Polaris (Alpha Ursae Minoris) is a blue to white pulsating luminous giant star that can be located in the constellation of UrsaMinor. It is the 49th brightest star in the night sky. Alpha Ursae Minoris is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR424. HIP11767 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD8890. Polaris has alternative name(s), 1 Ursae Minoris , alf_UMi, 1 UMi.
Polaris is the most important star used for navigation, if you can locate the star, then you have a good idea of which direction is north. Polaris is the star nearly directly up from the North Pole in the Arctic hence why it is also known as the "North Star" in addition to being the "Pole Star". If you was to take a picture of the night sky so that you had star trails, If you then looked at all the photos, you would see that Polar stays still. Although it is the brightest star in the constellation, it is nowhere near being the brightest star in the night star, it is still bright but its only at position 45.
Over time, Polaris will loose its title and Vega will gain the title in 13,000 years. Its a long way off so no need to worry about it. Then another 13,000 years after that, Polaris will regain its title as the Pole Star.Ref: N.A.S.A.
It is multiple star system with two stars close by, one nearby Polaris Ab and the other just a little further out Polaris B. There are also two distant stars in this system, C and D but are not as well documented at the closest.
Polaris is also the name given to the nuclear missiles that were used by the Royal Navy submarines of the United Kingdom of the sixties to the nineties. The missiles were then replaced by the Trident nuclear system.
It is relatively easy to locate if you know what you are looking for. If you first look for the distinctive Ursa Major first and then use the two stars on the right of the plough part, Merak and Dubhe and then fellow up from those stars in a line, you will come across Polaris.
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 Polaris, the location is 02h 31m 47.08 and +89d15`50.9 .
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 -011.85 ± 000.10 towards the north and 044.48 ± 000.11 east if we saw them in the horizon.
Polaris has a spectral type of F7:Ib-IIv SB. This means the star is a blue to white luminous giant star. The star has a B-V Colour Index of 0.63 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,807 Kelvin.
Polaris has been calculated as 49.32 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 34,317,837.54.km.
The star has companion stars which are in orbit close by, it has at least the following companions in close orbit, Polaris Ab, Polaris B.
Polaris has an apparent magnitude of 1.97 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 -3.64 If you used the 2007 Parallax value, you would get an absolute magnitude of -3.64. 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 7.56 which gave the calculated distance to Polaris as 431.43 light years away from Earth or 132.28 parsecs. It would take a spaceship travelling at the speed of light, 431.43 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 7.54 which put Polaris at a distance of 432.58 light years or 132.63 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 is a pulsating Delta Cepheid 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. Polaris brightness ranges from a magnitude of 2.000 to a magnitude of 2.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 4.0 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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.
|Short Name||alf UMi, 1 UMi|
|Bayer Designation||Alpha Ursae Minoris|
|Alternative Name(s)||1 Ursae Minoris|
|Hipparcos Library I.D.||11767|
|Yale Bright Star Catalogue (HR) Id||424|
|Bonner Durchmusterung||BD+88 8|
|Henry Draper Designation||8890|
|Star Type||luminous giant star|
|Absolute Magnitude||-3.64 / -3.64|
|Right Ascension (R.A.)||02h 31m 47.08|
|1997 Distance from Earth||7.56 Parallax (milliarcseconds)|
|431.43 Light Years|
|2007 Revised Distance from Earth||7.54 Parallax (milliarcseconds)|
|432.58 Light Years|
|Proper Motion Dec.||-11.85 ± 0.10 milliarcseconds/year|
|Proper Motion RA.||44.48 ± 0.11 milliarcseconds/year|
|Spectral Type||F7:Ib-IIv SB|
|Brightest in Night Sky||49th|
|Colour||(F) blue to white|
|Companion Stars||Polaris Ab|
|Variable Star Class||Pulsating|
|Variable Star Type||Delta Cepheid|
|Mean Variability Period in Days||4.000|
|Radius (x the Sun)||49.32|
|Calculated Effective Temperature||5,807 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|