Thursday, January 19, 2017

Is that a Nebula?

In October of 2014, when I moved to China, my hope was to catch more DSOs and complete the Messier list. All that I had then was a little more than 30 Messiers that I have seen from Bogota and my 15x70 Celestron Skymaster binoculars. Upon arriving, the list started to grow faster. During the first 7 months I added to the list my firsty galaxies (other than M31), some more globular clusters and a few open clusters. Later, I had completed 75% of the whole list, but truly with the binos the list contained only smudges, fuzzy cottonish balls and blurry like stellar objects.  

I often like to compare binocular vs telescope views to show what magnification can do for one and this entry is one of those. This time the turn is for M46, a like nebular object in binoculars with a few stars inside it.  In fact, Caroline Hershel decribed it in 1783 like this: “1 deg S following the nebula near the 2nd Navis [Puppis; M47], a Nebula the figure is done by memory”. If I did not know it was an open cluster I could think it was a nebula region like the type of Lagoon or Orion Nebula.  

In middle of the very starry wide FOV, one can discern M47, a bright cluster at 2 o’ clock in the sketch. Right diagonal to it there is M46, a nebulous area with few resolvable stars.

Last december, I decided to apply more magnification to M46 and apart from resolving plenty of the individual stars in the cluster, I found a treasure among the stars: NGC 2438, a planetary nebula superimposed on the stellar cluster. With only 37.5x, but with averted vision, it was possible to see a circular and fuzzy smudge. With 100x it lost some of its surface brightness and looked like a ghosty and almost shapeless patch. In the sketch, it can be seen to the right of the cluster and it looks like a circular and dim fuzz. 

M46 has a an estimated population of about 500 stars with 150 of the stars between magnitude 10th-13th. With direct vision I could see about 30 of those stars and much more with averted vision. Unfortunately, while using averted vision I got lost inside the cluster and decided it was time to finish the sketch.

And finally, here is the original sketch with some additional information about this observation

Clear skies,


Edited by: Jennifer Steinberg (editor in chief)


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