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SW Lacertae, HD216598, HIP113052

SW Lacertae is a orange to red eclipsing main sequence dwarf star that can be located in the constellation of Lacerta. SW Lacertae is the brightest star in Lacerta based on the Hipparcos 2007 apparent magnitude. The star can not be seen by the naked eye, you need a telescope to see it.

HIP113052 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD216598.

SW Lacertae has alternative name(s), SW Lac.

Location of SW Lacertae

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 SW Lacertae, the location is 22h 53m 41.59 and +37d56`18.5 .

Proper Motion of SW Lacertae

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 12.89 ± 0.94 miliarcseconds/year towards the north and 87.93 ± 1.80 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of SW Lacertae

SW Lacertae has a spectral type of K0Vvar. This means the star is a orange to red main sequence dwarf star. The star is 7412.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24175.2270572800000000s. The star has a B-V Colour Index of 0.75 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,418 Kelvin.

SW Lacertae Radius has been calculated as being 1.43 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 994,642.75.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 1.27. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

SW Lacertae Apparent and Absolute Magnitudes

SW Lacertae has an apparent magnitude of 8.90 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 4.35 If you used the 2007 Parallax value, you would get an absolute magnitude of 4.60. 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 SW Lacertae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 12.30 which gave the calculated distance to SW Lacertae as 265.17 light years away from Earth or 81.30 parsecs. It would take a spaceship travelling at the speed of light, 265.17 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 13.79 which put SW Lacertae at a distance of 236.52 light years or 72.52 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 7,412.00 Parsecs or 24,175.23 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of SW Lacertae

The star is a eclipsing W Ursae Majoris/Contact systems of the W UMa type, with ellipsoidal components of F0-K spectral type 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. SW Lacertae brightness ranges from a magnitude of 9.575 to a magnitude of 8.798 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.3 days (variability).

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.

SW Lacertae Facts

Alternative Names

Traditional/Proper NameSW Lacertae
Short NameSW Lac
Hipparcos Library I.D.113052
Bonner DurchmusterungBD+37 4717
Henry Draper Designation216598

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude4.35 / 4.60
Visual / Apparent Magnitude8.90
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)22h 53m 41.59
Declination (Dec.)+37d56`18.5
Galactic Latitude-19.33 degrees
Galactic Longitude98.68 degrees
1997 Distance from Earth12.30 Parallax (milliarcseconds)
 265.17 Light Years
 81.30 Parsecs
2007 Revised Distance from Earth13.79 Parallax (milliarcseconds)
 236.52 Light Years
 72.52 Parsecs
Galacto-Centric Distance24,175.23 Light Years / 7,412.00 Parsecs
Proper Motion Dec.12.89 ± 0.94 milliarcseconds/year
Proper Motion RA.87.93 ± 1.80 milliarcseconds/year
B-V Index0.75
Radial Velocity-14.46 ± 0.90 km/s
Spectral TypeK0Vvar
Colour(K) Orange to Red

Variable Star Details

Variable Star ClassEclipsing
Variable Star TypeW Ursae Majoris/Contact systems of the W UMa type, with ellipsoidal components of F0-K spectral type
Mean Variability Period in Days0.321
Variable Magnitude Range (Brighter - Dimmer)8.798 - 9.575

Estimated Facts

Calculated Effective Temperature5,418 Kelvin

Sources and Links

SIMBAD SourceLink

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