Aludra (Eta Canis Majoris) is a blue very luminous supergiant star that can be located in the constellation of CanisMajor. Aludra is the 88th brightest star in the night sky and the 5th brightest star in Canis Major based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
Eta Canis Majoris is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR2827. HIP35904 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD58350.
Aludra has alternative name(s), eta CMa. In Arabic, it is known as Al-'Udhrah.
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 Aludra, the location is 07h 24m 05.71 and -29d18`11.2 .
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 5.81 ± 0.35 miliarcseconds/year towards the north and -4.14 ± 0.40 miliarcseconds/year east if we saw them in the horizon.
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 140000.0000000 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.
Aludra has a spectral type of B5Ia. This means the star is a blue supergiant star. The star has a B-V Colour Index of -0.08 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 12,939 Kelvin.
Aludra Radius has been calculated as being 59.04 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 41,082,809.35.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 36.74. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.
Aludra has an apparent magnitude of 2.45 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 -7.51 If you used the 2007 Parallax value, you would get an absolute magnitude of -6.48. 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.
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 1.02 which gave the calculated distance to Aludra as 3197.68 light years away from Earth or 980.39 parsecs. It would take a spaceship travelling at the speed of light, 3197.68 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 1.64 which put Aludra at a distance of 1988.80 light years or 609.76 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. Aludra brightness ranges from a magnitude of 2.478 to a magnitude of 2.382 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 days (variability).
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.
|Flamsteed Name||31 Canis Majoris|
|Flamsteed Short Name||31 CMa|
|Short Name||eta CMa|
|English Meaning||The maidenhead|
|Bayer Designation||Eta Canis Majoris|
|Hipparcos Library I.D.||35904|
|Yale Bright Star Catalogue (HR) Id||2827|
|Henry Draper Designation||58350|
|Star Type||supergiant star|
|Absolute Magnitude||-7.51 / -6.48|
|Visual / Apparent Magnitude||2.45|
|Naked Eye Visible||Yes - Magnitudes|
|Right Ascension (R.A.)||07h 24m 05.71|
|Galactic Latitude||-6.49 degrees|
|Galactic Longitude||242.62 degrees|
|1997 Distance from Earth||1.02 Parallax (milliarcseconds)|
|3197.68 Light Years|
|2007 Revised Distance from Earth||1.64 Parallax (milliarcseconds)|
|1988.80 Light Years|
|Proper Motion Dec.||5.81 ± 0.35 milliarcseconds/year|
|Proper Motion RA.||-4.14 ± 0.40 milliarcseconds/year|
|Radial Velocity||41.10 ± 2.50 km/s|
|Brightest in Night Sky||88th|
|Mean Variability Period in Days||0.079|
|Variable Magnitude Range (Brighter - Dimmer)||2.382 - 2.478|
|Luminosity (x the Sun)||140,000.0000000|
|Calculated Effective Temperature||12,939 Kelvin|
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. Id||B.D. Id||Star Code||Magnitude||R.A.||Dec.||Spectrum||Colour||Year|
The map was generated using Night Vision, an awesome free application by Brian Simpson.