Gamma Crucis

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**Gamma Crucis**
Observation data Epoch J2000
Constellation	Crux
Right ascension	12h 31m 9.9s
Declination	-57° 06' 45"
Apparent magnitude (V)	1.59
Spectral Characteristics
Spectral type	M4 III
U-B color index	1.77
B-V color index	1.60
Variable type	Semi-regular
Astrometry
Radial velocity (R_v)	+20.6 km/s
Proper motion (μ)	RA: 27.94 mas/yr Dec.: -264.33 mas/yr
Parallax (π)	37.09 ± 0.67 mas
Distance	88 ± 2 ly (27 ± 0.5 pc)
Absolute magnitude (M_V)	-0.56
Physical Characteristics
Mass	3 M_☉
Radius	113 R_☉
Luminosity	1,500 L_☉
Temperature	3,400 K
Metallicity	?
Rotation	?
Age	? years
Other designations
Gacrux, Gl 470, HR 4763, CD -56°4504, CP(D)-56 5272, HD 108903, LTT 4752, SAO 240019, FK5 468, HIP 61084.

Gacrux (γ Cru / γ Crucis / Gamma Crucis) is the third brightest star in constellation Crux (the Southern Cross) and one of the brightest stars in the nighttime sky. It is known as 十字架一 (the First Star of the Cross) in Chinese.

Since Gamma Crucis is at roughly −60° declination, it is only visible south of the Tropic of Cancer and therefore didn't receive an ancient traditional name; "Gacrux" is simply a combination of the "Ga" in Gamma plus Crux.

Gamma Crucis is a binary star, 88 light years distant from Earth. The main star possesses an apparent magnitude of +1.6 and belongs to the spectral classification M4 III. The +6.4 magnitude companion star (spectral classification A3) is in an angle of 25" with a position angle of 128 degrees of the main star, and can be observed with binoculars. The colour of Gamma Crucis is bright red.

This star has evolved out of the main sequence to become a red giant star, and may be passing out of the Helium-burning stage. It is also semi-variable with a period of about 90 days. The atmosphere is contaminated with barium, which are likely due to neutron emission from a companion that has since become an unseen white dwarf.