Roaming the Deep Sky #1
The Sword of Orion
By Don Clouse
The initial installment of this series focuses on a single field of view as opposed to a single object. The field surrounding the Great Orion Nebula, M42 (NGC1976), is star-studded and includes three other bright objects spanning a beautiful two degree field aligned north-south. This observation was done with a Celestron 80mm F/5 refractor. The observation was done at two powers. A Celestron 35mm Ultima eyepiece provided magnification of 11.4x and a field of view of nearly 4.5 degrees. A Televue, 15mm Panoptic provided 27x and a field of just over 2.5 degrees, comfortably encompassing the entire "Sword". The observation was done from an urban site (my back deck in the Highlands a few blocks from Bellarmine College) featuring a magnitude 4.5 sky, at best.
The first object on the north side of the field (or top of the Sword) is an open cluster, NGC1981. (Refer to the chart, which shows stars to tenth magnitude. The circle represents a 2.5 degree field of view.) It is listed with a diameter of 25’ and a magnitude of 4.2. At 11x, I counted eight stars. Moving south, two smaller patches of nebulosity, NGC1973 and 1975, were not visible. However, NGC1977, an open cluster with associated nebulosity, also magnitude 4.2, is easily visible. Its listed size is 40’x25’. I could see NGC1977’s three brightest stars at 11x – but no nebulosity. Next in line as we move down the Sword is M43 (a "detached ", smaller piece of the Orion Nebula) followed closely by M42, the Great Orion Nebula. This nebulosity contains the small open cluster called the "Trapezium". M42 is listed at magnitude 3.7 with a size of 90’x60’ although the dimmer outer areas are visible only in a larger telescope. At 11x, M42 was visible as a small, softly glowing area. At the end of the Sword is open cluster NGC1980 which also includes some nebulosity. It has a magnitude of 2.5 (!) and a diameter of 13’ and includes magnitude 2.8 Iota Orionis also known as Nairalsaif. At 11x I could see six stars but no nebulosity.
At 27x the entire Sword still fit easily within the 2.5 degree field. Each of the clusters (NGC1981, 1977, and 1980) showed a few more stars. Using averted vision, M42 began to show some detail in the bright central area while the Trapezium was just resolved into its four main stars and very, very, tiny indeed! Nearly the entire length of the Sword is involved in nebulosity with M42 easily being the brightest portion. I have to believe that the nebulosity associated with the clusters as well other patches (e.g., NGC1973 and 1975) require dark skies and very probably larger aperture telescopes – if they can be seen at all. However, I still look forward to toting my little refractor to a dark site to observe this starry, two-degree, panorama. Lots more stars will be visible. I just may try a filter too. Who knows? Maybe the nebulosity can be seen after all. In any event, with M42 in its midst, this is a truly lovely field – well worth the trek to a dark site on a cold winter night.
Visitors of This Page Since 2/27/02
