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W Serpentis, HD166126, HIP88994

W Serpentis is a blue to white eclipsing supergiant star that can be located in the constellation of Serpens. The description is based on the spectral class. W Serpentis is not part of the constellation but is within the borders of the constellation.

The star can not be seen by the naked eye, you need a telescope to see it.

W Serpentis's Alternative Names

HIP88994 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD166126.

W Serpentis has alternative name(s) :- , W Ser.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD-15 4842.

More details on star alternative names can be found at Star Names .

Location of W Serpentis

The location of the star in the night sky 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 W Serpentis, the location is 18h 09m 50.65 and -15° 33` 00.3 .

Radial Velocity and Proper Motion of W 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 0.82 ± 0.56 miliarcseconds/year towards the north and 6.24 ± 0.99 miliarcseconds/year east if we saw them in the horizon.

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is 18.60 km/s with an error of about 10.00 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties (Colour, Temperature) of W Serpentis

W Serpentis has a spectral type of F8/G2Iaep+A:. This means the star is a blue to white supergiant star. The star has a B-V Colour Index of 0.69 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,671 Kelvin.

W Serpentis Radius has been calculated as being 6.10 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 4,246,769.78.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 23.53. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

W Serpentis Apparent and Absolute Magnitudes

W Serpentis has an apparent magnitude of 8.84 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 1.00 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.93. 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 W Serpentis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 2.70 which gave the calculated distance to W Serpentis as 1208.01 light years away from Earth or 370.37 parsecs. It would take a spaceship travelling at the speed of light, 1208.01 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 0.70 which put W Serpentis at a distance of 4659.48 light years or 1428.57 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.

Using the 2007 distance, the star is roughly 294,661,661.03 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun.

Variable Type of W Serpentis

The star is a eclipsing Beta Persei (Algol)/ 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. W Serpentis brightness ranges from a magnitude of 9.730 to a magnitude of 8.720 over its variable period. The smaller the magnitude, the brighter the star.

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.

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W Serpentis Facts

Visual Facts


Primary / Proper / Traditional NameW Serpentis
Alternative NamesHD 166126, HIP 88994, BD-15 4842, W Ser
Spectral TypeF8/G2Iaep+A:
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star Type very luminous Supergiant Star
Colour blue to white
GalaxyMilky Way
ConstellationSerpens
Absolute Magnitude 1.00 / -1.93
Visual / Apparent Magnitude8.84
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)18h 09m 50.65
Declination (Dec.)-15° 33` 00.3
Galactic Latitude1.86 degrees
Galactic Longitude14.39 degrees
1997 Distance from Earth2.70 Parallax (milliarcseconds)
 1208.01 Light Years
 370.37 Parsecs
2007 Distance from Earth0.70 Parallax (milliarcseconds)
 4659.48 Light Years
 1428.57 Parsecs
 294,661,661.03 Astronomical Units
Proper Motion Dec.0.82 ± 0.56 milliarcseconds/year
Proper Motion RA.6.24 ± 0.99 milliarcseconds/year
B-V Index0.69
Radial Velocity18.60 ± 10.00 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEclipsing
Variable Star TypeBeta Persei (Algol)/
Variable Magnitude Range (Brighter - Dimmer)8.720 - 9.730

Estimated Facts


Calculated Effective Temperature5,671 Kelvin

Sources and Links


SIMBAD SourceLink

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