IC 2391

Primary identifier: IC 2391
Other identifiers: Omicron Velorum Cluster, VdB-H 42, ASA 031
Type: Open cluster
Magnitude: 2.5 V
Diameter: 50'

RA: 08h 40m
Dec: –53° 04'
Constellation: Vela
Charts: U2000 428, MSA 2:981, SA 25, Discover 04
Visibility: Nov-May

Historical observations: Lacaille

This open cluster was discovered by Lacaille and included in his 1755 catalogue as Class II No. 5. In his half-an-inch 8x telescope he saw it as a "small star group."

Modern observations: Phil Harrington

Harrington notes that this "beautiful open cluster .. can be seen with the unaided eye on a good evening. My 11x80 glasses show a large, coarse gathering of many bright stars, including several doubles. Its brightest sun, 3.6 mag Omicron Velorum, looks like a brilliant sapphire set among a glistening backdrop."

Contemporary observations

Observer: Auke Slotegraaf

Date: 1998 Apr 27/28
Location: Stellenbosch (Die Boord)
Instrument: 11x80 tripod-mounted binoculars

Sky conditions: Seeing average, transparency average, dew.

Description: Very sparse cluster near the False Cross, containing 6 very bright stars. There are absolutely no borders; it beautifully fills the 4.5° field of view with long chains of stragglers [ENE; W; N; NW]. The brightest stars congregate more to the north, and there is a slightly unequal double star east. Within a circle encompassing these 6 bright stars are 13 other smaller ones, down to magnitude 9.5

Date: 2006 Nov 18
Location: Stellenbosch (Die Boord)
Instrument: 11x80 tripod-mounted binoculars

Sky conditions: Seeing average, transparency mediocre.

Description: A very large, very bright coarse cluster, just under 2° NNW of Delta Velorum. The most prominent star lies on the northern 'edge' of the grouping (HD 74195, V=3.6); on the eastern 'side' is a wide double star, slightly unequal in magnitude (V=4.9 & 5.5).

The boundaries of the cluster are arbitrary, but it contains at least five bright stars and as many much fainter stars. The cluster is about 25 arcmin across.

A star, which I labelled 'A' on a field sketch, appears reddish. Reducing the observations identifies this star as HR 3448 (HD 74196) with a B-V = -0.14, which is not red at all!

Observer: Constant Volschenk

Date: 2007 April 20, 22:55 SAST
Location: Ezemvelo Nature Reserve (25°42'S 28°57'E)
Instrument: Orion SkyQuest XT 10 IntelliScope, 40mm (30x) eyepiece

Sky conditions: Transparency: Partly Clear; Seeing: Mostly Stable

Description: Could not see with naked eye, but clearly visible in 9 x 50mm finder scope. Cluster is spread over wide field of view, 40mm eyepiece seems to be too a high magnification (???) There seems to be no stars in the centre of the cluster.