Alkaid (Eta Ursae Majoris) - HD120315 - HIP67301 - HR5191

Alkaid (Eta Ursae Majoris) is a blue main sequence dwarf star that can be located in the constellation of UrsaMajor. It is the 41st brightest star in the night sky. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Eta Ursae Majoris is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR5191. HIP67301 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD120315.

Alkaid has alternative name(s), Benetnash, Benetnasch,[10] Elkeid, Eta UMa, 85 Ursae Majoris , 85 UMa. In Arabic, it is known as Al-Qa'id.

Location of Alkaid

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 Alkaid, the location is 13h 47m 32.55 and +49d18`47.9 .

Proper Motion of Alkaid

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 -14.91 ± 0.19 miliarcseconds/year towards the north and -121.17 ± 0.24 miliarcseconds/year east if we saw them in the horizon.

Alkaid 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 1060.0000000 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.

Physical Properties (Colour, Temperature, Radius) of Alkaid

Alkaid has a spectral type of B3V SB. This means the star is a blue main sequence dwarf star. The star is 7403.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24145.8723563200000000s. The star has a B-V Colour Index of -0.09 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 11,375 Kelvin.

Alkaid Radius has been calculated as being 3.17 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,205,417.98.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.27. 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 -0.14 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Alkaid Apparent and Absolute Magnitudes

Alkaid has an apparent magnitude of 1.85 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 -0.60 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.67. 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 Alkaid

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 32.39 which gave the calculated distance to Alkaid as 100.70 light years away from Earth or 30.87 parsecs. It would take a spaceship travelling at the speed of light, 100.70 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 31.38 which put Alkaid at a distance of 103.94 light years or 31.87 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 7,403.00 Parsecs or 24,145.87 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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.