Messier 47

Messier 47 (M47 or NGC 2422), also known as NGC 2478^[3] is an open cluster in the mildly southern constellation of Puppis. It was discovered by Giovanni Batista Hodierna before 1654 and in his then keynote work re-discovered by Charles Messier on 1771.^[a] It was also independently discovered by Caroline Herschel.

Messier 47
Open cluster Messier 47 in Puppis Credit: NOIRLab / NSF / AURA
Observation data (J2000.0 epoch)
Right ascension	07h 36.6m [1]
Declination	−14° 30′[1]
Distance	498 pc[1]
Apparent magnitude (V)	4.4[2]
Apparent dimensions (V)	30′[2]
Physical characteristics
Mass	453[1] M☉
Radius	10.61 pc[1]
Estimated age	78 million years
Other designations	NGC 2422, NGC 2478, Cr 152
Associations
See also: Open cluster, List of open clusters

There is no cluster in the position indicated by Messier, which he expressed in terms of its right ascension and declination with respect to the star 2 Puppis. However, if the signs (+ and −) he wrote are swapped, the position matches.^[4] Until this equivalency was found, M47 was considered a lost Messier Object. This identification as the same thing (ad idem) only came in 1959 with a realization by Canadian astronomer T. F. Morris.^[5]

M47 is centered about 1,600 light-years away and is about 78 million years old. The member stars have been measured down to about red dwarfs at apparent magnitude 19. There are around 500 members,^[1] the brightest being HD 60855, a magnitude 5.7 Be star. The cluster is dominated by hot class B main sequence and giant stars, but a noticeable colour contrast comes from its brightest red giants.^[5]

It about a degree from Messier 46, which is much older and much further away.^[5]

Gallery

• 
  Image of star cluster Messier 47 taken using the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile.

See also

• List of Messier objects