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HD 157172 - HIP85017

HD 157172 is a white to yellow main sequence dwarf star that can be located in the constellation of Ophiuchus. HIP85017 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD157172. HD 157172 has at least 1 Extrasolar Planets believed to be in orbit around the star.

Location of HD 157172

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 HD 157172, the location is 17h 22m 34.56 and -19d36`57.0 .

Proper Motion of HD 157172

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 -138.50 ± 000.48 towards the north and 002.66 ± 000.89 east if we saw them in the horizon.

HD 157172 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 1.0000000 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 HD 157172

HD 157172 has a spectral type of G8V. This means the star is a white to yellow main sequence dwarf star. The star has a B-V Colour Index of 0.78 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,337 Kelvin.

HD 157172 has been calculated as 0.99 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 686,660.68.km.

HD 157172 Apparent and Absolute Magnitudes

HD 157172 has an apparent magnitude of 7.84 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 5.22 If you used the 2007 Parallax value, you would get an absolute magnitude of 5.32. 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 157172

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 29.87 which gave the calculated distance to HD 157172 as 109.19 light years away from Earth or 33.48 parsecs. It would take a spaceship travelling at the speed of light, 109.19 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 31.37 which put HD 157172 at a distance of 103.97 light years or 31.88 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.

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.

HD 157172 Facts

Alternative Names

Traditional NameHD 157172
Hipparcos Library I.D.85017
Bonner DurchmusterungBD-19 4615
Henry Draper Designation157172

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude5.22 / 5.32
Apparent Magnitude7.84
Right Ascension (R.A.)17h 22m 34.56
Declination (Dec.)-19d36`57.0
1997 Distance from Earth29.87 Parallax (milliarcseconds)
 109.19 Light Years
 33.48 Parsecs
2007 Revised Distance from Earth31.37 Parallax (milliarcseconds)
 103.97 Light Years
 31.88 Parsecs
Proper Motion Dec.-138.50 ± 0.48 milliarcseconds/year
Proper Motion RA.2.66 ± 0.89 milliarcseconds/year
B-V Index0.78
Spectral TypeG8V
Colour(G) White to Yellow

Companions (Multi-Star and Exoplanets) Facts

Exoplanet Count1

Estimated Facts

Radius (x the Sun)0.99
Luminosity (x the Sun)1.0000000
Calculated Effective Temperature5,337 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars


List of Extrasolar Planets orbiting HD 157172


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastron
Hd 157172 BConfirmed0.12104.8400.4620110.416

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