Roaming the Deep Sky #16
The Sculptor Galaxy, NGC 253
By Don Clouse
NGC 253 is a large, bright, spiral galaxy in the constellation Sculptor. It is sometimes called the Sculptor Galaxy or the Silver Coin Galaxy. This type Sc galaxy is tucked away nearly 7.5 degrees south of Beta Ceti (Diphda, a class K0 III giant, 96 light years away) at a declination of about minus 25. Even at this southerly declination, it shows considerable detail in a modest sized telescope.
At the Twin Lakes Star Party in October 1999, I managed to get a pretty good look at this galaxy in my 8" Celestron SCT (f/10, 2030mm focal length). At 58x (with a 51’ true field of view), it appeared quite large and fairly bright. I estimated its size at 25’x6’ (catalogued size is 30’x7’), oriented NE/SW. The central 8’ was bright, but no real core or nucleus was evident. However, within this extended central bright area, two or three brighter areas were discernable especially with averted vision. At 135x, in addition to filling nearly the entire half-degree field of view, there were hints of darker areas in the central region. It really looked pretty darn cool.
NCG 253’s location is shown in our MegaStar chart (click here for chart). Four other NGC galaxies (55, 247, 300, and 7793) are also shown. These galaxies, along with several fainter ones, make up the Sculptor Galaxy Group. This group is also know as the South Polar Group since NGC 253 is located only two degrees northwest of the south galactic pole. This assemblage is about 10 million light years distant. However, NGC 253 itself may be only 8 million light years away. At some 60,000 to 70,000 light years in diameter (compared to our Milky Way Galaxy’s 100,000 light year diameter), the Sculptor Galaxy is a sizable class Sc spiral galaxy (Sc = small core, loosely wound arms). It is very nearly edge-on being only slightly tilted to our line of sight. Photographs (click on "list" in the "Galaxies" line then on "AAT 23") show very dusty spiral arms and numerous HII regions indicating the recent formation of many large, bright star clusters.
The best time to view NGC 253 is when it is near due south. (This, of course, is because when an object is due south it is as high in the sky as it will get thus minimizing atmospheric extinction. Objects lower in the sky are dimmed by a light path that must punch through more atmosphere. The higher an object is the less atmospheric extinction, or magnitude loss, it suffers.) NGC 253 is in the close vicinity of due south at about 1am in mid to late September, 11pm in mid to late October and around 9pm in mid to late November. For mid December viewing, you’ll want to observe NGC 253 just after the end of astronomical twilight. This occurs at around 7pm at which time the galaxy will be very close to due south. Do I detect a pattern here? Well, yes. It’s "merely" the combined effect of our position on the planet, our planet’s rotation about its axis, and the planet’s orbit around our star. Very predictable. And isn’t it wonderful that these factors have all been combined and represented in an elegant instrument called the planisphere?
Digressions aside, The Sculptor Galaxy is highly recommended. I can’t believe it took me four years to get around to viewing this galaxy. But now that I’ve seen it, I’m certain I’ll be revisiting it often. Take a look for yourself the next time you get the chance. How much detail can you see?
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