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21 Monocerotis - HD55057 - HIP34724

21 Monocerotis is a blue to white pulsating main sequence dwarf star that can be located in the constellation of Monoceros. HIP34724 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD55057. 21 Monocerotis has alternative name(s), 21 Monocerotis , V571_Mon, 21 Mon.

Location of 21 Monocerotis

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 21 Monocerotis, the location is 07h 11m 23.63 and -00d18`06.9 .

Proper Motion of 21 Monocerotis

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 -010.45 ± 000.16 towards the north and -026.24 ± 000.25 east if we saw them in the horizon.

21 Monocerotis Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 4.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of 21 Monocerotis

21 Monocerotis has a spectral type of F2V. This means the star is a blue to white main sequence dwarf star. The star has a B-V Colour Index of 0.31 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 7,167 Kelvin.

21 Monocerotis has been calculated as 3.96 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,758,696.91.km.

21 Monocerotis Apparent and Absolute Magnitudes

21 Monocerotis has an apparent magnitude of 5.44 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 0.92 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.74. 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 21 Monocerotis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 12.49 which gave the calculated distance to 21 Monocerotis as 261.14 light years away from Earth or 80.06 parsecs. It would take a spaceship travelling at the speed of light, 261.14 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 11.47 which put 21 Monocerotis at a distance of 284.36 light years or 87.18 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 21 Monocerotis

The star is a pulsating Delta Scuti 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. 21 Monocerotis brightness ranges from a magnitude of 6.000 to a magnitude of 5.000 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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

21 Monocerotis Facts

Alternative Names

Traditional Name21 Monocerotis
Short NameV571 Mon, 21 Mon
Alternative Name(s)21 Monocerotis
Hipparcos Library I.D.34724
Bonner DurchmusterungBD-00 1634
Henry Draper Designation55057

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude0.92 / 0.74
Apparent Magnitude5.44
Right Ascension (R.A.)07h 11m 23.63
Declination (Dec.)-00d18`06.9
1997 Distance from Earth12.49 Parallax (milliarcseconds)
 261.14 Light Years
 80.06 Parsecs
2007 Revised Distance from Earth11.47 Parallax (milliarcseconds)
 284.36 Light Years
 87.18 Parsecs
Proper Motion Dec.-10.45 ± 0.16 milliarcseconds/year
Proper Motion RA.-26.24 ± 0.25 milliarcseconds/year
B-V Index0.31
Spectral TypeF2V
Colour(F) blue to white

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeDelta Scuti
Variable Magnitude Range (Brighter - Dimmer)5.000 - 6.000

Estimated Facts

Radius (x the Sun)3.96
Luminosity (x the Sun)4.0000000
Calculated Effective Temperature7,167 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars


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