The Dimmest Constellation

Have a look towards the south between 10 and 11pm in the next few weeks and you will see some bright stars: Castor and Pollux in Gemini are fairly high, Proycon in Canis Minor is a bit lower and Sirius is blazing closer to the horizon. To me, these “winter stars” often appear bolder and brighter than the stars in summer.

But to the east of Castor and Pollux is a sparse patch of sky where Cancer the Crab, the dimmest constellation in the night sky, is positioned.

The Constellation Cancer is positioned towards the South between 10 and 11 pm PST during late February and early March from Vancouver.

The brightest star in Cancer  beta-Canceri  or Altarf, is only magnitude 3.5 so it is quite faint when viewed from a location with moderate or worse light-pollution with your naked eye. The other bright stars in Cancer are magnitude 3.9 and fainter. Nevertheless, it is worth getting out binoculars or a small telescope to observe two impressive star clusters that are hosted in Cancer.

The Beehive Cluster is also knows as the Praesepe Cluster and is designated as M65 or NCG 2632. It is one of the nearest clusters to our solar system at distance of 610 light years. It appears fairly large with an apparent diameter of about 1.1 degrees.  The classic Greek astronomer Plolemy described it as a “Nebulous mass in the breast of Cancer”.  It was one of the first clusters observed by Galileo through his telescope and he managed to spot about 40 stars within the cluster. There are about 50 star visible with amateur equipment but over 1000 stars have being identified as being a part of the cluster with high probability.

Image of the Beehive Cluster
The Beehive Cluster also known as M44. Image Credit: Bob Franke

M67 is a more compact cluster. It is much older than M44 with an estimated age of 4 billion years vs 600 million years old for M44. The cluster was first discovered before 1779 by the German astronomer, Johann Gottfried Koehler, but then re-discovered a year later by Charles Messier who added it as the 67th object to his list of non-comets.

Image of the M67 open start cluster
The Open Cluster M67. Image credit: Nigel Sharp, Mark Hanna/NOAO/AURA/NSF