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Arcturus (Alpha Boötis, 16 Boötis) Star Facts

Arcturus Facts

  • Arcturus is a 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 outline.
  • Based on the spectral type (K2IIIp) of the star, the star's colour is orange to red .
  • 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 has a radius that is 25.40 times bigger than the Suns. Radius
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 36.72 light years away from us. Distance

Information on Arcturus

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 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 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 named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 16 Bootis. The Flamsteed name can be 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 objects' alternative names can be found at Star Names .

Location of Arcturus

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 Arcturus, the location is 14h 15m 40.35 and +19° 11` 14.2 .

Radial Velocity and Proper Motion of Arcturus

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 -2,000.06 ± 0.35 milliarcseconds/year towards the north and -1,093.39 ± 0.54 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 -5.24000 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.

Physical Properties of Arcturus

Arcturus Colour and Temperature

Based on the star's spectral type of K2IIIp , Arcturus's colour and type is orange to red giant star. The star's effective temperature is 4,336 Kelvin which is cooler than our own Sun's effective Temperature which is 5,777 Kelvin

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.

Arcturus Radius

Arcturus Radius has been calculated as being 25.40 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 17,673,320.00.km. If you need the diameter of the star, you just need to multiple the radius by 2.

Arcturus Iron Abundance

Arcturus 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. The value comes from the Hipparcos Extended Catalog.

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 88.85000 which gave the calculated distance to Arcturus as 36.71 light years away from Earth or 11.25 parsecs. If you want that in miles, it is about 215,804,337,449,570.32, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 88.83000 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.

Using the 2007 distance, the star is roughly 2,322,525.53 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 7,396.00 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*.

Travel Time to Arcturus

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)
Walking46,156,260,654.22
Car120205,208,688.47
Airbus A38073633,457,938.34
Speed of Sound (Mach 1)767.26932,094,405.76
Concorde (Mach 2)1,534.5416,047,181.97
New Horizons Probe33,000746,213.41
Speed of Light670,616,629.0036.72
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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Additional Arcturus Facts and Figures

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
ColourOrange 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 Latitude69.11106419 degrees
Galactic Longitude15.06558209 degrees
1997 Distance from Earth88.85000 Parallax (milliarcseconds)
 36.71 Light Years
 11.25 Parsecs
2007 Distance from Earth88.83000 Parallax (milliarcseconds)
 36.72 Light Years
 11.26 Parsecs
 2,322,525.53 Astronomical Units
Galacto-Centric Distance24,123.04 Light Years / 7,396.00 Parsecs
Proper Motion Dec.-2000.06000 ± 0.35000 milliarcseconds/year
Proper Motion RA.-1093.39000 ± 0.54000 milliarcseconds/year
B-V Index1.23
Radial Velocity-5.24000 ± 0.09 km/s
Iron Abundance-0.5000 ± 9.99 Fe/H
Eccentricity0.75200
Semi-Major Axis2848.0000000
Stellar Luminosity (Lsun)206.8400000
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 Calculated Facts


Radius (x the Sun)25.40
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

Location of Arcturus in Bootes


Arcturus Location in Bootes

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

Bootes Main Stars


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