Friday, March 15, 2013

Winter open clusters

The weather of the past few months has been unusually cloudy and rainy, with tornadoes hitting my city twice in one week during the Christmas holidays. But a few clear nights came along between the frequent storms of this winter, and naturally I made use of them. As of late I was concentrating on the open clusters of the constellations Canis Major and Puppis, two winter constellations that lie along the winter Milky Way. Here an amateur astronomer can find any kind of deep sky objects from galaxies to unusual stars.  Since I was observing from home, I concentrated mainly on open clusters. In Canis Major and Puppis you can find open clusters that range from those which are visible to the unaided eye to others which are faint blurs visible only in large telescopes.
NGC-2345 is a large scattered open cluster in Canis Major. Shining at a magnitude of 7.7 and with an apparent size of 12 arc minutes, NGC-2345 was easy to pick out from the background star fields. It's stars were rather faint, this spray of stars is an easy find in medium sized telescopes.

Larger and brighter NGC-2354 is less obvious amid the star clouds of Canis Major, even though it shines at magnitude 6.5 and has an apparent size of 20 arc-minutes. This star cluster lies in between Delta Canis Majoris and the bright open cluster NGC-2362. It's stars are more scattered, numerous and  fainter than the members of NGC-2345. They are arranged in chains that seem to enclose dark voids within the star cluster's apparent boundaries.
NGC-2374 is another Canis Major open cluster I had wanted to take a close look at, but it's apparent size of 19 arc-minutes and magnitude of 8 makes it appear quite faint through the telescope. There seems to be a five pointed star like concentration of stars in this object, which amid the countless background stars in the winter Milky Way made NGC-2374 an interesting sight. Since this object is two thirds the apparent size of the full moon, the star cluster occupies most of the field of view at 181X

NGC-2383 is just as bright as NGC-2354, but much more concentrated and rich with brighter individual stars. It stands up well to quite high magnifications and stands out well against the background star fields even when there's substantial light pollution.  Shining at an apparent magnitude of 6, NGC-2383 has an apparent size of 8 arc minutes, or a quarter of the width of the full moon.

NGC-2414 in Puppis is a small and rich open cluster with a prominent bright star in the center. Through my 10-inch it was easy to make out from my light polluted driveway at 149X. This star cluster is only 4 arc-minutes across and shines at magnitude 7.9, making it able to penetrate urban light pollution and stand out well against the background star clouds.

NGC-2423 lies just to the north of the bright open cluster M-47, and therefore is often overshadowed by it's brighter and larger neighbor. Shining at magnitude 6.7 with an apparent size of 19 arc-minutes, NGC-2423 boasts a large population of moderately bright and fainter stars.

NGC-2440 is a bright planetary nebula with a bi-polar inner region surrounded by an oval outer shell. It responds well to an O-III filter and the inner peanut shaped region is very evident. I was not able to see the central star due to the poor seeing. Around the bi-polar inner region there is a fainter outer shell that is faintly visible, with the whole nebula shining at a magnitude of 11. It's apparent size of 30 arc-seconds results in a high surface brightness, making this nebula visible to suburban stargazers.

NGC-2451 is a very bright open cluster easily through binoculars or a small telescope. In the center is a bright yellow-orange star surrounded by fainter blue-white and white stars. This star cluster is at least half again as big in apparent size as the full moon, with a total magnitude of 2.8. My 24mm Explore Scientific 82 degree eyepiece comfortably took in the entire star cluster through the 15-inch, which was set against a rich starry background. This object is one of the jewels of the southern skies that is nicely visible from the southern United States.

NGC-2489 resides in the northern reaches of Puppis about 8 degrees due east of the bright star Adhara, or Eta Canis Majoris. Shining with an apparent magnitude of 7.9 and an apparent size of 8 arc-minutes, this star cluster is a good object for a small telescope under favorable conditions. It seems to display a dark central void through the 15-inch from the driveway, even though long exposure photos show the area filled with stars too faint to see from there, even with a 15-inch. As open clusters go, it's fairly concentrated and rich with at least two dozen members.

NGC-2527 is a very large but rich open cluster that spans 22 arc-minutes of sky. It's overall magnitude of 6.5 is misleading because the star cluster is composed of a large number of 10th magnitude and fainter stars, making it somewhat of a ghost object hiding in plain sight. From my house it eluded detection through my smaller telescopes, but it showed up plainly through the 15-inch. From a dark area it would be a good object for a modest telescope.

Like it's nearby neighbor NGC-2451, the open cluster NGC-2546 is a very large object that takes up much of the field of view at low power through the 15-inch. Unlike that star cluster, NGC-2546 is made up of much fainter 9th to 12th magnitude stars that are arranged on several groups, nor is there a single bright star or lucida in the center. The whole cluster is some 41 arc-minutes across, bigger than the full moon. Shining at magnitude 6.5, it is visible to small telescopes and binoculars from darker locations, especially from the southern hemisphere.

NGC-2567 is another Puppis open cluster I paid a visit to. This object has a formation of stars that runs through the center as a wavy line. With an overall magnitude of 7.4 and an apparent size of 10 arc-minutes, NGC-2567 needed medium magnifications to reliably pick out from the background star clouds and Mobile's light pollution. Fairly rich with 11th magnitude and fainter stars, I located it with smaller telescopes from home with little difficulty.

Less than two degrees to the north lies NGC-2571, another open cluster that has a similar appearance at the same magnification. It's slightly brighter at 7th magnitude but the larger apparent size of 13 arc-minutes gives it a similar appearance to NGC-2567.

Normally I prefer to observe galaxies and nebulae, but inclement weather and other considerations ensured I was observing at home for most of the winter. I always wanted to get a closer look at these open clusters while they were still in a good position to observe. There's still a number of galaxies and nebulae in this area I would like to observe, but soon Puppis and Canis Major will be lost in the glare of the Sun, and numerous galaxies await my attention, as well as the now visible PANSTARRS comet. Soon I will be posting drawings of this icy visitor from deep space.

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