Polaris (Alpha Ursae Minoris) is a blue to white pulsating luminous giant star that can be located in the constellation of Ursa Minor. The description is based on the spectral class. Polaris is the 48th brightest star in the night sky and is the brightest star in Ursa Minor 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.
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.
Alpha Ursae Minoris (Alf Umi) 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) :- Pole Star, alf UMi.
Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 1 Ursae Minoris with it shortened to 1 UMi.
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+88 8.
More details on star alternative names can be found at Star Names .
The location of the 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 star is compared to the celestial equator and is expressed in degrees. For Polaris, the location is 02h 31m 47.08 and +89° 15` 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 -11.85 ± 0.10 miliarcseconds/year towards the north and 44.48 ± 0.11 miliarcseconds/year east if we saw them in the horizon. The Radial Velocity, that is the speed at which the star is moving away/towards us is -16.42000 km/s with an error of about 0.03 km/s .
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 2,634.12 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.
Polaris has a spectral type of F7:Ib-IIv SB. This means the star is a blue to white luminous giant star. The star is 7,466.00 Parsecs from the Galactic Centre or terms of Light Years is 24,351.36 s. 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 Radius has been calculated as being 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. 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 49.32. 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 0.13 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.
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's Galacto-Centric Distance is 7,466.00 Parsecs or 24,351.36 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.
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 2.124 to a magnitude of 2.093 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 Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.
|Primary / Proper / Traditional Name||Polaris|
|Alternative Names||Alpha Ursae Minoris, Alf Umi, Pole Star, HD 8890, HIP 11767, HR 424, 1 Ursae Minoris, 1 UMi, BD+88 8, alf UMi|
|Spectral Type||F7:Ib-IIv SB|
|Multiple Star System||Yes|
|Star Type||Luminous Giant Star|
|Colour||blue to white|
|Absolute Magnitude||-3.64 / -3.64|
|Visual / Apparent Magnitude||1.97|
|Naked Eye Visible||Yes - Magnitudes|
|Right Ascension (R.A.)||02h 31m 47.08|
|Declination (Dec.)||+89° 15` 50.9|
|Galactic Latitude||26.46 degrees|
|Galactic Longitude||123.28 degrees|
|1997 Distance from Earth||7.56 Parallax (milliarcseconds)|
|431.43 Light Years|
|2007 Distance from Earth||7.54 Parallax (milliarcseconds)|
|432.58 Light Years|
|Galacto-Centric Distance||24,351.36 Light Years / 7,466.00 Parsecs|
|Proper Motion Dec.||-11.85 ± 0.10 milliarcseconds/year|
|Proper Motion RA.||44.48 ± 0.11 milliarcseconds/year|
|Radial Velocity||-16.42 ± 0.03 km/s|
|Iron Abundance||0.13 ± 9.99 Fe/H|
|Stellar Luminosity (Lsun)||2,634.12|
|Brightest in Night Sky||48th|
|Associated / Clustered Stars||Polaris Ab|
|Variable Star Class||Pulsating|
|Variable Star Type||Delta Cepheid|
|Mean Variability Period in Days||3.971|
|Variable Magnitude Range (Brighter - Dimmer)||2.093 - 2.124|
|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|