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Arcturus, Alpha Boötis, 16 Boötis, HD124897, HIP69673, HR5340

Arcturus (Alpha Bootis) Location in Bootes

Arcturus (Alpha Bootis) is a orange to red giant star that can be located in the constellation of Bootes. The description is based on the spectral class. Arcturus is a main star of the constellation.

Arcturus is the 4th brightest star in the night sky and is the brightest star in Bootes 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.

Arcturus is a massive star, it is many times bigger than our own the Sun. It is orange in colour meaning that its temperature based on the Hertzsprung-Russell diagram, it is between 4,000 to 5,250 Kelvin, hot enough to fry an egg. It is not as hot as the Sun which has a rough temperature of about 5,300 to 6,000 k.

Arcturus is the fourth brightest star in the sky, after -1.44 magnitude Sirius, -0.62 Magnitude Canopus and -0.27 Magnitude Alpha Centauri also known as Rigil Kentaurus. Even though Sirius is brighter than Arcturus, Arcturus is further away from our solar system.

No Extrasolar Planets (Exoplanets) have been discovered orbiting round this planet but its not to say that that they're aren't or weren't any. The star has held a position in science fiction for orbiting planets with life forms, for instance, Arcturans have been mentioned in Star Trek, where the aliens come from the fourth planet orbiting the star.

Arcturus's Alternative Names

Alpha Bootis (Alf Boo) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR5340. HIP69673 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD124897. The Gliese ID of the star is GL 541. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Arcturus has alternative name(s) :- , NSV 06603.

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 16 Bootis with it shortened to 16 Boo.

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+19 2777.

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

Location of Arcturus

The location of the 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 star is compared to the celestial equator and is expressed in degrees. For Arcturus, the location is 14h 15m 40.35 and +19° 11` 14.2 .

Radial Velocity and Proper Motion of Arcturus

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 -2,000.06 ± 0.35 miliarcseconds/year towards the north and -1,093.39 ± 0.54 miliarcseconds/year east if we saw them in the horizon.

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -5.24 km/s with an error of about 0.09 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.

Arcturus 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 206.84 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 Arcturus

Arcturus has a spectral type of K2IIIp. This means the star is a orange to red giant star. The star is 7,396.00 Parsecs from the Galactic Centre or terms of Light Years is 24,123.04 s. The star has a B-V Colour Index of 1.23 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,439 Kelvin.

Arcturus Radius has been calculated as being 18.21 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 12,671,282.80.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 18.21. 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 -0.50 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Arcturus Apparent and Absolute Magnitudes

Arcturus has an apparent magnitude of -0.05 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 -0.31 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.31. 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 Arcturus

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 88.85 which gave the calculated distance to Arcturus as 36.71 light years away from Earth or 11.25 parsecs. It would take a spaceship travelling at the speed of light, 36.71 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 88.83 which put Arcturus at a distance of 36.72 light years or 11.26 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 7,396.00 Parsecs or 24,123.04 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*. Arcturus brightness ranges from a magnitude of 0.140 to a magnitude of 0.093 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.0 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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Arcturus Facts

Visual Facts


Primary / Proper / Traditional NameArcturus
Alternative NamesAlpha Bootis, Alf Boo, HD 124897, HIP 69673, HR 5340, 16 Bootis, 16 Boo, BD+19 2777, Gliese 541, NSV 06603
Spectral TypeK2IIIp
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeGiant Star
Colour orange to red
GalaxyMilky Way
ConstellationBootes
Absolute Magnitude -0.31 / -0.31
Visual / Apparent Magnitude-0.05
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)14h 15m 40.35
Declination (Dec.)+19° 11` 14.2
Galactic Latitude69.11 degrees
Galactic Longitude15.07 degrees
1997 Distance from Earth88.85 Parallax (milliarcseconds)
 36.71 Light Years
 11.25 Parsecs
2007 Distance from Earth88.83 Parallax (milliarcseconds)
 36.72 Light Years
 11.26 Parsecs
Galacto-Centric Distance24,123.04 Light Years / 7,396.00 Parsecs
Proper Motion Dec.-2000.06 ± 0.35 milliarcseconds/year
Proper Motion RA.-1093.39 ± 0.54 milliarcseconds/year
B-V Index1.23
Radial Velocity-5.24 ± 0.09 km/s
Iron Abundance-0.50 ± 9.99 Fe/H
Eccentricity0.75
Semi-Major Axis2848.00
Stellar Luminosity (Lsun)206.84
Brightest in Night Sky4th

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Mean Variability Period in Days0.043
Variable Magnitude Range (Brighter - Dimmer)0.093 - 0.140

Estimated Facts


Calculated Effective Temperature4,439 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
124897+19 2777.0A0.20000-1093.00000-1999.00000K2Orange
B3.50000-1093.00000-1999.000001991

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