Universe Guide


Tau7 Serpentis, 22 Serpentis, HD140232, HIP76878

Tau7 Serpentis is a blue star that can be located in the constellation of Serpens. Tau7 Serpentis is the brightest star in Serpens 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.

Tau7 Serpentis is the Bayer Classification for the star. HIP76878 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD140232.

Location of Tau7 Serpentis

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 Tau7 Serpentis, the location is 15h 41m 54.76 and +18d27`50.0 .

Proper Motion of Tau7 Serpentis

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 56.29 ± 0.26 miliarcseconds/year towards the north and -73.22 ± 0.39 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Tau7 Serpentis

Tau7 Serpentis has a spectral type of A2m. This means the star is a blue star. The star is 7371.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24041.5000862400000000s. The star has a B-V Colour Index of 0.2 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 7,400 Kelvin.

Tau7 Serpentis Radius has been calculated as being 2.09 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,455,134.33.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.08. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Tau7 Serpentis Apparent and Absolute Magnitudes

Tau7 Serpentis has an apparent magnitude of 5.80 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 2.17 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.18. 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 Tau7 Serpentis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 18.78 which gave the calculated distance to Tau7 Serpentis as 173.68 light years away from Earth or 53.25 parsecs. It would take a spaceship travelling at the speed of light, 173.68 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 18.84 which put Tau7 Serpentis at a distance of 173.12 light years or 53.08 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 7,371.00 Parsecs or 24,041.50 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.

Tau7 Serpentis Facts

Alternative Names

Flamsteed Name22 Serpentis
Flamsteed Short Name22 Ser
Bayer DesignationTau7 Serpentis
Hipparcos Library I.D.76878
Bonner DurchmusterungBD+18 3059
Henry Draper Designation140232

Visual Facts

Star Type star
Absolute Magnitude2.17 / 2.18
Visual / Apparent Magnitude5.80
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)15h 41m 54.76
Declination (Dec.)+18d27`50.0
Galactic Latitude49.96 degrees
Galactic Longitude29.69 degrees
1997 Distance from Earth18.78 Parallax (milliarcseconds)
 173.68 Light Years
 53.25 Parsecs
2007 Revised Distance from Earth18.84 Parallax (milliarcseconds)
 173.12 Light Years
 53.08 Parsecs
Galacto-Centric Distance24,041.50 Light Years / 7,371.00 Parsecs
Proper Motion Dec.56.29 ± 0.26 milliarcseconds/year
Proper Motion RA.-73.22 ± 0.39 milliarcseconds/year
B-V Index0.20
Radial Velocity-27.80 ± 0.40 km/s
Spectral TypeA2m
Colour(A) blue

Estimated Facts

Calculated Effective Temperature7,400 Kelvin

Sources and Links

SIMBAD SourceLink

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