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RT Lacertae - HD209318 - HIP108728

RT Lacertae is a white to yellow eclipsing subgiant star that can be located in the constellation of Lacerta. The star can not be seen by the naked eye, you need a telescope to see it.

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.

Location of RT 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 RT Lacertae, the location is 22h 01m 30.69 and +43d53`25.5 .

Proper Motion of RT 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 21.27 ± 0.93 miliarcseconds/year towards the north and 56.32 ± 1.17 miliarcseconds/year east if we saw them in the horizon.

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

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 Radius has been calculated as being 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. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 5.80. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

RT Lacertae Apparent and Absolute Magnitudes

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.

Distance to RT Lacertae

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.

Variable Type of RT Lacertae

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).

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.

RT Lacertae Facts

Alternative Names

Traditional/Proper NameRT Lacertae
Short NameRT Lac
Hipparcos Library I.D.108728
Bonner DurchmusterungBDD+43 4112
Henry Draper Designation209318

Visual Facts

Star Typesubgiant star
Absolute Magnitude2.51 / 1.91
Visual / Apparent Magnitude8.93
Naked Eye VisibleRequires a 7x50 Binoculars - Ref: Wiki
Right Ascension (R.A.)22h 01m 30.69
Declination (Dec.)+43d53`25.5
Galactic Latitude-9.03 degrees
Galactic Longitude93.41 degrees
1997 Distance from Earth5.19 Parallax (milliarcseconds)
 628.45 Light Years
 192.68 Parsecs
2007 Revised Distance from Earth3.95 Parallax (milliarcseconds)
 825.73 Light Years
 253.16 Parsecs
Proper Motion Dec.21.27 ± 0.93 milliarcseconds/year
Proper Motion RA.56.32 ± 1.17 milliarcseconds/year
B-V Index1.07
Radial Velocity-53.26 ± 0.78 km/s
Spectral TypeG9IV + K1IV
Colour(G) White to Yellow

Variable Star Details

Variable Star ClassEclipsing
Variable Star TypeBeta Lyrae (Sheliak)/RS Canum Venaticorum-type binary systems
Mean Variability Period in Days5.000
Variable Magnitude Range (Brighter - Dimmer)9.000 - 10.000

Estimated Facts

Calculated Effective Temperature4,718 Kelvin

Sources and Links

SIMBAD SourceLink

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