OBSERVER’S CHALLENGE* - MAY, 2021
by Glenn Chaple
Messier 3 – Globular Cluster in Canes Venatici (Mag: 6.2, Size: 18”)
After a steady diet of faint Observer’s Challenges in recent months, we can relax our eyes with the bright globular cluster Messier 3. At a magnitude of 6.2, it ranks among the 10 brightest of the roughly 250 globular clusters that inhabit our galaxy. It can be glimpsed with the unaided eye from remote dark-sky locations and is easily spotted in binoculars from suburban areas.
M3 was discovered by Charles Messier on May 3, 1764. To him, it appeared as a nebula without stars. Twenty years later, William Herschel resolved it into a stellar mass.
Finding M3 is one of its biggest challenges. It lies in a star-poor region of the constellation Canes Venatici. Owners of GoTo scopes can dial in its coordinates - RA 13h42.2m, DEC +28°22.6’. Star-hoppers will find M3 by aiming their telescopes towards an area roughly midway between Arcturus and Cor Caroli (alpha [α] Canum Venaticorum) and then slowly scanning the area with low power until a hazy circular patch of light comes into view.
A switch to high power brings M3 to life, especially in scopes with apertures of 6 to 8 inches and above. Smaller instruments at high magnification will hint at its stellar nature. Amateur Telescope Makers of Boston President Rich Nugent reports a grainy appearance when viewing M3 with a 5-inch refractor. Through a 4-inch rich-field scope at high magnification, I suspected a hint of graininess.
M3 lies about 33,000 light years away. Its estimated half million stars occupy a sphere 180 light years across.
Image by Mario Motta (ATMoB) Taken with 32-inch telescope, SBIG STL1001E Camera, RGB filters. North is up.