When: throughout the night
What’s special: There are very few deep-sky sights that can equal, let alone surpass, the magnificence of a great globular cluster filling the field of view of a high-power eyepiece, with myriad sparking suns crammed together and all vying for attention. We are spoilt for choice at this time of the year, with many of these ancient star cities being well placed. Starring roles are played by Messier 13 and Messier 92 in Hercules, Messier 5 in Serpens, and last but definitely not least, Messier 3 in Canes Venatici, a truly top-rank globular cluster that can hold its own with all the aforementioned beauties.
Messier 3 (NGC 5272), which shines brightly at magnitude +5.9, is easily seen through 10 × 50 binoculars and is a stunning sight through a telescope. Thankfully, a large telescope isn’t required to get a really good view of it.
How to observe: Canes Venatici, the Hunting Dogs, lies well up in the east as darkness falls. Messier 3 is located in its extreme south-east, close to the boundaries with Boötes to the south-east and Coma Berenices to the south-west. Sweep with binoculars or a small telescope about six to seven degrees east of magnitude +4.2 beta (β) Comae Berenices. At mid-month, M3 can be observed for a profitable seven to eight hours, with it culminating at around 1am BST (00:00 UT) at an advantageous altitude of 67 degrees from London.
Messier 3’s individual stars at the outer edges its 19-arcminute form can start to be resolved through a 80–100mm (three-to four-inch) telescope at around 100×. Resolving a globular cluster’s individual stars at high powers is the main observing objective and provides spectacular views. A 200–250mm (eight-to ten-inch) telescope operating on a night of good seeing can reveal countless stars across M3, with the latter mining those deep at its core.
