Splitting doubles - questions

[Roger Fairhurst]

Although very much a newbie I have been able to see quite a lot so far with my modest equipment especially clusters and galaxies.

Because beginners on SGL are not treated like dim wits when posing basic questions I would like to put the following questions about double stars to the old, not so old, wise and not so wise who frequent this site and who, to the detriment of wife, kids, work and pets, take the time to help us "first formers" on the slippery slope towards "total awareness".

I have often read on SGL about "splitting doubles" and presume by this we mean being able to observe (with scope or bins) the two distinct stars which constitute a double star system.

1. Presumably all (or nearly all) of these stars are not visible as doubles to the naked eye and need optical assistance in order to "split them" - am I right?!

2. I know that Sirius is a double star - and is often refered to as a binary star - so do the terms binary and double mean the same thing in this context?

3. I would like to have a crack at splitting a couple of doubles especially Sirius (when it's high enough for me to target), the double double and a few others which are not too difficult to locate and split - which other doubles would come into this last category?

4. What else in the way of basic knowledge should I be looking to gain with respect to doubles to make finding and splitting with modest equipment enjoyable?

Kind regards

Roger

[Peter Drew]

Hello Roger.

1) "Double" stars fall into two main categories, optical, two stars in the line of sight appearing close together and physical, two stars revolving round their common centre of gravity.

2)3) Sirius is a double star but its companion is very faint by comparison and is a very difficult object to observe.

4) There are lists if double stars available elsewhere. As a rule of thumb double stars can be separated if their separation is not less than 4.56 seconds of arc divided by the aperture in inches. This is for two stars of around magnitude 6. Variation of magnitudes between the two stars very much increases the difficulty in splitting them. In general, splitting close double stars requires the best seeing and high magnifications. Hope this helps for starters. 

[ronin]

The confusion of the terms is owing to the fact that 2 stars can be a "double" because they appear close to each other by being on the same line of sight but at different distances along that line, these are sometimes called optical doubles.

The other which is what I suspect you are thinking of is when 2 stars are close physically and are gravitationally bound to one another.

The Sirius double is a binary system, the stars are gravitationally bound.

Not sure what precise terms are used.

The following site is a list of nicely coloure double stars, binary or optical I am not sure:

DalawareAS

May as well have some that are interesting coloure.

If you put "coloured double stars" into google one of the first is a list of 200, well that it what it says.

Another option is The Astro League, and go through the observing programs they have:

AstroLeague

There is a double star program there which may provide a guide.

Simple double is Mizar/Alcor, middle "star" in the handle of The Plough, binoculars will separate them, so that's a start.

[Stu]

Although very much a newbie I have been able to see quite a lot so far with my modest equipment especially clusters and galaxies.

Because beginners on SGL are not treated like dim wits when posing basic questions I would like to put the following questions about double stars to the old, not so old, wise and not so wise who frequent this site and who, to the detriment of wife, kids, work and pets, take the time to help us "first formers" on the slippery slope towards "total awareness".

I have often read on SGL about "splitting doubles" and presume by this we mean being able to observe (with scope or bins) the two distinct stars which constitute a double star system.

1. Presumably all (or nearly all) of these stars are not visible as doubles to the naked eye and need optical assistance in order to "split them" - am I right?!

2. I know that Sirius is a double star - and is often refered to as a binary star - so do the terms binary and double mean the same thing in this context?

3. I would like to have a crack at splitting a couple of doubles especially Sirius (when it's high enough for me to target), the double double and a few others which are not too difficult to locate and split - which other doubles would come into this last category?

4. What else in the way of basic knowledge should I be looking to gain with respect to doubles to make finding and splitting with modest equipment enjoyable?

Kind regards

Roger

Ok, let's have a go at this.

1). Doubles can be naked eye, binocular, telescopic or spectroscopic. This entirely depends upon their separation. If you take Alcor and Mizar as an example, they are a naked eye double. Mizar itself is a close binocular or easy telescopic double to split so they show as a three star system; Mizar A, Mizar B and Alcor. I believe some, if not all of these are spectroscopic binaries too which means they are too close to separate with a telescope, but by analyzing the light from them you can detect the Doppler shift showing that it is actually two stars orbiting each other.

2). Double star and binary star mean the same thing. Binary just means having two components.

3). Sirius is very tricky for a number of reasons. The components are very different brightnesses so the brighter Sirius A component tends to drown out the smaller B component. The separation is not that small so, it is the glare that is the main issue. It is also not very high when viewed from the UK, so you are looking through slot of turbulent air to see them. Rigel is a similar, but easier double with two unequal components, and I guess Polaris aswell, but less so.

The double double is often higher in the sky, so the challenge is to get good seeing conditions, a scope which is well cooled and collimated and enough magnification to split them. A good refractor will do it under x100, my best is x69 and there are folks in here who have split it at x49. Over x150 you should definitely split them given the right conditions.

4). I guess the main things to look for are to understand the separation and brightnesses of the stars, and to try to split the tricky ones. Izar is a good one to try, although not well positioned currently. The other lovely thing to look for is different coloured doubles which can be beautiful. Almach and Alberio are two 'classics' which are well worth a look. Quite easy to find and split, but with lovely different coloured components. There are also multiple star systems out there. The trapezium in M42 and Sigma Orionis are two that spring to mind. The trapezium will easily show four stars, but trying to find the E and F components is a challenge of scope, conditions and just the right magnification.

There are plenty of double star lists around if you search for them. The Struve list is one but others will post up more I'm sure.

Enjoy!

Cheers,

Stu

[Stu]

Just to add, the separation of the Double Double is around 0.06 degrees for the two main components and they are visible as a double star through binoculars. Each part of this can then be split to show all four components, and the separation of each if the sub doubles is around 2.4 arc seconds. Below this sort of level gets pretty tricky and certainly below 1 arc second is extremely challenging, requiring high quality optics, well collimated and and cooled, and large enough to have sufficient resolution to split them.

Stu

[Roger Fairhurst]

WOW!!!

Well I asked for it - as the actress said to the bishop!

Thanks guys you've given me plenty to ponder over and bone up on while the weather is so uncooperative!

I guess as with most things, the more you realise just how little you know!! At least I'm not yet quite old enough for this to worry me.

kind regards

Roger

[Roger Fairhurst]

I guess as with most things, the more you realise just how little you know!!

Should of course read:

"I guess as with most things, the more you learn the more you realise just how little you know!! "

When I reach 250 posts I'll be able to edit instead of correcting with a separate post.

Kind regards

Roger

[wxsatuser]

Not only doubles but mulitiples, love splitting them photograpically.

Couple I posted in the doubles imaging section, it can be addictive.

Alcyone multiple

and Polaris

[Astro Imp]

Here's a good start for double stars:- http://users.compaqnet.be/doublestars/

[ronin]

If you REALLY want to scare yourself off of ever looking for/at doubles try this:

WDSC   :grin: :grin:

Also before it disappears try for the double double in Lyra.

[Roger Fairhurst]

and Polaris

See, that's what I mean about the more you learn... the less you know !!!

I know how to find Polaris and I've located it quite a few times without any problem but never thought of it as a double star and therefore only ever saw it as something to be viewed through the polar scope for alignment purposes or for fun.

It is now down on a list of objects to "crack" together with a number of other suggestions on this thread.

Once again fellers - thanks a bunch.

... and nice photos wxsatuser but there's NO WAY I'm gonna get involved with astrophotography myself - that is on my list of things to AVOID doing at all costs!!!

Kind regards

Roger

 

[F15Rules]

Observing double stars can become really addictive...whether to see different colours, large or small differences in brightness, close doubles, multiple stars etc etc. It's fascinating. I've always favoured long focal length scopes for doubles. They don't have to be that big, one of my favourite double star splitting scopes is an older 76.2mm F16.5 achromat..but because it IS such a long focal length, it has a large depth of focus, or putting it another way, a longer range of sharp focus than you would find in a shorter focal length scope. 

For example, I see that you have a Skywatcher 150mm F5. I have a Celestron 150mm F8 and the older F16.5 mentioned above. Although the aperture of your scope and my big refractor are the same, the F8 longer Focal length will mean it is easier to resolve and bring to clear fine focus at high powers double and multiple stars in my scope. And, within it's smaller light gathering limits, the F16.5 will make it easier again to get that fine focus at high power - which is often the difference between suspecting a split and being sure of seeing a clean split.

Modern shorter focus scopes often have a crayford dual speed focuser which helps to achieve a fine focus. Another must for high magnification splitting of doubles is a stable mount. You can't overmount a scope and the more rigid it is, the better the views at high power.

A good challenge for your SW 150 F5 will be Delta Cygni..it's well within the grasp of your scope (my 4" ED100 splits it nicely at high power), but it will be interesting to see if your short focal length scope will allow you a high enough magnification to see it clearly. 

Have fun!

Dave

[wxsatuser]

... and nice photos wxsatuser but there's NO WAY I'm gonna get involved with astrophotography myself - that is on my list of things to AVOID doing at all costs!!!

Kind regards

Roger

 

I know what you mean.

it's got me and I cannot get away.

[AndyWB]

FWIW, I find this blog quite useful - well researched, with excellent descriptions - http://bestdoubles.wordpress.com/

As well as doubles, there are also multi-star systems too. While you're having a go at the Double-Double (Epsilon Lyrae), check out Beta Lyrae, which might be a multiple system (reports seem to vary - it may be a binary, with further optical 'doubles'). In fact, Lyra is stuffed full of doubles, it's hard to miss them: http://bestdoubles.wordpress.com/2010/06/28/beta-lyrae-zeta-lyrae-and-even-eta-lyrae/

[Stu]

Nice one Andy, will have a good look at that later.

I do like the Other Double Double in Lyra, similar pairing to the original but much easier to split and different orientation. Just found it in your link :-)

http://bestdoubles.wordpress.com/2010/06/25/struve-2470-and-struve-2474-the-other-double-double-in-lyra/

Stu

[wxsatuser]

FWIW, I find this blog quite useful - well researched, with excellent descriptions - http://bestdoubles.wordpress.com/

As well as doubles, there are also multi-star systems too. While you're having a go at the Double-Double (Epsilon Lyrae), check out Beta Lyrae, which might be a multiple system (reports seem to vary - it may be a binary, with further optical 'doubles'). In fact, Lyra is stuffed full of doubles, it's hard to miss them: http://bestdoubles.wordpress.com/2010/06/28/beta-lyrae-zeta-lyrae-and-even-eta-lyrae/

Yep I follow that as well.

If anyone wants to print an atlas there is one here.

It's A4 pdf.....36 pages.......2000+ doubles.....15000+ stars to mag 7.....etc

[Roger Fairhurst]

Amazing the wealth of information available on SGL and the kind souls prepared to take the time and share it.

Thanks to all who contributed. I will be planning future sessions to include multiple star objects now - all I need now is clear skies. Not TOO much to ask ........... is it?!!

Kind regards

Roger

[Astro Imp]

 all I need now is clear skies. Not TOO much to ask ........... is it?!!

Probably 

[sheenoco]

Oh I did this by accident the other day! I just focused on a really bright star and then realised it was too. I shall look out for more now.

[Stu]

Nice out there at the moment, though packing in now. Managed to split Rigel nicely in the TV76 with 4.5mm Delos even though it was low over the neighbours house still. Might get up early for another look in the morning.

Stu

[CJ77]

Albeiro in Cygnus (Apologies if anyone above has mentioned it and I missed it), with its blue and gold double is always worth a look, and with it being more or less overhead for part of the night, and visible all year, I include it on my sky safari most nights that I'm out....  Lovely!!