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S Monocerotis, 15 Monocerotis, HD47839, HIP31978, HR2456

S Monocerotis is a blue pulsating variable star that can be located in the constellation of Monoceros. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

S Monocerotis's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR2456. HIP31978 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD47839.

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

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 15 Monocerotis with it shortened to 15 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+10 1220.

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

Location of S 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 S Monocerotis, the location is 06h 40m 58.66 and +09° 53` 44.7 .

Proper Motion of S 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 -1.61 ± 0.29 miliarcseconds/year towards the north and -2.61 ± 0.50 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 22.00000 km/s with an error of about 0.30 km/s .

S 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 5,732.04 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of S Monocerotis

S Monocerotis has a spectral type of O7. This means the star is a blue variable star. The star is 7,654.00 Parsecs from the Galactic Centre or terms of Light Years is 24,964.54 s. The star has a B-V Colour Index of -0.23 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 25,232 Kelvin.

S Monocerotis Radius has been calculated as being 1.79 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,245,983.13.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 1.61. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.04 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

S Monocerotis Apparent and Absolute Magnitudes

S Monocerotis has an apparent magnitude of 4.66 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 -2.82 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.59. 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 S Monocerotis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 3.19 which gave the calculated distance to S Monocerotis as 1022.46 light years away from Earth or 313.48 parsecs. It would take a spaceship travelling at the speed of light, 1022.46 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 3.55 which put S Monocerotis at a distance of 918.77 light years or 281.69 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 7,654.00 Parsecs or 24,964.54 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 S Monocerotis

The star is a pulsating Semi-Regular Star which are giants or supergiants of intermediate and late spectral 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. S Monocerotis brightness ranges from a magnitude of 4.567 to a magnitude of 4.532 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.0 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.

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S Monocerotis Facts

Visual Facts

Primary / Proper / Traditional NameS Monocerotis
Alternative NamesS Mon, HD 47839, HIP 31978, HR 2456, 15 Monocerotis, 15 Mon, BD+10 1220, S Mon
Spectral TypeO7
Multiple Star SystemYes
Star TypeVariable Star
Colour blue
GalaxyMilky Way
Absolute Magnitude-2.82 / -2.59
Visual / Apparent Magnitude4.66
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)06h 40m 58.66
Declination (Dec.)+09° 53` 44.7
Galactic Latitude2.20 degrees
Galactic Longitude202.94 degrees
1997 Distance from Earth3.19 Parallax (milliarcseconds)
 1022.46 Light Years
 313.48 Parsecs
2007 Distance from Earth3.55 Parallax (milliarcseconds)
 918.77 Light Years
 281.69 Parsecs
Galacto-Centric Distance24,964.54 Light Years / 7,654.00 Parsecs
Proper Motion Dec.-1.61 ± 0.29 milliarcseconds/year
Proper Motion RA.-2.61 ± 0.50 milliarcseconds/year
B-V Index-0.23
Radial Velocity22.00 ± 0.30 km/s
Iron Abundance0.04 ± 9.99 Fe/H
Semi-Major Axis8564.00
Stellar Luminosity (Lsun)5,732.04

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSemi-Regular Star which are giants or supergiants of intermediate and late spectral
Mean Variability Period in Days0.034
Variable Magnitude Range (Brighter - Dimmer)4.532 - 4.567

Estimated Facts

Calculated Effective Temperature25,232 Kelvin

Sources and Links

SIMBAD SourceLink

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.

Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
47839+10 1220.0A4.70000-1.00000-4.00000O5Blue
261878+09 1338.0F7.80000-14.00000-18.00000A0White1985
261841+09 1336.0FG8.30000A0White1985
261938+10 1223.0H10.70000-21.00000-3.00000B9Blue/White1985
+10 1222.0HJ10.800001985
261937+10 1224.0K8.20000F0Yellow/White1985
261969+10 1227.0L10.20000B9Blue/White1985

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