Sunday, October 29, 2006

Using M43 for calibration

Jeremy Perez's recent post of M42 & M43 at Belt of Venus is phenomenal.

Browsing through the blogs I regularly visit, I came across his sketch which stirred memories of a recent outing in dark sky. At one point in the evening, we were observing M45, particularly looking for Merope Nebula. Instead I saw, or claim to see, nebulae around at least three of the Pleiades. Others said it wasn't, passing it of as flare/glare in the eyepiece, eyepiece defects, bright star irradiation, etc. Each nebulous patch did not surround the stars equally. To me, it was unmistakable as a grayish white nebulosity that was very pronounced in a southerly direction.

Which brings me back to M42 & M43. Actually, it is M43 that is of interest. I use M43 as a benchmark to set my expectations when looking for other faint, low surface brightness nebula, for example like M78. (I can also use the far reaches of M42 to the west/southwest to calibrate my expectations.)

In Jeremy's sketch one can see M43 around the star northeast of M42, to the upper left and similarly with the photo on SEDS. My experience has been that this nebula is difficult and not as large. And oftentimes, M43 doesn't have enough punch to show in our urban skies or requires averted vision. When I detect it, M43 typically hugs the star and sometimes pulls away in the opposite direction of M42, shaped like a "comma".

So after the others said they did not see nebulosity around M45 the 18" scope was swung to Orion's Nebula. What good fortune because I was able to see the M43 and the far reaches of M42. And by the looks of M43, which was visible but not spectacularly brilliant, it affirmed my confidence of seeing the nebulosity. In fact when M42 came up no one mentioned M43. I asked one other if he saw M43 but he said he was uncertain. My notes don't indicate a comparative brightness between M43 & M45, which I could do next time.

With that said, I was led to believe that none of the observing party had seen M45 nebulosity before because no one stated it or remarked to the contrary that they had seen it. Hopefully a time will come when I get to see it and then have an experience to rely upon.