Sky Object of the Month – January 2018

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Sky Object of the Month – January 2018

(Courtesy LVAS Observer’s Challenge*)

NGC 1624 – Cluster/Nebula in Perseus (Mag. 10.4; Size 3.0’)


            If you like two-for-one bargains, you’ll appreciate this month’s LVAS Observer’s Challenge. On December 28, 1790, William Herschel’s all-sky survey brought him to“6 or 7 small stars, with faint nebulosity between them, of considerable extent, and of an irregular figure.” He duly catalogued it as H V-49 – his 49th Class V (very large nebulae) object. What Herschel had discovered was a small open star cluster embedded in an emission nebula.

            NGC 1624 is located 5 degrees east of magnitude 4.3 Lambda (λ) Persei in the far northeastern corner of Perseus. If your scope is equipped with Go-to technology, dial in the coordinates RA 04h40m25.4s, Dec +50°26’49”, and you’re on your way. If you prefer star-hopping, the finder chart below will help you plot a path from Lambda. A third method, described by Sky and Telescope’s late “Deep Sky Wonders” columnist Walter Scott Houston, might be worth a try, as long as you’re the patient sort. Scotty’s “sky-drift” method involves training your scope on a bright star located due west of the target and letting the earth’s rotation bring it into view. The rule is to wait 4 minutes for every degree of sky drift. In the case of NGC 1624, train your scope on Lambda and relax with a cup of hot chocolate for 20 minutes (actually, I’d start looking after 16).

The visibility of NGC 1624 is open to debate. One observer recommends a minimum aperture of 6 inches under dark skies. Yet current “Deep Sky Wonders” columnist Sue French writes, “Through my 105mm scope at 28X, it’s an obvious little fuzzlet centered on one faint star. A magnification of 127X unveils five faint stars caught in a filmy net about 4’ across.” Also debatable is this cluster/nebula’s visual magnitude. Some sources suggest a magnitude of 11.8, but this may refer to the brightest star in the cluster. The fact that Sue French was able to capture NGC 1624 in a 105mm scope might suggest another published visual magnitude of 10.4. An O-III filter will enhance the visibility of the nebula.

NGC is a young cluster with an estimated age of less than 4 million years. It lies 20,000 light years away, give or take a few thousand.

Glenn Chaple for the LVAS



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