Roaming the Deep Sky #8
NGC1245
By Don Clouse
NGC1245 is a lovely, 8.4 magnitude, open (or galactic) cluster in Perseus. Perseus is, perhaps, my favorite constellation to roam by naked eye with its long, curving chains of stars. NGC1245 is located near the beginning of one of these chains. Occupying the hub of this system of apparent star chains, is Alpha Persei, or Mirphak (the address for the home page of this wonderful web site by James Kaler is http://www.astro.uiuc.edu/~ekaler/sow/sow.html). Mirphak is located about 590 light years away. In addition to being the brightest star in Perseus, it is the brightest member of the very large naked eye open cluster, Melotte 20. This cluster extends about 2.5 degrees to the southeast of Mirphak and contains at least six other naked eye stars. What I’ll call the western curve, begins at Mirphak and curves to the south, to Algol and beyond. On this chain, the next star to the south of Mirphak is the magnitude 5.0 star, Kappa Persei. Between Mirphak and Kappa Persei, a bit closer to Kappa, is NGC1245. So, that’s where NGC1245 is located on the sky. Where it is located in the galaxy is, yes, another paragraph.
NGC1245 is located about 7,500 light years away in the Perseus Spiral Arm of our Milky Way Galaxy. The entire stretch of the Perseus Arm from the vicinity of M52 in western Cassiopeia to the Double Cluster in Perseus is continuous. It is studded with young open clusters and a number of dark molecular clouds that are still actively forming stars. However, between the Double Cluster and the Crab Nebula (M1) there are very few of the young open clusters and nebulae which usually line spiral arms. This gap in the Perseus Arm is where NGC1245 resides.
In a moderate sized telescope, this cluster reveals itself as a rich sprinkling of numerous minute points. My best look at this object (so far) was with my 8" Celestron SCT. In October, 1998 at Wyandotte Woods in southern Indiana, I used a 15mm, wide-field eyepiece, yielding 135 power with a 0.5 degree field of view. With direct vision, I could see about twenty scattered stars. With averted vision, perhaps three time as many faint pinpoints jumped into view. All these scattered, tiny, stars overlay the faint haze created by the unresolved cluster members. Observing this cluster again in November, 2001 at Curby, I estimated NGC1245’s size at 7’x4’ elongated east/west.
NGC1245 is listed as having a diameter of 10’ and 200 stars. The brightest of these are magnitude 12.5 stars. A good 4 inch scope (100mm), on a good night, may be able to resolve a few cluster members, but most likely will show a faint, unresolved haze. To resolve any cluster members, you’ll likely need at least 5 inches (125mm) of aperture. A 5" telescope should be capable of reaching 13th magnitude. More aperture, should pull in even more stars. I saw perhaps 60 stars in my 8" (200mm) telescope, which should show stars to 14th magnitude on a dark, steady night. A 12" (300mm) scope should pull in an especially spectacular view, showing stars down to about 15th magnitude.
The chart shows the location of NGC1245 between Mirphak (Alpha Persei) and Kappa Persei. Stars to 11th magnitude are shown. A typical 8x50 finder scope shows stars to the 11th magnitude. The chart is 9.7 degrees by 6.1 degrees in size. Mirphak and Kappa Persei are about 5.5 degrees apart. Enjoy.
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