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Epsilon Monocerotis (8 Monocerotis) Star Facts

Epsilon Monocerotis Facts

  • Epsilon Monocerotis is a subgiant star that can be located in the constellation of Cetus. The description is based on the spectral class.
  • Epsilon Monocerotis is a main star of the constellation outline.
  • Based on the spectral type (A5IV) of the star, the star's colour is blue - white .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 122.30 light years away from us. Distance

Epsilon Monocerotis's Alternative Names

(Epsilon Monocerotis) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR2298. HIP30419 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD44769.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 8 Monocerotis. The Flamsteed name can be shortened to 8 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+04 1236.

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

Location of Epsilon Monocerotis

The location of the subgiant 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 object is compared to the celestial equator and is expressed in degrees. For Epsilon Monocerotis, the location is 06h 23m 46.10 and +04° 35` 34.2 .

Radial Velocity and Proper Motion of Epsilon Monocerotis

Proper Motion

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 10.91 ± 0.59 milliarcseconds/year towards the north and -22.06 ± 0.90 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is 13.10000 km/s with an error of about 0.80 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties of Epsilon Monocerotis

Epsilon Monocerotis Colour and Temperature

Based on the star's spectral type of A5IV , Epsilon Monocerotis's colour and type is blue - white subgiant star. The star has a B-V Colour Index of 0.21 which means the star's temperature is about 7,708 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Epsilon 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 20.40 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Epsilon Monocerotis Radius

Epsilon Monocerotis estimated radius has been calculated as being 2.74 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,903,226.94.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 2.6001899250178911530715429758. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

Epsilon Monocerotis Iron Abundance

Epsilon Monocerotis Iron Abundance is -0.11 with an error value of 0.04 Fe/H with the Sun has a value of 1 to put it into context. The value comes from the Hipparcos Extended Catalog.

Epsilon Monocerotis Apparent and Absolute Magnitudes

Epsilon Monocerotis has an apparent magnitude of 4.39 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 1.41 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.52. 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 Epsilon Monocerotis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 25.39000 which gave the calculated distance to Epsilon Monocerotis as 128.46 light years away from Earth or 39.39 parsecs. If you want that in miles, it is about 755,168,215,439,166.54, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 26.67000 which put Epsilon Monocerotis at a distance of 122.30 light years or 37.50 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.

Using the 2007 distance, the star is roughly 7,734,876.34 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun. The star's Galacto-Centric Distance is 7,434.00 Parsecs or 24,246.98 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Travel Time to Epsilon Monocerotis

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Walking420,504,103,431.68
Car120683,470,114.39
Airbus A380736111,435,344.74
Speed of Sound (Mach 1)767.269106,893,949.48
Concorde (Mach 2)1,534.5453,446,905.08
New Horizons Probe33,0002,485,345.87
Speed of Light670,616,629.00122.30

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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Additional Epsilon Monocerotis Facts and Figures

Visual Facts


Primary / Proper / Traditional NameEpsilon Monocerotis
Alternative NamesHD 44769, HIP 30419, HR 2298, 8 Monocerotis, 8 Mon, BD+04 1236
Spectral TypeA5IV
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeSubgiant Star
ColourBlue
GalaxyMilky Way
ConstellationCetus
Absolute Magnitude 1.41 / 1.52
Visual / Apparent Magnitude4.39
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)06h 23m 46.10
Declination (Dec.)+04° 35` 34.2
Galactic Latitude-4.03305513 degrees
Galactic Longitude205.67494988 degrees
1997 Distance from Earth25.39000 Parallax (milliarcseconds)
 128.46 Light Years
 39.39 Parsecs
2007 Distance from Earth26.67000 Parallax (milliarcseconds)
 122.30 Light Years
 37.50 Parsecs
 7,734,876.34 Astronomical Units
Galacto-Centric Distance24,246.98 Light Years / 7,434.00 Parsecs
Proper Motion Dec.10.91000 ± 0.59000 milliarcseconds/year
Proper Motion RA.-22.06000 ± 0.90000 milliarcseconds/year
B-V Index0.21
Radial Velocity13.10000 ± 0.80 km/s
Iron Abundance-0.1100 ± 0.04 Fe/H
Eccentricity0.12210
Semi-Major Axis8403.0000000
Stellar Luminosity (Lsun)20.4000000

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)2.60
Effective Temperature7,708 Kelvin

Sources and Links


SIMBAD SourceLink

Cetus Main Stars


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