| Open
Cluster with Nebula
aka Collinder 68, Stock 9, OCL 441 RA: 05h31m24.8s Dec: +34°15'12" (Auriga) Integrated Visual Magnitude: 10.1 Angular Diameter: 3.0' Minimum requirements to detect: 6-inch under dark skies |
NGC 1931 is a tiny little cluster of stars embedded in nebulosity found about a degree to the west of the open cluster M36. At the heart of the NGC 1931 cluster lies a tiny version of the famous Trapezium in M42; four stars that make a rough trapezoid.
This is a small object, so be sure to try as much magnification as the conditions will bear on it. In smaller scopes or at low powers it will appear as a fuzzy star. More magnification will reveal a fairly bright, round fuzzy knot of nebulosity. OIII and H-Beta filters have little effect on the nebula.
Brian Skiff gathered some
information regarding the trapezium stars, which I have reproduced below.
The multiple star system that forms the "little trapezium" is ADS 4112
(BD+34 1074).
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The A, B, and C stars are easy to see but the E component is a little more difficult. At least an 8-inch scope will be required to see it. The D component is even more difficult, requiring a very large aperture.
When I observed NGC 1931 in my 18-inch f/4.5 I immediately noticed the nebula as a bright knot at 97x. I was surprised at how bright it appeared. The best view came at 430x, where the little trapezium became very obvious.
The field in an 8-inch f/6
at 50x. North is down and east is to the right.
| Millennium
Star Atlas Vol I Chart 113
Sky Atlas 2000 Chart 5 Uranometria 2000 Vol I Chart 97 Herald-Bobroff Astroatlas B-05 C-22 |
