Weekly Binocular Objects
WBO 1: 2018 Week 5 (29th Jan) - Collinder 70 (Orion's Belt Cluster)
For the first object in this series, we’ll start off gently with a star cluster that’s both easy to find and perfectly suited to the wide field view of binoculars, yet often overlooked as an observing target.
Looking to the South at around 20:00 (GMT), many of you will be familiar with the majestic winter constellation of Orion (see chart in image 1), most easily identified by the three bright stars forming “Orion’s Belt”. From left to right, these three stars are called Alnitak, Alnilam and Mintaka, and are in fact part of a larger star cluster designated Collinder 70 (abbreviated Cr70).
Look at the belt and raise the binocular to your eyes, focusing to obtain sharp stars if necessary. You will see the three brightest belt stars spanning the view, but also many tens of other stars in the region (there are hundreds in the cluster). See if you can spot the unusual ‘loop’ of stars between Mintaka and Alnilam, which looks like a backwards question mark. Also have a look for the subtle difference in star colours in the cluster, which gives you a rough indication of their temperature (blue/white = hotter, orange/red = cooler).
Image 2 shows a simulated binocular view for 10x magnification binoculars (10x50, 10x42, etc.); the exact view will depend on your own binocular type/size and sky conditions.
With a bright moon high in the sky for the early part of the week (full moon Wed 31st Jan), the best time to observe this cluster is towards the end of the week when the moon will be very low in the East at around 20:00.
Orion contains many binocular delights, as we shall see next time when we investigate Orion’s sword…
(images courtesy of Stellarium - www.stellarium.org)
Image 1 - Location of Orion
Image 2 - Simulated Binocular View (10x42, etc.)