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RW Monocerotis, HD259986, HIP31383

RW Monocerotis is a blue eclipsing main sequence dwarf star that can be located in the constellation of Monoceros. The description is based on the spectral class. The star can not be seen by the naked eye, you need a telescope to see it.

RW Monocerotis's Alternative Names

HIP31383 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD259986.

RW Monocerotis has alternative name(s) :- , RW Mon.

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+08 1402.

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

Location of RW Monocerotis

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 RW Monocerotis, the location is 06h 34m 45.89 and +08° 49` 32.2 .

Proper Motion of RW 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 -5.41 ± 0.93 miliarcseconds/year towards the north and -7.83 ± 1.59 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 us is 4.30000 km/s with an error of about 7.40 km/s .

Physical Properties (Colour, Temperature) of RW Monocerotis

RW Monocerotis has a spectral type of B8V. This means the star is a blue main sequence dwarf star. The star has a B-V Colour Index of 0.06 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 8,815 Kelvin.

RW Monocerotis Radius has been calculated as being 1.27 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 880,883.86.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 1.24. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

RW Monocerotis Apparent and Absolute Magnitudes

RW Monocerotis has an apparent magnitude of 9.31 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 2.50 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.54. 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 RW Monocerotis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.35 which gave the calculated distance to RW Monocerotis as 749.80 light years away from Earth or 229.89 parsecs. It would take a spaceship travelling at the speed of light, 749.80 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 4.42 which put RW Monocerotis at a distance of 737.93 light years or 226.24 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 RW Monocerotis

The star is a eclipsing Beta Persei (Algol)/Semi-Detached System (subtype) 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. RW Monocerotis brightness ranges from a magnitude of 11.500 to a magnitude of 9.290 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 1.9 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.

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RW Monocerotis Facts

Visual Facts


Primary / Proper / Traditional NameRW Monocerotis
Alternative NamesHD 259986, HIP 31383, BD+08 1402, RW Mon
Spectral TypeB8V
Multiple Star SystemNo / Unknown
Star Type main sequence Dwarf Star
Colour blue
GalaxyMilky Way
ConstellationMonoceros
Absolute Magnitude2.50 / 2.54
Visual / Apparent Magnitude9.31
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)06h 34m 45.89
Declination (Dec.)+08° 49` 32.2
Galactic Latitude0.35 degrees
Galactic Longitude203.18 degrees
1997 Distance from Earth4.35 Parallax (milliarcseconds)
 749.80 Light Years
 229.89 Parsecs
2007 Distance from Earth4.42 Parallax (milliarcseconds)
 737.93 Light Years
 226.24 Parsecs
Proper Motion Dec.-5.41 ± 0.93 milliarcseconds/year
Proper Motion RA.-7.83 ± 1.59 milliarcseconds/year
B-V Index0.06
Radial Velocity4.30 ± 7.40 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEclipsing
Variable Star TypeBeta Persei (Algol)/Semi-Detached System (subtype)
Mean Variability Period in Days1.906
Variable Magnitude Range (Brighter - Dimmer)9.290 - 11.500

Estimated Facts


Calculated Effective Temperature8,815 Kelvin

Sources and Links


SIMBAD SourceLink

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