|Designation:||Dark Nebula Caldwell 99|
|Apparent size:||375 x 250 arc-min (that’s big! the Moon is 30 arc-min).|
|Diameter:||53 light years.|
|Distance:||490 light years.|
|Exposure:||Canon 60D, 50mm fixed lens, 1 x 15 seconds, f/2.5, ISO 3200.|
|Field of View:||26.6° x 17.7°|
|Orientation:||Up is 87.1° E of N.|
|# of stars:||Count them yourself! 🙂|
Looking like a hole in the Milky Way, the Coalsack is actually a huge dark nebula, which is neither a reflection nebula nor an emission nebula. It can be seen as a silhouette against the Milky Way star fields without optical aid in dark skies.
Probably the most prominent dark nebula in our skies, it is somewhat puzzling that – until the creation of the Caldwell Catalogue in 1995 – it had no identification number, not even an NGC listing – and is not even included in the Barnard List of 366 Dark Nebulae.
For goodness sake, the least they could do is add it as Barnard 367!
The Coalsack is too big to fit in the field of view of most telescopes. I took this single frame image four years ago with a DSLR on a tripod mount, probably with my Star Adventurer which has a motorised RA axis.
Prominent stars in the image include:
Top: Alpha Crucis (Acrux) and Beta Crucis (Mimosa) in Crux.
Bottom: the two Pointers, Alpha Centauri (Rigil Kentaurus) and Beta Centauri (Hadar) in Centaurus.
In retrospect, I probably should have made this object no 8 in my list of the Seven Best Southern Sky objects!