Constellation – Hercules
Right Ascension : 16h 41m 41.24s
Declination: +36°27′ 35.5”
Apparent Magnitude +5.8
Messier 13, M13, is one of the showcase deep sky objects in the Northern Hemisphere night time sky. For many who can’t see Omega Centauri, M13 is the most spectacular globular, although M22 in Sagittarius is considered by many its equal.
Discovered by Edmond Halley in 1714, this globular cluster was catalogued by Charles Messier on June 1, 1764 in his famous list of fuzzy objects that were not comets.
As shown in the image, there are dark lanes of globular cluster M13 known as “the propeller” (above and to the left of center in the image of M13)l. This image also shows the distant galaxy IC 4617 to the upper right of the cluster, which lies at a distance of 500 million light-years compared to M13’s distance of about 25,000 light years. A Cosmic Duet!
The question is how many of you have visually or photographically seen the propeller? Or better yet, how many of you knew of its existence?
This little-known feature of M13 is a challenge to view visually. I had seen it through my old C-11 Celestron before I sold it. It’s visible in my new 9.25” Celestron SCT through a 10mm eyepiece at 250x. I have heard of observers visually seeing the propeller through telescopes with apertures as small as 6”. A clear, low humidity, transparent night helps. Averted vision is needed to spot this feature, especially through single digit (in inches) aperture optics. High power in the range of 250x to 300x is the order of the day.
Astro-imagers should have success imaging the M13 propeller, but I have not seen any images using an 80mm aperture or smaller. That doesn’t mean it can’t be done with an 80mm, it just that I haven’t seen a published example.
So good luck viewing the Propeller!