Universe Guide

Polaris, Pole Star Facts

Polaris Facts

Information on Polaris

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.

Polaris hasn't always been the Pole Star, in 3,000 B.C., the Pole Star title was Thuban, a star in Draco. 3,000 B.C. was roughly about the time when the Great Pyramids were being built.

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.

At the other end of the night sky is Polaris Australis in the constellation of Octans is the closest you will get to a star being "under" the South Pole.

Polaris's Alternative Names

Alpha Ursae Minoris (Alf Umi) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in the early nineteenth century. The brightest star in the constellation is normally given the Alpha designation although there are exceptions such as Pollux which is Beta Geminorum.

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 objects' alternative names can be found at Star Names .

Location of Polaris

The location of the supergiant 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 Polaris, the location is 02h 31m 47.08 and +89° 15` 50.9 .

Radial Velocity and Proper Motion of Polaris

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 -11.85 ± 0.10 milliarcseconds/year towards the north and 44.48 ± 0.11 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 -16.42 km/s with an error of about 0.03 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.

Polaris 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 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.

Physical Properties (Colour, Temperature) of Polaris

Polaris Colour and Temperature

Polaris has a spectral type of F7:Ib-IIv SB. This means the star is a yellow to white supergiant 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 Radius

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 Apparent and Absolute Magnitudes

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.

Distance to Polaris

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.

Using the 2007 distance, the star is roughly 27,356,710.63 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 7,466.00 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*.

Variable Type of Polaris

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).

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 Polaris Facts and Figures

Visual Facts

Primary / Proper / Traditional NamePolaris
Alternative NamesAlpha Ursae Minoris, Alf Umi, Pole Star, HD 8890, HIP 11767, HR 424, 1 Ursae Minoris, 1 Umi, BD+88 8, alf UMi
Spectral TypeF7:Ib-IIv SB
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeLuminous Giant Star less luminour Supergiant Star
ColourYellow - White
GalaxyMilky Way
ConstellationUrsa Minor
Absolute Magnitude -3.64 / -3.64
Visual / Apparent Magnitude1.97
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)02h 31m 47.08
Declination (Dec.)+89° 15` 50.9
Galactic Latitude26.46 degrees
Galactic Longitude123.28 degrees
1997 Distance from Earth7.56 Parallax (milliarcseconds)
 431.43 Light Years
 132.28 Parsecs
2007 Distance from Earth7.54 Parallax (milliarcseconds)
 432.58 Light Years
 132.63 Parsecs
 27,356,710.63 Astronomical Units
Galacto-Centric Distance24,351.36 Light Years / 7,466.00 Parsecs
Proper Motion Dec.-11.85 ± 0.10 milliarcseconds/year
Proper Motion RA.44.48 ± 0.11 milliarcseconds/year
B-V Index0.63
Radial Velocity-16.42 ± 0.03 km/s
Iron Abundance0.13 ± 9.99 Fe/H
Semi-Major Axis6543.00
Stellar Luminosity (Lsun)2,634.12
Brightest in Night Sky48th
Associated / Clustered StarsPolaris Ab
Polaris B

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeDelta Cepheid
Mean Variability Period in Days3.971
Variable Magnitude Range (Brighter - Dimmer)2.093 - 2.124

Estimated Calculated Facts

Radius (x the Sun)49.32
Effective Temperature5,807 Kelvin

Sources and Links

SIMBAD SourceLink

Multi-Star System

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. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
8890+88 8.0A2.1000058.00000-4.00000F8Yellow/White

Location of Polaris in Ursa Minor

Polaris Location in Ursa Minor

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

Ursa Minor Main Stars

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