RT Lacertae is a white to yellow eclipsing subgiant star that can be located in the constellation of Lacerta. HIP108728 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD209318. RT Lacertae has alternative name(s), RT_Lac.
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 RT Lacertae, the location is 22h 01m 30.69 and +43d53`25.5 .
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 021.27 ± 000.93 towards the north and 056.32 ± 001.17 east if we saw them in the horizon.
RT Lacertae has a spectral type of G9IV + K1IV. This means the star is a white to yellow subgiant star. The star has a B-V Colour Index of 1.07 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,718 Kelvin.
RT Lacertae has been calculated as 4.40 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,060,887.13.km.
RT Lacertae has an apparent magnitude of 8.93 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 2.51 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.91. 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.
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 5.19 which gave the calculated distance to RT Lacertae as 628.45 light years away from Earth or 192.68 parsecs. It would take a spaceship travelling at the speed of light, 628.45 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 3.95 which put RT Lacertae at a distance of 825.73 light years or 253.16 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 is a eclipsing Beta Lyrae (Sheliak)/RS Canum Venaticorum-type binary systems 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. RT Lacertae brightness ranges from a magnitude of 10.000 to a magnitude of 9.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 5.0 days (variability).
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.
|Traditional Name||RT Lacertae|
|Short Name||RT Lac|
|Hipparcos Library I.D.||108728|
|Bonner Durchmusterung||BD+43 4112|
|Henry Draper Designation||209318|
|Star Type||subgiant star|
|Absolute Magnitude||2.51 / 1.91|
|Right Ascension (R.A.)||22h 01m 30.69|
|1997 Distance from Earth||5.19 Parallax (milliarcseconds)|
|628.45 Light Years|
|2007 Revised Distance from Earth||3.95 Parallax (milliarcseconds)|
|825.73 Light Years|
|Proper Motion Dec.||21.27 ± 0.93 milliarcseconds/year|
|Proper Motion RA.||56.32 ± 1.17 milliarcseconds/year|
|Spectral Type||G9IV + K1IV|
|Colour||(G) White to Yellow|
|Variable Star Class||Eclipsing|
|Variable Star Type||Beta Lyrae (Sheliak)/RS Canum Venaticorum-type binary systems|
|Mean Variability Period in Days||5.000|
|Variable Magnitude Range (Brighter - Dimmer)||9.000 - 10.000|
|Radius (x the Sun)||4.40|
|Calculated Effective Temperature||4,718 Kelvin|