Universe Guide

Gacrux (Gamma Crucis) Star Facts

Gacrux Facts

  • Gacrux is a eruptive giant star that can be located in the constellation of Crux. The description is based on the spectral class.
  • Gacrux is a main star of the constellation outline.
  • Based on the spectral type (M4III) of the star, the star's colour is red .
  • Gacrux is the 25th brightest star in the night sky and the 4th brightest star in Crux 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.
  • Gacrux has a radius that is 84.00 times bigger than the Suns. Radius
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 88.56 light years away from us. Distance

Gacrux's Alternative Names

Gamma Crucis (Gam Cru) 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 HR4763. HIP61084 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD108903. The Gliese ID of the star is GL 470. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Gacrux has alternative name(s) :- , NSV 05672.

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

Location of Gacrux

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 Gacrux, the location is 12h 31m 09.93 and -57° 06` 45.2 .

Radial Velocity and Proper Motion of Gacrux

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 -265.08 ± 0.11 milliarcseconds/year towards the north and 28.23 ± 0.18 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 21.00000 km/s with an error of about 0.10 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 Gacrux

Gacrux Temperature and Colour

Based on the star's spectral type of M4III , Gacrux's colour and type is red giant star. The star's effective temperature is 3,385 Kelvin which is cooler than our own Sun's effective Temperature which is 5,777 Kelvin

Gacrux Radius

Gacrux Radius has been calculated as being 84.00 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 58,447,200.00.km. If you need the diameter of the star, you just need to multiple the radius by 2.

Gacrux Apparent and Absolute Magnitudes

Gacrux has an apparent magnitude of 1.59 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 -0.56 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.58. 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 Gacrux

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 37.09000 which gave the calculated distance to Gacrux as 87.94 light years away from Earth or 26.96 parsecs. If you want that in miles, it is about 516,966,315,317,766.66, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 36.83000 which put Gacrux at a distance of 88.56 light years or 27.15 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 5,600,050.47 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 7,386.00 Parsecs or 24,090.42 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 Gacrux

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)
Airbus A38073680,692,674.82
Speed of Sound (Mach 1)767.26977,404,155.08
Concorde (Mach 2)1,534.5438,702,027.10
New Horizons Probe33,0001,799,691.17
Speed of Light670,616,629.0088.56

Variable Type of Gacrux

The star is a eruptive Irregular variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. Gacrux brightness ranges from a magnitude of 1.677 to a magnitude of 1.592 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 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 Gacrux Facts and Figures

Visual Facts

Primary / Proper / Traditional NameGacrux
Alternative NamesGamma Crucis, Gam Cru, HD 108903, HIP 61084, HR 4763, Gliese 470, NSV 05672
Spectral TypeM4III
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeGiant Star
GalaxyMilky Way
Absolute Magnitude -0.56 / -0.58
Visual / Apparent Magnitude1.59
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)12h 31m 09.93
Declination (Dec.)-57° 06` 45.2
Galactic Latitude5.65039095 degrees
Galactic Longitude300.16908459 degrees
1997 Distance from Earth37.09000 Parallax (milliarcseconds)
 87.94 Light Years
 26.96 Parsecs
2007 Distance from Earth36.83000 Parallax (milliarcseconds)
 88.56 Light Years
 27.15 Parsecs
 5,600,050.47 Astronomical Units
Galacto-Centric Distance24,090.42 Light Years / 7,386.00 Parsecs
Proper Motion Dec.-265.08000 ± 0.11000 milliarcseconds/year
Proper Motion RA.28.23000 ± 0.18000 milliarcseconds/year
B-V Index1.6
Radial Velocity21.00000 ± 0.10 km/s
Semi-Major Axis7334.0000000
Brightest in Night Sky25th

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassEruptive
Variable Star TypeIrregular
Mean Variability Period in Days0.074
Variable Magnitude Range (Brighter - Dimmer)1.592 - 1.677

Estimated Calculated Facts

Radius (x the Sun)84.00 (84.00 - 84.00)
Effective Temperature3,779 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
108903-56 5272.4A1.6000029.00000-267.00000M4Red
108925-56 5274.4B6.700003.00000-6.00000A2White1919
-56 5276.4C9.500001879

Location of Gacrux in Crux

Gacrux Location in Crux

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

Crux Main Stars

Comments and Questions

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Izabela SmigulskiMonday, 25th September 2017 2:57:40 PM
How can I find out which are the closest stars to Gacrux? Or is this not possible from our position e.g. dwarfs close to Gacrux may not be visible to the viewers from our position.
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