Sky Object of the Month – July 2018

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Sky Object of the Month – July 2018
(Courtesy LVAS Observer’s Challenge*)
Messier 4 – Globular Cluster in Scorpius (Mag. 5.8; Size 26’)

For the second straight month, the Las Vegas Astronomical Society’s Observer’s Challenge is a Messier object – this time, the globular cluster M4 in Scorpius. M4 is bright and easy to find (it’s visible in binoculars just 1.3 degrees west of Antares), so where is the challenge? For starters, M4 is rather sparse as globular clusters go. What is the smallest aperture that resolves its stars? Secondly, William Herschel reported “a ridge of stars running through the middle from south preceding to north following.” This spindle of 10th to 12th magnitude stars appears in the Mario Motta image below. Can you see it visually, and with what aperture and magnifying power? Herschel also noted that these stars were red. Can you detect any color?
At a distance of approximately 7200 light years, M4 is one of the nearest globular clusters. It was discovered by the Swiss astronomer Jean-Philippe Loys de Chéseaux in 1746 and was catalogued by Messier 18 years later.

Glenn Chaple for the LVAS

Mario Motta, MD

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