OBSERVER’S CHALLENGE* – January, 2023
by Glenn Chaple
NGC 1245 Open Cluster in Perseus (Magnitude 8.4, Size 2.9)
The 2nd magnitude star Mirfak (alpha [α) Persei is the centerpiece of the sprawling naked eye cluster Melotte 20. It dominates the field of the accompanying WIKI image that serves as the finder chart for this month’s Observer’s Challenge. But Mel 20 isn’t the Challenge object. It’s the open cluster NGC 1245, which appears as a tiny smudge in the lower right-hand corner of the image.
NGC 1245 was discovered by William Herschel on the night of December 11, 1786. He cataloged it as a Class VI object (Very compressed and rich clusters of stars) and described it as “A beautiful and rich cluster of small and large stars 7 or 8’ in diameter. The large stars are arranged in lines like interwoven letters.” Modern studies show that the cluster is home to some 200 stars, the brightest of which shine at 12th magnitude.
Owners of GoTo scopes can home in on NGC 1245 by punching in its 2000.0 coordinates, RA 3h14m48s and Dec +47o15’11”. For the star-hopper, NGC 1245 is a 3-degree trek southwest of Mirfak. I chose the latter method when I tackled NGC 1245 with a 10-inch f/5 reflecting telescope on the evening of December 13, 2022. A slight haze and resulting magnitude limit of 4.5 made for less-than-ideal conditions. At 141X, I was able to make out about a dozen cluster members. Averted vision hinted at a dozen or so more. There was no sign of the hazy mist that the fainter cluster members would have produced had skies been darker. The cluster was hardly identifiable in a 4.5-inch f/8 reflector, with just 4 stars visible.
NGC 1245 is located some 9800 light years away and is approximately 27 light years in diameter. It has an estimated age of one billion years, Compare that to Mel 20, which is similar in size but 16 times closer and cosmically young at an age of 50 to 70 million years.
*The purpose of the Observer’s Challenge is to encourage the pursuit of visual observing. It is open to anyone who is interested. If you’d like to contribute notes, drawings, or photographs, we’d be happy to include them in our monthly summary. Submit your observing notes, sketches, and/or images to Roger Ivester (email@example.com). To find out more about the Observer’s Challenge, log on to rogerivester.com/category/observers-challenge-reports-complete.
NGC 1245 Image
Mario Motta, MD. (ATMoB) “Taken with my 32 inch F6,5 telescope, R,G.G, and Lum filters, about 2 hours total imaging time, with ZWO ASI6200 camera. Processed in pixInsight using new BlurXtermintor plug in.