Splitting the double double

[Daz1974]

Evening all,

Just come in from a couple of hours observing and spent some time on Alberio then onto the double double in Lyra.

With my 130P, in light polluted stevenage with an 8mm BST and a 3x Tal I could clealry split both doubles.

I was pretty chuffed with that as I thought I would need a bigger scope so was wondering if it is that easy to split them and that i was getting over excited for nothing as its not too much of a big deal?

[carlc]

To be honest the best I have done is x125 but the SGL record is x48.

Having said that - yes you should be chuffed - the trick is now to try winding down the magnification to see 'how low can you go'? The more you practice the lower the mag you'll need.

[Daz1974]

From my calculations I make it I was viewing it at x243 so have a long way to go before getting anywhere near that!

With my scope and location I doubt that I could split them at any lower magnification but I'm happy enough actually being able to split them at all.

[carlc]

I don't think LP should make too much difference to doubles (but I may be wrong).

It could have been the seeing and transparency last night - I'm not far from you and there was a layer of high cloud.

I think you could do better than x243 - just keep going back every so often - spend time at the eyepiece each time and things will get better - everyone says 'seeing' is a skill that needs practice. Last time I had a go the seeing was patchy and as I spent time at the eyepiece the stars were split and then not and then split again. Nothing had changed except the atmosphere I just had to be patient and stand there for 15 minutes or so until I was sure I had split them and it wasn't imagination.

Also when you get depressed go look at the Struves (2470 and 2474) they're not far away - they're prettier and much easier to split - see Qualia's blog post http://stargazerslounge.com/blog/1218/entry-1246-lyras-doubles-doubles-a-view-from-a-city/ (sorry I'm a Qualia fanboy but they are useful posts).

[nightfisher]

I don't think LP should make too much difference to doubles (but I may be wrong).

It could have been the seeing and transparency last night - I'm not far from you and there was a layer of high cloud.

I think you could do better than x243 - just keep going back every so often - spend time at the eyepiece each time and things will get better - everyone says 'seeing' is a skill that needs practice. Last time I had a go the seeing was patchy and as I spent time at the eyepiece the stars were split and then not and then split again. Nothing had changed except the atmosphere I just had to be patient and stand there for 15 minutes or so until I was sure I had split them and it wasn't imagination.

Also when you get depressed go look at the Struves (2470 and 2474) they're not far away - they're prettier and much easier to split - see Qualia's blog post http://stargazerslou...ew-from-a-city/ (sorry I'm a Qualia fanboy but they are useful posts).

Qualia`s blog posts are very detailed and informative

[acey]

Evening all,

Just come in from a couple of hours observing and spent some time on Alberio then onto the double double in Lyra.

With my 130P, in light polluted stevenage with an 8mm BST and a 3x Tal I could clealry split both doubles.

I was pretty chuffed with that as I thought I would need a bigger scope so was wondering if it is that easy to split them and that i was getting over excited for nothing as its not too much of a big deal?

Congratulations on splitting them. Light pollution makes no difference, within reason (though daylight would count as light pollution bad enough to cause a problem!). Splitting the double-double relies on sufficient magnification for the observer's eye, which in turn relies on sufficiently good atmospheric conditions (steady seeing) and sufficiently good optics. "Splitting" can mean different things to different people: a star image is really a tiny pattern of concentric rings, not a pure point. With the usual criterion (Rayleigh's) the double-double can be split with a 70mm scope if the optics are of sufficient quality. With a more generous definition of split it's possible with 60mm. But if the seeing is poor then they may not be splittable.

Finding the lowest magnification at which they are splittable is an interesting problem. The separation of the stars in each pair is approximately 2.5arcseconds and the resolution of the human eye is about 1 arcminute at best, in which case a magnification as low as x24 might theoretically be possible. The SGL record of x48 that has been mentioned still sounds exceptionally good: the stars would have had an apparent separation of only about 2 arcminutes in the eyepiece.

Edit: from Wikipedia I find the figures 1.2 arcminutes for best eye resolution and 2.3 arcseconds for Epsilon2 separation, suggesting a lower limit of magnification of 1.2/(2.3/60) = x31.3.

Edit: One observer at a Cloudy Nights thread reports splitting at x30 (and can also see a gnat at 15 feet). This implies a resolution of his eye of 30 x (2.3/60) = 1.15 arcminute.

http://www.cloudynig...Number/3231888/

[alan potts]

SGL record is X48, wow. I thought I did very well to split them a X76 on the 190mm and my skys are very good indeed. Well done that person.

Alan.

[Daz1974]

Interesting stuff, thanks for the explanations. I'm off to Portugal in a couple of weeks staying in a tiny village in the middle of nowhere which is nice and dark. Taking a little celestron 76mm mini dob so will see how I get on with that trying on the same target(s)

[Ibbo!]

I can confirm a 60mm can split it x98 the other week

Steve

[Stu]

There's a thread called 'Double double.....Gotcha' around somewhere with some mute discussion on this which might be of interest.

I think I posted in there that I got it at x86 with a 66mm apo refractor. It's a really great double to observe, I never tire of seeing it

Stu

[Stu]

I of course mean 'more discussion', unable to edit the post for some reason

Stu

[nightfisher]

sounds like i should have a go at the double double, any tips on finding it

[carlc]

Had a go last night and couldn't split at 125 or 166 (and I can't go any higher with the current EPs).

As I said - very dependent on conditions.

That said I had an awful night last night all round - found diddly new and the neighbours were determined to stay up all night and shine lights all over the place.

[carlc]

sounds like i should have a go at the double double, any tips on finding it

Jules - I'm not good with this celestial coordinates stuff - I still tend to think in Earth coordinates - but it's very close to Vega.

The sky and telescope atlas doesn't show it as part of Lyra (in terms of the constellation lines) but it makes a triangle with Vega and Zeta Lyrae (another double).

This diagram helps to imagine it http://earthsky.org/...ble-double-star - the two primaries are easy to split - it's resolving 4 stars that's the challenge.

ETA: Lyra is high at the moment so expect to be kneeling if using a frac - I got muddy knees the other night. Must collimate the Dob....

[Moonshane]

hi Jules, it's very easy to find. point your finder centered on Vega (currently the brightest star directly overhead when it goes darkish) and there's an obvious pair of stars near the edge of the finder field towards north. this pair splits again with each 'star' becoming a pair. lovely to see. you cannot miss them. I presume you have seen the ring nebula? if Vega is the centre of a clock then the ring is at 5 o'clock and the double double is at 8 o'clock but much closer to Vega.

[chiltonstar]

I had another good look at the double-double three nights ago after reading this thread, ringing the changes with different EPs and a Barlow. I could definitely see the split at x100, just at x60, but not below that (5" Mak). Seeing was slightly better than average. Best split was at x190 with an 8mm EP (BST - new, I'm impressed!).

Chris

[nightfisher]

hi Jules, it's very easy to find. point your finder centered on Vega (currently the brightest star directly overhead when it goes darkish) and there's an obvious pair of stars near the edge of the finder field towards north. this pair splits again with each 'star' becoming a pair. lovely to see. you cannot miss them. I presume you have seen the ring nebula? if Vega is the centre of a clock then the ring is at 5 o'clock and the double double is at 8 o'clock but much closer to Vega.

Nice one shane, wish i had read this post before going to dark site last night, i would have found it for sure, i did find a couple of doubles, Alkor/Mizor and another i still have to look up

[Mr Spock]

The best view I had of this was many years ago on my long since departed OMC-140. With a Meade 6.4mm Plössl giving x313 in steady skies I had four perfect white airy discs - awesome sight

[Hex]

Its quite an easy split I find at 125X and onwards I seek it out most nights in the summer, but then I like double splitting.

[Josh Wilson]

I was able to split it last night at about 80x last night, but just barely. Seeing was about 2.5/5 so I'll try it again tonight given the projected 4/5 seeing forecast. BTW, record is 48x?!! Must've been a very large aperture under completely dark skies and amazing seeing. What telescope was it with?

[Merlin66]

It was with a 4" TV Genesis refractor, from the outer suburbs of Brussels on a good night!

TV 10.4 plossl (circa 1987)

[carlc]

It was with a 4" TV Genesis refractor, from the outer suburbs of Brussels on a good night!

TV 10.4 plossl (circa 1987)

Ah! That would help - quality of glass is very important in splitting doubles.

[John]

Ah! That would help - quality of glass is very important in splitting doubles.

I think tight doubles, especially unequal brightness ones, are a good general test of a scopes optics and state of collimation. Astronomy books used to include an index of test doubles for each scope aperture. I don't see that much these days.

Seeing conditions play a large part too of course so the inability to get a clean split on a particular night should not be blamed straightaway on the optics.

[carlc]

Oh absolutely John.

I have only ever managed to split the double double at 125x once and have not repeated that (with the same scope) since.

Practice does help as well (not that I'm getting much of that).

[nightfisher]

hi Jules, it's very easy to find. point your finder centered on Vega (currently the brightest star directly overhead when it goes darkish) and there's an obvious pair of stars near the edge of the finder field towards north. this pair splits again with each 'star' becoming a pair. lovely to see. you cannot miss them. I presume you have seen the ring nebula? if Vega is the centre of a clock then the ring is at 5 o'clock and the double double is at 8 o'clock but much closer to Vega.

trying it tonight i have Vega nicely overhead, just waiting for it to get a little darker