Monthly
Messier Star-Hops; October #1
By
Art Russell
By now it should be apparent that our long wait through the summer has finally paid off. Our patience has already been rewarded with cooler evenings and some of the clearest nights since last spring. I just hope that next summer the wait isn’t as long or as arduous.
This month’s star-hops will be south of the Zenith (which is located directly overhead) and therefore easier to observe than those we located last month. We’ll start off near the “Great Square of Pegasus” and journey to the specatular globular cluster M15. From there we’ll then journey to the constellation Aquarius. There we’ll find the globular cluster M2, the open cluster M73 and its close companion, the globular cluster M72. The stars used for pointing the way in these star-hops are not as bright as those you may have become accustomed to previously. However, if you can observe from dark skies with little light pollution to obscure them, even these dimmer pointing stars will be sufficient to locate this month’s deep sky quarry. But once again, the key is dark skies! You can’t do these star-hops from downtown Atlanta. Pack up your telescope, charts and eyepieces, and escape to the country to chase down this month’s deep sky objects.
Star-Hop
#1; M15, NGC 7078
Star-Hop #2; M2, NGC 7089
Star-Hop #3; M73, NGC 6994 and M72,
NGC 6981
Star-Hop #1; M15, NGC 7078. M15 is a spectacular globular cluster and the closest rival of M13 in the skies north of the celestial equator. Located in the western most reaches of the constellation Pegasus, M15 makes an interesting contrast to the other globular clusters still visible at this time of year. Locating M15 will also orient us for our subsequent star-hops this evening. So where to start? Looking directly overhead on the evening of 15 October at 10PM, you’ll find the zenith as portrayed by our map of star-hops. From there, you will find the “Great Square of Pegasus” located a little more than 20 degrees, or the distance between the tip of your thumb and little finger when you hold your hand at arms length and outstretched against the sky, to the east-southeast. You may also be able to find the “Great Square of Pegasus” from the constellation Cygnus. From Cygnus, the “Great Square of Pegasus” is located a little more than 40 degrees or two hand spans, also to the east-southeast. The sometimes easily identified “Great Square of Pegasus” is notable by the relative lack of stars within its boundaries. Once we’ve located the “Great Square of Pegasus” we have completed the toughest part of locating M15. Locate Alpha (a) Pegasi at the southwest corner of the “Great Square of Pegasus.” From there, extend an imaginary line about 15 degrees, or the distance spanned by your fist against the sky, past Xi (x) and Zeta (z) Pegasi, to the star Theta (q) Pegasi. From Theta (q) Pegasi, extend an imaginary line to the northwest past the star Epsilon (e) Pegasi. Past Epsilon (e) Pegasi, extend the line a little less than 4 degrees or slightly less than your forefinger and index finger held together at arms lenght. M15 will be just slightly north of this line. In binoculars and small telescopes, M15 appears as a small circular nebulous object without any hint of individual stars. Medium telescopes will resolve many stars and reveal the globular cluster to be nonsymetrical in shape. Larger telescopes will resolve many more stars and also suggest the appearance of lanes within the globular cluster itself. What does your telescope show?
M15 @ 250X
Star-Hop #2; M2, NGC 7089. Just like the star-hop to M15, we use Alpha (a) Pegasi in the “Great Square of Pegasus” as our starting point to star-hop to M2. As before, we extend an imaginary line about 15 degrees to the star Theta (q) Pegasi. Extending this line past Theta (q) Pegasi for another 11 degrees, or just a bit more than than the distance spanned by your fist at arm’s length will bring you to M2. There are also two alternative ways to locate M2. A second alternative is to locate the stars Alpha (a) and Beta (b) Aquarii in the constellation Aquarius. M2 forms the apex of a right triangle located to the west of Alpha (a) Aquarii and north of Beta (b) Aquarii. In binoculars and small telescopes M2 appears as a small circular nebulous object with a sharply concentrated nucleus, but without resolving any individual stars. Moderate telescopes will resolve many of the outer stars of M2, but most of the stars in the center of the cluster remain unresolved.
Star-Hop #3; M73, NGC 6994 and M72, NGC 6981. The open cluster M73 is only a little more than a degree, or the width spanned by your little finger against the sky, away from the globular cluster M72. Since they are so close, we can use the same star-hop for M73 and M72. Although M73 and M72 lie in the constellation Aquarius, we will need two pointing stars in the constellation Capricornus to help us locate them. Starting in the Aquarius, locate the star Epsilon (e) Aquari. Epsilon (e) Aquari forms the northern apex of an imaginary equilateral triangle formed with our other pointing stars. Beta (b) Capriocorni, the southwestern apex of the triangle is located about 10 degrees, the distance spanned by your fist at arm’s length, to the southwest from Epsilon (e) Aquari. Theta (q) Capricorni forms the southeastern apex and final corner of our triangle. Theta (q) Capricorni is located a little less than 10 degrees to the southeast of Epsilon (e) Aquari and just a little bit more than 10 degrees east-southeast of Beta (b) Capriocorni. We’ll find M72 and M73 a little bit past the mid point along an imaginary line from Theta (q) Capricorni to Epsilon (e) Aquari. At this piont we’ll find M73 just to the east of our imaginary line and M72 just to the west of our imaginary line. Both of these deep sky objects are reserved for telescopes or perhaps BIG binoculars, so be sure to observe them from a dark site. In a medium sized telescope M73 appears as only a few dim stars and M72 appears as a dim circular nebulous object.