NGC 1978

NGC 1978 (also known as ESO 85-SC90) is an elliptical shaped globular cluster in the constellation Dorado. It is located within the Large Magellanic Cloud. It was discovered by James Dunlop on November 6, 1826.^[7] At an aperture of 50 arcseconds, its apparent V-band magnitude is 10.20, but at this wavelength, it has 0.16 magnitudes of interstellar extinction.^[4] It appears 3.9 arcminutes wide.^[8] NGC 1978 has a radial velocity of 293.1 ± 0.9 km/s.^[9]

NGC 1978
The globular cluster NGC 1978
Observation data (J2000 epoch)
Class	VI[1]
Constellation	Dorado
Right ascension	05h 28m 48s[2]
Declination	−66° 13′ 59″[2]
Distance	159,700 ly[3] (49,000 pc[3])
Apparent magnitude (V)	10.12[4]
Apparent dimensions (V)	10.7′ × 3.9′[3]
Physical characteristics
Mass	2×105[5] M☉
Metallicity	[Fe/H] = −0.38 ± 0.02 dex
	${\displaystyle {\begin{smallmatrix}\left[{\ce {M}}/{\ce {H}}\right]\end{smallmatrix}}}$ = 0.008[6] dex
Estimated age	1.9 ± 0.1 Gyr[6]
Other designations	ESO 85-SC90, KMHK 944
See also: Globular cluster, List of globular clusters

The northwest half of NGC 1978 is iron-rich and younger whereas the southeast part of the cluster has very little iron.^[9] NGC 1978 is also highly elliptical (ε ~ 0.30 ± 0.02),^[6] suggesting tidal action between it and the Large Magellanic Cloud.^[9] It is rich in pulsating asymptotic giant branch stars, often oxygen-rich or carbon-rich.^[5] NGC 1978 is about 2 billion years old. Its estimated mass is 1.36×10⁵ M_☉, and its total luminosity is 3.41×10⁵ L_☉, leading to a mass-to-luminosity ratio of 0.40 M_☉/L_☉.^[4] All else equal, older star clusters have higher mass-to-luminosity ratios; that is, they have lower luminosities for the same mass.^[4]