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Splitting Theta1,2 Orionis Naked-Eye in M42

Astrometry Binoculars Double Star DSO Moon Observing Report
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#1 SNH

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Posted 17 January 2022 - 11:20 PM

This evening I was out with my 130mm reflector watching the asteroid 1994 PC1 go zipping up through Fornax into Eridanus. At 7pm, the the Full Moon was 20° up in the east and 47° north of M42, which was 32° up. I have a younger friend who has been able to split the double star Theta1,2 ( θ1,2) Orionis. I, however, haven’t been able to do it under my Bortle Class 2 skies. The reason I always figured is because the Great Orion Nebula completely overpowers the two Thetas. So, with the Full Moon washing out the sky, my 10x50 binoculars showed M42 was merely a soft, faint glow around the two Thetas.

 

This was the moment I had been meaning to create (by using twilight or bright moonlight) for several years. I walked around to the west side of my house and was able to block the Moon with a chimney while still being able to see Orion. With the naked-eye, I could see three groups of light – one where the two Thetas are, one a bit north inside the currently invisible “Running Man” nebula, and two south inside the open cluster NGC 1980. With carefully study, the two Thetas was strongly elongated vertically and for moments I could split them.

 

Doing the math, I find that if all the member stars of θ1 Ori were at their brightest, it’s visual magnitude would be +4.64. But if all the member stars of θ1 Ori were at their faintest, it’s visual magnitude would be +4.98. That averages out to be about +4.8. And while θ2 Ori can be split easily with binoculars, that is not so with the naked-eye. So I get +4.7 when I combine +5.0 θ2 Ori A and +6.2 θ2 Ori B. In the 10x50 binoculars I did notice that +5.0 θ2 Ori A was fainter than +4.8 θ1 Ori (so my observation does match up with my math). Also, while the WDS Catalog says it is 134.4” between θ1 Ori C and θ2 Ori A, I am going to say that naked-eye they are more like 140” since each has fainter companions enhancing their glow “to the outside”.

 

Thus, in my book, I’m going to say that Theta1,2 ( θ1,2) Orionis is 140” apart and +4.8/+4.7 with the naked-eye. Amazing that I was able to split them considering my next closest was Epsilon1,21,2) Lyrae at 209.5”! What I am now wondering is how many more people might be able to split the two Thetas in more light-pollution? I'm not sure it would help any since you have to be able to see past magnitude +5.0 and yet have M42 pretty much as a ghost.

 

Scott H.

 

M42 Thetas.JPG


  • Mike B, timokarhula and Thomas Marshall like this

#2 Mike B

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Posted 16 March 2022 - 12:45 AM

I’ve recently been struck by the Theta 2 line-up in the near field of the Great Nebula & Trapezium viewed in my 6” Mak, and at deeper magnified (~150X) views I’m finding Theta 2 A appears to have a faint companion. Am I imagining this? I’ve scoped all over the web and can’t find an answer. It appears in similar fashion to the E star in the Trap relative to its Theta 1 primary as far as brightness & separation.

 

If anyone knows or can supply a link to this, I’d be most appreciative!

flowerred.gif Mike B


Edited by Mike B, 16 March 2022 - 12:46 AM.



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