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Arcturus, Alpha Bootis, 16 Bootis, HD124897, HIP69673, HR5340

Arcturus (Alpha Bootis) is a orange to red giant star that can be located in the constellation of Bootes. Arcturus is the 5th 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.

Alpha Bootis 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 Gliese GL541. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Ref : Star Names.

Arcturus has alternative name(s), NSV 06603.

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.

Location of Arcturus

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

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.

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 70.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of Arcturus

Arcturus has a spectral type of K2IIIp. This means the star is a orange to red giant star. The star is 7396.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24123.0409222400000000s. 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. 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.

Arcturus Facts

Alternative Names

Traditional/Proper NameArcturus
Flamsteed Name16 Bootis
Flamsteed Short Name16 Boo
Short NameNSV 06603
Bayer DesignationAlpha Bootis
Hipparcos Library I.D.69673
Yale Bright Star Catalogue (HR) Id5340
Bonner DurchmusterungBD+19 2777
Gliese ID541
Henry Draper Designation124897

Visual Facts

Star Typegiant star
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.)+19d 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 Revised 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
Spectral TypeK2IIIp
Brightest in Night Sky5th
Colour(K) Orange to Red

Variable Star Details

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

Estimated Facts

Luminosity (x the Sun)70.0000000
Calculated Effective Temperature4,439 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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

Location of Arcturus in Bootes

Arcturus (Alpha Bootis) Location in Bootes

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

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