Theta Orionis

The Trapezium

Multiple Star system
Constellation: Orion
RA: 5h 35m 17s
Dec: -5 23′ 27″

The Trapezium is the most famous multiple star system in the entire night sky. Located at the very heart of M42, the Orion Nebula, it is one of the youngest star clusters known.

The other weekend I was out observing with our club. I was using my trusty C9.25 and it was a clear and steady night. One of our club members (Bob Pitt) had his 10mm Ethos eyepiece with him and he plopped it into my scope to see how well the 9.25 could handle a good eyepiece. And away we went on a wild ride through the night sky. After tackling a few 9th and 10th magnitude doubles and the like we ended up on M42.

I centered the ‘trap’ in the eyepiece and ‘POP’ there were 4 bright stars staring back at me. What a view, 4 beautiful stars wrapped in a nebulous cloud. I settled into a comfortable viewing position and let my eye relax and then I saw the (for the first time clearly with the C9.25) E and F stars as faint specks of light in the eyepiece!

He and I were very excited that we had them and called some others over to the scope to share the view. After couching the guys on what to look for and how to look for them it hit me that not many people go beyond the 4 principle stars in the trapezium.There are actually 10 stars in Theta Orionius (as illustrated below)

A-D are readily apparent in a 3.5-6 inch scope. In an 8-10 inch scope A-F are very easy to view given the proper conditions. Normally the cluster looks like the illustration below

Personally I have never tried to get G-I (which are hard to get I have heard) but at the next star party I plan to attack these stars with the clubs 20 inch Obsession and see how far I get!

These are stars that vary in magnitude from 14.5 to 15.5, which are on the far outer edge of what I can get with the 9.25, but I think that the Obsession 20 can handle the calling. I really want to try and split H1/H2 which have been measured at 1.6 arch seconds and should be easily done on a still night with a 20 inch telescope.

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