax (milliarcseconds)
 203.85 Light Years
 62.5 Parsecs
Proper Motion Dec.52.00 ± 0.00 milliarcseconds/year
Proper Motion RA.61.00 ± 0.00 milliarcseconds/year
B-V Index0.45
Spectral TypeF3V
Colour(F) blue to white
Star Typemain sequence dwarf star
Radius (x the Sun)2.37
Luminosity (x the Sun)3.0000000
Calculated Effective Temperature6,500 Kelvin


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