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Eta Mensae

Eta Mensae Facts

  • Eta Mensae is a giant star that can be located in the constellation of Mensa. The description is based on the spectral class.
  • Eta Mensae is a main star of the constellation outline.
  • Based on the spectral type (K6III) of the star, the star's colour is orange to red .
  • 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 668.37 light years away from us. Distance

Eta Mensae's Alternative Names

Eta Mensae (Eta Men) 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 HR1629. HIP22871 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD32440.

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

Location of Eta Mensae

The location of the giant 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 Eta Mensae, the location is 04h 55m 11.14 and -74° 56` 13.2 .

Radial Velocity and Proper Motion of Eta Mensae

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 61.52 ± 0.21 milliarcseconds/year towards the north and 28.27 ± 0.22 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 25.80000 km/s with an error of about 2.80 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 Eta Mensae

Eta Mensae Colour and Temperature

Based on the star's spectral type of K6III , Eta Mensae's colour and type is orange to red giant star. The star has a B-V Colour Index of 1.51 which means the star's temperature is about 3,971 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Eta Mensae 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 685.87 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Eta Mensae Radius

Eta Mensae estimated radius has been calculated as being 34.76 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 24,188,009.56.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 32.592249238354948709120711931. 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.

Eta Mensae Iron Abundance

Eta Mensae Iron Abundance is -0.22 with an error value of 0.07 Fe/H with the Sun has a value of 1 to put it into context. The value comes from the Hipparcos Extended Catalog.

Eta Mensae Apparent and Absolute Magnitudes

Eta Mensae has an apparent magnitude of 5.47 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 -1.23 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.09. 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 Eta Mensae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.58000 which gave the calculated distance to Eta Mensae as 712.15 light years away from Earth or 218.34 parsecs. If you want that in miles, it is about 4,186,463,059,512,707.86, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 4.88000 which put Eta Mensae at a distance of 668.37 light years or 204.92 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 42,267,489.57 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 7,352.00 Parsecs or 23,979.53 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 Eta Mensae

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)
Walking4112,055,009,081.18
Car1203,735,166,969.37
Airbus A380736608,994,614.57
Speed of Sound (Mach 1)767.269584,175,870.95
Concorde (Mach 2)1,534.54292,087,554.79
New Horizons Probe33,00013,582,425.34
Speed of Light670,616,629.00668.37

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 Eta Mensae Facts and Figures

Visual Facts


Primary / Proper / Traditional NameEta Mensae
Alternative NamesEta Men, HD 32440, HIP 22871, HR 1629
Spectral TypeK6III
Constellation's Main StarYes
Multiple Star SystemNo / Unknown
Star TypeGiant Star
ColourOrange to Red
GalaxyMilky Way
ConstellationMensa
Absolute Magnitude -1.23 / -1.09
Visual / Apparent Magnitude5.47
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)04h 55m 11.14
Declination (Dec.)-74° 56` 13.2
Galactic Latitude-33.55045820 degrees
Galactic Longitude287.11477358 degrees
1997 Distance from Earth4.58000 Parallax (milliarcseconds)
 712.15 Light Years
 218.34 Parsecs
2007 Distance from Earth4.88000 Parallax (milliarcseconds)
 668.37 Light Years
 204.92 Parsecs
 42,267,489.57 Astronomical Units
Galacto-Centric Distance23,979.53 Light Years / 7,352.00 Parsecs
Proper Motion Dec.61.52000 ± 0.21000 milliarcseconds/year
Proper Motion RA.28.27000 ± 0.22000 milliarcseconds/year
B-V Index1.51
Radial Velocity25.80000 ± 2.80 km/s
Iron Abundance-0.2200 ± 0.07 Fe/H
Eccentricity0.28710
Semi-Major Axis5823.0000000
Stellar Luminosity (Lsun)685.8700000

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)32.59
Effective Temperature3,971 Kelvin

Sources and Links


SIMBAD SourceLink

Location of Eta Mensae in Mensa


Eta Mensae Location in Mensa

The map was generated using Night Vision, an awesome free application by Brian Simpson.

Mensa Main Stars


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