Universe Guide


Ras Alhague (Alpha Ophiuchi) - HD159561 - HIP86032 - HR6556

Ras Alhague (Alpha Ophiuchi) is a blue giant star that can be located in the constellation of Ophiuchus. It is the 57th brightest star in the night sky. Alpha Ophiuchi is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR6556. HIP86032 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD159561. Ras Alhague has alternative name(s), 55 Ophiuchi , 55 Oph. In Arabic, it is known as Ra's al-Hawwa'.

Location of Ras Alhague

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 Ras Alhague, the location is 17h 34m 56.00 and +12d33`38.1 .

Proper Motion of Ras Alhague

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 -221.57 ± 000.71 towards the north and 108.07 ± 001.06 east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Ras Alhague

Ras Alhague has a spectral type of A5III. This means the star is a blue giant star. The star has a B-V Colour Index of 0.15 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 8,084 Kelvin.

Ras Alhague has been calculated as 2.62 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,820,214.03.km.

Ras Alhague Apparent and Absolute Magnitudes

Ras Alhague has an apparent magnitude of 2.08 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 1.30 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.21. 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 Ras Alhague

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 69.84 which gave the calculated distance to Ras Alhague as 46.70 light years away from Earth or 14.32 parsecs. It would take a spaceship travelling at the speed of light, 46.70 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 67.13 which put Ras Alhague at a distance of 48.59 light years or 14.90 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.

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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Ras Alhague Facts

Alternative Names

Traditional NameRas Alhague
Short Name55 Oph
Arabic NameRa's al-Hawwa'
English MeaningHead of the snake-man
Bayer DesignationAlpha Ophiuchi
Alternative Name(s)55 Ophiuchi
Hipparcos Library I.D.86032
Yale Bright Star Catalogue (HR) Id6556
Bonner DurchmusterungBD+12 3252
Henry Draper Designation159561

Visual Facts

Star Typegiant star
Absolute Magnitude1.30 / 1.21
Apparent Magnitude2.08
Right Ascension (R.A.)17h 34m 56.00
Declination (Dec.)+12d33`38.1
1997 Distance from Earth69.84 Parallax (milliarcseconds)
 46.70 Light Years
 14.32 Parsecs
2007 Revised Distance from Earth67.13 Parallax (milliarcseconds)
 48.59 Light Years
 14.90 Parsecs
Proper Motion Dec.-221.57 ± 0.71 milliarcseconds/year
Proper Motion RA.108.07 ± 1.06 milliarcseconds/year
B-V Index0.15
Spectral TypeA5III
Brightest in Night Sky57th
Colour(A) blue

Estimated Facts

Radius (x the Sun)2.62
Calculated Effective Temperature8,084 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Location of Ras Alhague in Ophiuchus

Ras Alhague (Alpha Ophiuchi) Location in Ophiuchus

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

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