Orion Doubles

[AndyWB]

So on the 30th of last month I took my 250px out for, well, a bit of a test run as much as anything else. I was still in town, so didn't think it'd offer much more on DSOs than the 130p (though the Orion nebula was even more spectacular). This led me to think "I know, why don't a try a few doubles, test the optics?" Turn Left at Orion has a few pages of doubles, so I started working through them.

• Rigel was easy to split, once I'd spotted the B component hidden in the diffraction spikes at x150.
• Eta-Orionis split - just but clearly - at x150.
• Mintaka was a wide split at low magnification
• Next I realised I'd forgotten to really look at the Trapezium, so I checked it. A-E were easy, but I just couldn't make out the F component.
• Iota Orionis and Struves 747 and 745 were easy at x150. Iota Ori showed A-C nicely
• Sigma Orionis and Struve 761 were easily split again at x150. Sigma Ori showed AB, C, D and E. C was dim
• 32-Ori I couldn't split. Might have looked a little elongated.
• Meissa was a pretty straight forward split
• 52-Ori I couldn't split. Might have looked a little elongated.
• Alnitak again seemed an easy split, despite the glare.

What struck me about this was that 32-Ori and 52-Ori are supposed to have separations of 1.1" and 1.2" - and didn't split (though I didn't try ridiculous magnifications - I only went to x240). Yet Eta-Ori (1.8") wasn't very hard at all. I know it's a 50% wider separation, but still, I was surprised by such a marked difference.

And Theta Ori A-E is about the same as C-F (around 5" separation) yet I could see E, but not F. Weird.

And I thought Rigel was a tough split, but in the 250px it seemed … not too hard.

I'm not sure I have a point, I just found it interesting. I did also wonder if a 250px wasn't overkill for splitting bright doubles, though it's resolution did seem much better than my 130p

[John]

Thats a nice list of targets. Unequal brightness will make close doubles tougher to split and C Trapezium is brighter than A thus making F (which lies close to C) that much harder. I'm sure you will do it another time - I can see both quite regularly with my ED120 although getting the "right" magnification seems to be important with these objects - not too much and not to little. You need to experiment a bit !

Eta can be a tough one so that was a nice one to get. It's possible that 1.5 arc seconds or so was around the limit for the particular night you were observing, hence making 32 and 52 just a bit too much for that session.

You can press more magnification on doubles - I find 300x is quite useful even with my ED120 refractor. 

[AndyWB]

Yeah, I did wonder about if it was just the magnitude difference on Theta1 ORI A-C, and C was visibly brighter. It was just strange that one was so clear, and the other not. I'll try experimenting as you say if I ever see another clear sky!

And yes, I was chuffed about Eta I figured as you say that maybe 1.5ish arcseconds might have been the limit, but I suppose I'd expected 32 and 52 ORI to show as definitely elongated. Ah well, next time I'll try x300 as you suggest; I'm still getting a feel for just how far you can push with doubles, and it does seem to vary a lot between different nights.

You know, I hadn't really taken on board that Orion was full of nice doubles - I guess mostly people talk about the Orion nebula. I also got Beta-MON, which was a cute triple, though I still think the constellation Monceros doesn't actually exist...

[NGC 1502]

Nice report.

Double & multiple stars are a favourite target of mine.

They show up very well through the light pollution of Southend in Essex.

I get as much pleasure hunting down double stars from home, as I do chasing the faint stuff from a dark site.

I use the Cambridge Double Star Atlas, but loads of online info out there.

Regards, Ed.

[Special K]

Good report and your list can come in handy! This is the second instance I've heard lately of the wealth of doubles in Orion. Worth a good look when this rain passes through! There is a definite satisfaction in splitting doubles, and I don't do enough of it. Ed, that Cambridge atlas sounds tempting as it also serves as a more detailed edition than the Cambridge Star Atlas I've got.

[AndyWB]

I've been looking for the Double Star atlas, but it seems out of print or something.

[NGC 1502]

I've been looking for the Double Star atlas, but it seems out of print or something.

Online double star database here http://www.saguaroastro.org/content/downloads.htm scroll down to find it.

Haven't fully checked that out, but most info from them is good.

Regards, Ed.