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Eta Crucis, HD105211, HIP59072, HR4616

Eta Crucis (Eta Crucis) Location in Crux

Eta Crucis is a blue to white giant star that can be located in the constellation of Crux. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it. The star has an estimated age of 1.60 Billion of Years but could be as young as 1.40 to 1.70 according to Hipparcos.

Eta Crucis's Alternative Names

Eta Crucis (Eta Cru) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR4616. HIP59072 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD105211. The Gliese ID of the star is GL 455.2. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

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

Location of Eta Crucis

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 Eta Crucis, the location is 12h 06m 52.85 and -64° 36` 49.1 .

Proper Motion of Eta Crucis

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 -37.02 ± 0.09 miliarcseconds/year towards the north and 33.88 ± 0.12 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 us is 10.40000 km/s with an error of about 0.40 km/s .

Eta Crucis 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 7.17 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, Age) of Eta Crucis

Eta Crucis has a spectral type of F2III. This means the star is a blue to white giant star. The star is 7,391.00 Parsecs from the Galactic Centre or terms of Light Years is 24,106.73 s. The star has a B-V Colour Index of 0.35 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,967 Kelvin.

Eta Crucis Radius has been calculated as being 1.87 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,303,977.20.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 1.88. 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 -0.10 with an error value of 0.15 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 1.60 Billion years old but could be between 1.40 and 1.70 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Eta Crucis Apparent and Absolute Magnitudes

Eta Crucis has an apparent magnitude of 4.14 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 2.67 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.66. 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 Eta Crucis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 50.79 which gave the calculated distance to Eta Crucis as 64.22 light years away from Earth or 19.69 parsecs. It would take a spaceship travelling at the speed of light, 64.22 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 50.62 which put Eta Crucis at a distance of 64.43 light years or 19.76 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 7,391.00 Parsecs or 24,106.73 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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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Eta Crucis Facts

Visual Facts

Primary / Proper / Traditional NameEta Crucis
Alternative NamesEta Cru, HD 105211, HIP 59072, HR 4616, Gliese 455.2
Spectral TypeF2III
Multiple Star SystemYes
Star TypeGiant Star
Colour blue to white
GalaxyMilky Way
Age1.60 Billion Years Old
Age Range1.40 - 1.70 Billion Years Old
Absolute Magnitude2.67 / 2.66
Visual / Apparent Magnitude4.14
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)12h 06m 52.85
Declination (Dec.)-64° 36` 49.1
Galactic Latitude-2.15 degrees
Galactic Longitude298.18 degrees
1997 Distance from Earth50.79 Parallax (milliarcseconds)
 64.22 Light Years
 19.69 Parsecs
2007 Distance from Earth50.62 Parallax (milliarcseconds)
 64.43 Light Years
 19.76 Parsecs
Galacto-Centric Distance24,106.73 Light Years / 7,391.00 Parsecs
Proper Motion Dec.-37.02 ± 0.09 milliarcseconds/year
Proper Motion RA.33.88 ± 0.12 milliarcseconds/year
B-V Index0.35
Radial Velocity10.40 ± 0.40 km/s
Iron Abundance-0.10 ± 0.15 Fe/H
Semi-Major Axis7970.00
Stellar Luminosity (Lsun)7.17

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Estimated Facts

Calculated Effective Temperature6,967 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
105211-63 2145.4A4.3000038.00000-33.00000F0Yellow/White

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