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Rasalhague (Alpha Ophiuchi, 55 Ophiuchi) Star Facts

Rasalhague Facts

  • Rasalhague is a giant star that can be located in the constellation of Ophiuchus. The description is based on the spectral class.
  • Rasalhague is a main star of the constellation outline.
  • Based on the spectral type (A5III) of the star, the star's colour is blue - white .
  • Rasalhague is the 56th brightest star in the night sky and is the brightest star in Ophiuchus 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.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 48.59 light years away from us. Distance

Rasalhague's Alternative Names

Alpha Ophiuchi (Alf Oph) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

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. The Gliese ID of the star is GL 681AB. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names In Arabic, it is known as Ra's al-Hawwa'.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 55 Ophiuchi. The Flamsteed name can be shortened to 55 Oph.

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+12 3252.

More details on objects' alternative names can be found at Star Names .

Location of Rasalhague

The location of the giant 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 Rasalhague, the location is 17h 34m 56.00 and +12° 33` 38.1 .

Radial Velocity and Proper Motion of Rasalhague

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 -221.57 ± 0.71 milliarcseconds/year towards the north and 108.07 ± 1.06 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 11.70000 km/s with an error of about 1.00 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.

Physical Properties of Rasalhague

Rasalhague Temperature and Colour

Based on the star's spectral type of A5III , Rasalhague's colour and type is blue - white giant star. The star's effective temperature is 8,225 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

Rasalhague 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 25.23 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Rasalhague Radius

Rasalhague estimated radius has been calculated as being 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. 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 2.7267097866566874691160577574. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

Rasalhague Iron Abundance

Rasalhague Iron Abundance is -0.16 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context. The value comes from the Hipparcos Extended Catalog.

Rasalhague Apparent and Absolute Magnitudes

Rasalhague 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 Rasalhague

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 69.84000 which gave the calculated distance to Rasalhague as 46.70 light years away from Earth or 14.32 parsecs. If you want that in miles, it is about 274,531,804,927,674.59, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 67.13000 which put Rasalhague 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.

Using the 2007 distance, the star is roughly 3,073,324.20 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 7,389.00 Parsecs or 24,100.21 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Travel Time to Rasalhague

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Walking48,146,315,500.78
Car120271,543,850.03
Airbus A38073644,273,453.81
Speed of Sound (Mach 1)767.26942,469,149.68
Concorde (Mach 2)1,534.5421,234,547.16
New Horizons Probe33,000987,432.18
Speed of Light670,616,629.0048.59

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 Rasalhague Facts and Figures

Visual Facts


Primary / Proper / Traditional NameRasalhague
Alternative NamesAlpha Ophiuchi, Alf Oph, Ra's al-Hawwa', HD 159561, HIP 86032, HR 6556, 55 Ophiuchi, 55 Oph, BD+12 3252, Gliese 681AB
Spectral TypeA5III
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeGiant Star
ColourBlue
GalaxyMilky Way
ConstellationOphiuchus
Absolute Magnitude 1.30 / 1.21
Visual / Apparent Magnitude2.08
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)17h 34m 56.00
Declination (Dec.)+12° 33` 38.1
Galactic Latitude22.56851824 degrees
Galactic Longitude35.89416014 degrees
1997 Distance from Earth69.84000 Parallax (milliarcseconds)
 46.70 Light Years
 14.32 Parsecs
2007 Distance from Earth67.13000 Parallax (milliarcseconds)
 48.59 Light Years
 14.90 Parsecs
 3,073,324.20 Astronomical Units
Galacto-Centric Distance24,100.21 Light Years / 7,389.00 Parsecs
Proper Motion Dec.-221.57000 ± 0.71000 milliarcseconds/year
Proper Motion RA.108.07000 ± 1.06000 milliarcseconds/year
B-V Index0.15
Radial Velocity11.70000 ± 1.00 km/s
Iron Abundance-0.1600 ± 9.99 Fe/H
Eccentricity0.22350
Semi-Major Axis8711.0000000
Stellar Luminosity (Lsun)25.2300000
Brightest in Night Sky56th

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)2.73
Effective Temperature8,084 Kelvin

Sources and Links


SIMBAD SourceLink

Location of Rasalhague in Ophiuchus


Rasalhague Location in Ophiuchus

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

Ophiuchus Main Stars


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