The year moves on, and so does the night sky. In the Northern Hemisphere, summer's deep sky objects start to make an appearance in the late evenings -- favourite bright stars such as Vega in Lyra and Arcturus in Boötes make a return from the east, and with them some stunning Messier deep sky objects. A couple of hours' observing in late April revealed some real stunners, including M13, and M92. Much lower down, I should have been able to see M3 in the constellation Canes Venatici, and M57 (the Ring Nebula) in the constellation of Lyra, but pretty bad light pollution from local industry towards my eastern horizon severely restricts observing low down deep sky objects with low surface brightness, such as planetary nebulae, galaxies and star clusters.
I always tend to use a 26mm or 20mm eyepiece initially when viewing deep sky objects, following successfully lining them up in my finderscope. Sometimes, as in the case of M81 (Bode's Nebula) and M82 (the Cigar Galaxy) in Ursa Major, the smaller eyepiece and wider angular field of view allows for some attractive framings of deep sky objects together. When it is time for closer inspection, I increase the magnification with my x2 Celestron Barlow lens. In my location, with moderate light pollution and no filter, most deep sky objects, being so faint, really don't bear greater magnification with a 200mm aperture reflector, except of course, bright star clusters and objects such as M42, the Orion Nebula.
So what my bagging of these two superb globular clusters, both of which looked stunning at x80 magnification? Both are globular clusters. M92 alternatively known as NGC 6341 was discovered in 1777 by Johann Elert Bode, and has an apparent magnitude of +6.4 making it one of the more conspicuous globular clusters. Charles Messier independently rediscovered it and catalogued it on March 18, 1781. It lies 26,700 light years distant in our galaxy's halo, like M13 in the constellation of Hercules.
M92 is visible to the naked eye under very good conditions and a showpiece through either a telescope or binoculars. It has a mass of approximately 330,000 suns, and has an angular size of 14 arc minutes, astonishingly it is closing in on the central regions of the Milky Way at a staggeringt 112 km/sec!
So much or M92, what about the superb 'Great globular cluster in Hercules', otherwise known as M13 or NGC6205? It's at a similar distance of about 25,100 light years, has an apparent magnitude of +5.8, and has an angular size of 20 arc minutes. It was discovered by Edmond Halley in 1714, and is one of the best known globulars in the of the Northern celestial hemisphere. M13 contains several 100,000 stars, and in 1974 was a target for one of the first radio messages addressed to possible extra-terrestrial intelligent races, sent by the large radio telescope at Arecibo.
Both M13 and M92 are gems in the northern night sky, and summer's the time to start making the most of them!
