Universe Guide


73 Orionis, HD43247, HIP29736

73 Orionis is a blue giant star that can be located in the constellation of Orion. 73 Orionis is the brightest star in Orion 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.

HIP29736 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD43247.

Location of 73 Orionis

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 73 Orionis, the location is 06h 15m 44.97 and +12d33`03.9 .

Proper Motion of 73 Orionis

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 -1.10 ± 0.20 miliarcseconds/year towards the north and -1.80 ± 0.31 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of 73 Orionis

73 Orionis has a spectral type of B9II-III. This means the star is a blue giant star. The star is 7736.00000000 Parsecs from the Galactic Centre or terms of Light Years is 25231.9962918400000000s. The star has a B-V Colour Index of 0.01 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 9,392 Kelvin.

73 Orionis Radius has been calculated as being 12.34 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 8,588,125.18.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 10.27. 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 -0.02 with an error value of 0.04 Fe/H with the Sun has a value of 1 to put it into context.

73 Orionis Apparent and Absolute Magnitudes

73 Orionis has an apparent magnitude of 5.44 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 -2.72 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.32. 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 73 Orionis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 2.33 which gave the calculated distance to 73 Orionis as 1399.84 light years away from Earth or 429.18 parsecs. It would take a spaceship travelling at the speed of light, 1399.84 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 2.80 which put 73 Orionis at a distance of 1164.87 light years or 357.14 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 7,736.00 Parsecs or 25,232.00 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.

73 Orionis Facts

Alternative Names

Traditional/Proper Name73 Orionis
Flamsteed Name73 Orionis
Flamsteed Short Name73 Ori
Hipparcos Library I.D.29736
Bonner DurchmusterungBD+12 1081
Henry Draper Designation43247

Visual Facts

Star Typegiant star
Absolute Magnitude-2.72 / -2.32
Visual / Apparent Magnitude5.44
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)06h 15m 44.97
Declination (Dec.)+12d33`03.9
Galactic Latitude-2.04 degrees
Galactic Longitude197.71 degrees
1997 Distance from Earth2.33 Parallax (milliarcseconds)
 1399.84 Light Years
 429.18 Parsecs
2007 Revised Distance from Earth2.80 Parallax (milliarcseconds)
 1164.87 Light Years
 357.14 Parsecs
Galacto-Centric Distance25,232.00 Light Years / 7,736.00 Parsecs
Proper Motion Dec.-1.10 ± 0.20 milliarcseconds/year
Proper Motion RA.-1.80 ± 0.31 milliarcseconds/year
B-V Index0.01
Radial Velocity12.90 ± 1.20 km/s
Iron Abundance-0.02 ± 0.04 Fe/H
Spectral TypeB9II-III
Colour(B) blue

Estimated Facts

Calculated Effective Temperature9,392 Kelvin

Sources and Links

SIMBAD SourceLink

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