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18 Ursae Majoris, HD79439, HIP45493, HR3662

18 Ursae Majoris is a blue main sequence dwarf star that can be located in the constellation of UrsaMajor. 18 Ursae Majoris is the brightest star in Ursa 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.

The Id of the star in the Yale Bright Star Catalogue is HR3662. HIP45493 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD79439.

Location of 18 Ursae Majoris

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 18 Ursae Majoris, the location is 09h 16m 11.28 and +54d 01` 18.2 .

Proper Motion of 18 Ursae Majoris

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 59.92 ± 0.12 miliarcseconds/year towards the north and 49.43 ± 0.20 miliarcseconds/year east if we saw them in the horizon.

18 Ursae Majoris 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 11.0000000 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 18 Ursae Majoris

18 Ursae Majoris has a spectral type of A5V. This means the star is a blue main sequence dwarf star. The star is 7425.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24217.6282920000000000s. The star has a B-V Colour Index of 0.19 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 7,827 Kelvin.

18 Ursae Majoris Radius has been calculated as being 2.02 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,406,622.39.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 1.99. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

18 Ursae Majoris Apparent and Absolute Magnitudes

18 Ursae Majoris has an apparent magnitude of 4.80 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 2.00 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.03. 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 18 Ursae Majoris

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 27.55 which gave the calculated distance to 18 Ursae Majoris as 118.39 light years away from Earth or 36.30 parsecs. It would take a spaceship travelling at the speed of light, 118.39 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 27.90 which put 18 Ursae Majoris at a distance of 116.90 light years or 35.84 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 7,425.00 Parsecs or 24,217.63 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.

18 Ursae Majoris Facts

Alternative Names

Traditional/Proper Name18 Ursae Majoris
Flamsteed Name18 Ursae Majoris
Flamsteed Short Name18 UMa
Hipparcos Library I.D.45493
Yale Bright Star Catalogue (HR) Id3662
Bonner DurchmusterungBD+54 1285
Henry Draper Designation79439

Visual Facts

Star Typemain sequence dwarf star
ConstellationUrsa Major
Absolute Magnitude2.00 / 2.03
Visual / Apparent Magnitude4.80
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)09h 16m 11.28
Declination (Dec.)+54d 01` 18.2
Galactic Latitude42.66 degrees
Galactic Longitude163.08 degrees
1997 Distance from Earth27.55 Parallax (milliarcseconds)
 118.39 Light Years
 36.30 Parsecs
2007 Revised Distance from Earth27.90 Parallax (milliarcseconds)
 116.90 Light Years
 35.84 Parsecs
Galacto-Centric Distance24,217.63 Light Years / 7,425.00 Parsecs
Proper Motion Dec.59.92 ± 0.12 milliarcseconds/year
Proper Motion RA.49.43 ± 0.20 milliarcseconds/year
B-V Index0.19
Radial Velocity-17.50 ± 0.90 km/s
Spectral TypeA5V
Colour(A) blue

Estimated Facts

Luminosity (x the Sun)11.0000000
Calculated Effective Temperature7,827 Kelvin

Sources and Links

SIMBAD SourceLink

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