Universe Guide


15 Pegasi, HD207978, HIP107975

15 Pegasi is a blue to white subgiant star that can be located in the constellation of Pegasus. 15 Pegasi is the brightest star in Pegasus 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 3.30 Billion of Years but could be as young as 3.00 to 4.50 according to Hipparcos.

HIP107975 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD207978.

Location of 15 Pegasi

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 15 Pegasi, the location is 21h 52m 29.96 and +28d47`37.3 .

Proper Motion of 15 Pegasi

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 -62.37 ± 0.26 miliarcseconds/year towards the north and -58.81 ± 0.32 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Age, Radius) of 15 Pegasi

15 Pegasi has a spectral type of F6IVwvar. This means the star is a blue to white subgiant star. The star is 7396.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24123.0409222400000000s. The star has a B-V Colour Index of 0.42 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,635 Kelvin.

15 Pegasi Radius has been calculated as being 1.54 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,070,714.00.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 1.52. 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 -0.53 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 3.30 Billion years old but could be between 3.00 and 4.50 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

15 Pegasi Apparent and Absolute Magnitudes

15 Pegasi has an apparent magnitude of 5.52 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 3.31 If you used the 2007 Parallax value, you would get an absolute magnitude of 3.33. 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 15 Pegasi

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 36.15 which gave the calculated distance to 15 Pegasi as 90.22 light years away from Earth or 27.66 parsecs. It would take a spaceship travelling at the speed of light, 90.22 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 36.43 which put 15 Pegasi at a distance of 89.53 light years or 27.45 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 7,396.00 Parsecs or 24,123.04 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.

15 Pegasi Facts

Alternative Names

Traditional/Proper Name15 Pegasi
Flamsteed Name15 Pegasi
Flamsteed Short Name15 Peg
Hipparcos Library I.D.107975
Bonner DurchmusterungBD+28 4215
Henry Draper Designation207978

Visual Facts

Star Typesubgiant star
Age3.30 Billion Years Old
Age Range3.00 - 4.50 Billion Years Old
Absolute Magnitude3.31 / 3.33
Visual / Apparent Magnitude5.52
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)21h 52m 29.96
Declination (Dec.)+28d47`37.3
Galactic Latitude-19.54 degrees
Galactic Longitude82.05 degrees
1997 Distance from Earth36.15 Parallax (milliarcseconds)
 90.22 Light Years
 27.66 Parsecs
2007 Revised Distance from Earth36.43 Parallax (milliarcseconds)
 89.53 Light Years
 27.45 Parsecs
Galacto-Centric Distance24,123.04 Light Years / 7,396.00 Parsecs
Proper Motion Dec.-62.37 ± 0.26 milliarcseconds/year
Proper Motion RA.-58.81 ± 0.32 milliarcseconds/year
B-V Index0.42
Radial Velocity18.93 ± 0.09 km/s
Iron Abundance-0.53 ± 0.01 Fe/H
Spectral TypeF6IVwvar
Colour(F) blue to white

Estimated Facts

Calculated Effective Temperature6,635 Kelvin

Sources and Links

SIMBAD SourceLink

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