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Frustration of double star observing

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#1 npc

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Posted 21 March 2014 - 03:00 PM

The primary focus of my observing is DSOs, but during times of bright moon and when under bright skies (like when I'm at home), I turn to planets, carbon stars, and double stars. There's one thing I find very frustrating about observing double stars, and that's being certain I'm looking at the right thing when viewing less well known doubles.

Here's an example. Some observing guide or catalogue somewhere lists Taygeta (19 TAU) as a double star, so I put it on my "to view" list. It's star #6 of the Pleiades. I have it listed as mag 4.3/8.1 with a separation of 72". (Taygeta also has a close companion that is beyond my equipment's ability to separate.)

To me the B star is not at all obvious. I have a candidate, but I can't find any source that will tell me if I'm right. None of the books I have and no online resources I've looked at provide any help, and the WDS catalogue doesn't seem conclusive. I'm not even sure it actually has a companion.
Anyone have a clue or a resource that might provide some assistance? How do serious double star viewers handle this situation generally, besides stick with the "tourist trap" doubles for which there is a plethora of information?

#2 Ed Wiley

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Posted 21 March 2014 - 04:51 PM

Bring up a POSSII image in Aladin. Call up the WDS catalog. Use the measuring tool to see which star is "B" in the picture. At the scope make sure the orientation is the same as the view.
Ed

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#3 cbwerner

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Posted 21 March 2014 - 09:39 PM

Ed,

I just downloaded Aladin - I can't figure out where to get a POSSII image, and can't find any reference to that in the FAQ or instructions. Can you direct me? Thanks.

#4 azure1961p

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Posted 21 March 2014 - 11:21 PM

Learning to read position angle at the eyepiece (simple enough) and having the data on hand (Stelle Doppie/WDS) makes straightforward work of this kind of thing. There ARE discrepancies but overall its easy enough.

Pete

#5 npc

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Posted 22 March 2014 - 02:45 AM

Learning to read position angle at the eyepiece ...


Having an automated alt-az mount is probably the least convenient combination for this. If I had an equatorial mounted scope this would be a lot easier.

#6 WRAK

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Posted 22 March 2014 - 03:55 AM

Taygeta is with 72" rather wide and therefore not such an interesting target as the visual impression in the scope is maybe of two stars somewhat close but not of a "double" - and sometimes it is really difficult to identify such a wide companion especially in a field rich of stars as in an open cluster. Doubles with smaller separations needing some magnification for resolution are certainly more interesting and same time it is much easier to identify the correct companion.
If you are really interested in double star observing you might consider a session planning software giving you the correct image for doubles with all components including alt/az rotation for your given location and time.
Wilfried

#7 Ed Wiley

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Posted 22 March 2014 - 10:54 AM

Ed,

I just downloaded Aladin - I can't figure out where to get a POSSII image, and can't find any reference to that in the FAQ or instructions. Can you direct me? Thanks.


Hi Chris: File -->Open. See the screen shot below. You need coordinates, then select an image to look at in the main window. It will pop up in the screen. You load catalogs by going back to the Server Selector screen. Most direct way is to simply fill in "wds" (or catalog of you choice if yo know the name) in the catalog window. Otherwise you can select a menu (All VizieR, etc) that gives you choices.

There is an Aladin tutorial and it takes a bit of time to master the basic functions, but it is well worth the effort as there are bunches of data from catalogs that can be directly associated with the images.

Ed

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#8 cbwerner

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Posted 22 March 2014 - 07:52 PM

Thanks Ed!

#9 Ed Wiley

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Posted 23 March 2014 - 10:07 AM

You are welcome, Chris: glad to help with additional questions if needed.
Ed

#10 drollere

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Posted 24 March 2014 - 11:26 AM

this thread highlights a basic tension in visual astronomy -- whether you rely on software to do work for you, as ed advises, or use an acquired skill with equipment and observing to solve the problem, as pete suggests.

the ability to recognize field orientation is a basic skill in double star astronomy, as i describe >here<.

all that's needed in addition is a source of double star information that provides accurate position angle information. these sources include the WDS, for example in the spreadsheet version downloadable from my site, or sissy haas's excellent reference, or many planetarium software programs.

an altazimuthal mount creates specific difficulties, certainly. but they are hardly insurmountable. if you have an altazimuthal mount then you are likely using a mirror diagonal, which means the field is just reversed left to right and position angle runs in the clockwise rather than counterclockwise direction. you need to know where celestial north is, and finally where the position angle takes you in relation to celestial north.

to solve that problem, i simply look at the spot in the sky where my telescope is pointed, hold one hand so that my palm and fingers are vertical to the ground, and hold my other hand across it in the direction of the pole star. if you look down into the diagonal while standing directly behind the telescope, that angle, reversed, is north in the eyepiece field of view, and position angle, counted clockwise in relation to it, is the direction that you should be looking.

you are unlikely to be able to access VizieR in the field, or even in your driveway, which means ed's approach makes you a daytime desktop astronomer. this limits what you can "solve" at the eyepiece to what you planned to look at in advance with the software.

notetaking and drawing are also underrated skills. if you make a quick sketch of the field, with the ambiguous objects and north indicated, or describe the problem in a notebook or tape recorder, you can use the computer the following day, as ed excellently explains, to resolve any questions.

#11 Rich (RLTYS)

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Posted 25 March 2014 - 07:12 AM

notetaking and drawing are also underrated skills. if you make a quick sketch of the field, with the ambiguous objects and north indicated, or describe the problem in a notebook or tape recorder, you can use the computer the following day, as ed excellently explains, to resolve any questions.


This is exactly what I do. :bow:

Rich (RLTYS)

#12 Ed Wiley

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Posted 25 March 2014 - 09:55 AM

Good advice, Bruce. Naturally, resources such as Aladin are not a substitute for understanding directions and scale at the eyepiece.

Ed

#13 cbwerner

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Posted 26 March 2014 - 12:20 AM

Good advice, Bruce. Naturally, resources such as Aladin are not a substitute for understanding directions and scale at the eyepiece.

Ed


Well said, both of you. When you are beyond a noob like I am on double stars at this point, simply being able to see and assess the various resources that are out there is a huge plus to getting my head around the process and challenges, regardless of how or even if I ultimately incorporate them in my observing.

And speaking of great resources - Bruce, the astro part of your site is a real joy and a tremendous asset, one that obviously took a pile of time on your part. Thanks for making your hard work available for me and others.

#14 blb

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Posted 26 March 2014 - 03:16 PM

Learning to read position angle at the eyepiece ...


Having an automated alt-az mount is probably the least convenient combination for this. If I had an equatorial mounted scope this would be a lot easier.

The type of mount that you have makes no difference at all. Learning to tell dirrections in your field-of-view and knowing how wide your field-of-view is with each eyepiece is the starting point for any observation. Making a sketch of your field-of-view showing directions will enable you to accurately estimate seperations and position angles with the knowledge of direction and width of the field-of-view. You can estimate seperation and position angle at the eyepiece without sketching but you MUST know the directions in your field-of-view and the width of your field-of-view to do this.

Just for starters, with out a drive, the stars drift out of your field-of-view on the west side and north will be 90 degrees to this direction either clock-wise or counter clock-wise, depending on your type of telescope. Hey, this is basic information we all should learn and use. This type of knowledge enables us to accurately describe what we are looking at and share that knowledge with others as well as confirming what we are seeing.

#15 Ed Wiley

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Posted 26 March 2014 - 09:00 PM

I think I will try a lazy way next time the clouds clear. On my tablet I have Sky Safari. It has a finder feature with cardinal directions. If I set it to my finder eyepiece FOV and set the view to "horizon" it might just show me the directions. This would have to be checked with traditional methods. But if it works, then I might get lazy real quick. :grin:

Ed

#16 blb

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Posted 27 March 2014 - 09:23 AM

I think I will try a lazy way next time the clouds clear. On my tablet I have Sky Safari. It has a finder feature with cardinal directions. If I set it to my finder eyepiece FOV and set the view to "horizon" it might just show me the directions. This would have to be checked with traditional methods. But if it works, then I might get lazy real quick.

Ed

And what will we do when the gadgets fail to work or the batteries run down. It is so easy to learn but we are so lazy. So sad.

#17 Ed Wiley

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Posted 27 March 2014 - 10:16 PM

Lighten up Buddy. It ain't all that serious.

Ed

#18 drollere

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Posted 27 March 2014 - 10:28 PM

star drift, when the servo mount is turned off, is of course a good way to identify east-->west (following-->preceding, in the traditional terminology).

personally, i don't use it, because with my meade handset there is quite a lot of button pushing necessary to get from the celestial coordinate goto input to the "sleep" function that turns off the drive, and back again. it gets old really fast.

if you just lift your head up and look at where the scope is pointing, then figure out where the pole star is, it is pretty easy to visualize the angle between the a line from the pole star to the target and a line vertical through the target (perpendicular to the horizon). i just model it with my flattened hands until both hands ("lines") look right.

i can normally guesstimate to within about +/-20º of the catalog values of position angles, which is close enough to identify a faint companion like sirius B or note the position of an odd feature. but with an properly aligned equatorial mount i never have an error greater than +/-5º ... no hands required.






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