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solargenes
newbie
Reged: 11/05/07
Posts: 4
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Hi, hope someone can shed some light on position angles. Was looking at Otto Struve 525. If I have North and East marked correctly, than the secondary is North and just slightly east of the primary. The way I determined North is by noting the direction setting in the Bisque software. Any confirmation, correction, or clarificaiton is most appreciated. Many thanks. Julie
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acafar
member
Reged: 06/17/06
Posts: 57
Loc: Madrid, Spain
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Hi, at the coordinates of STT 525 there are two pairs (in fact three, but I think the third is too faint):
- STT 525 AB m1: 6.14 m2: 9.12 sep: 1.8 pa:128
- SHJ 282 AC m1: 6.14 m2: 7.60 sep: 45.0 pa:349
The first one (Otto Struve 525) is a very difficult pair, which requires a lot of magnification and a very steady night. The second one (SHJ 282)is an easy pair that can be split easily with any telescope at low magnification. If it was the second pair, the position angle is 349 which means that the secondary is at the north as you mention, but slightly at the west (0-->north, 90-->east, 180-->south, 270-->west).
Remember that in many telescopes if north is up then the east is at the left and not at the right, due to the optical configuration. This makes things more difficult determining position angles. If you have determined the north and want to be sure about the west direction simply turn off the telescope drives (if you are using any) and left the star drift across the eyepiece.
Hope this helps,
Rafa
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Rafa
Vixen 4" Sf f/9,Scopos 2.5" f/6
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solargenes
newbie
Reged: 11/05/07
Posts: 4
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Many thanks.. that does help a great deal. Was trying to get away from having to turn my scope off and back on because am thinking i will have to realign everything, but that maybe the best way to get the directions correct. Thanks again.
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Rafa:
If you have an equatorial mount, you could just slew it east slightly and then back to see where West is in your field. Slewing east makes the stars appear to drift west as they would if the mount were stopped. This won't work for an alt-azimuth mount, unless it is go-to, in which case you could select an RA slighlty to the east to get the same effect.
North will always be either counterclockwise or clockwise from west depending on whether your scope has an even or odd number of reflections. (Or maybe it's the other way!  ) Anyway, it is always consistent.
To visualize PA, draw an imaginary line starting at the primary, through the secondary, and then note where it falls in relation to the cardinal directions in the field.
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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manyworlds
journeyman
Reged: 08/05/08
Posts: 6
Loc: Central Oregon
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Many thanks.. I think I'm getting there..  I'm using an ETX125, which has an odd number of reflections. So I can find East using the drift method, and North will be 90 degree counter clockwise to East. If you would 'true that', or continue to enlighten me, I will be delighted. Many thanks!
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RLTYS
Carpal Tunnel
Reged: 12/18/04
Posts: 1728
Loc: New York (Long Island)
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manyworlds
Welcome to the Double Star Forum. From where you observe I would guess you know which direction is north. To confirm your directions just nudge you scope slightly toward the north. I do this with my 10" dob to confirm north and south.
Hope this helps.
Rich (RLTYS)
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10" F4.8 Refl.
4" F5 Refr.
50mm F12 Refr. (Tasco #6TE-5)
12x63 and 10x50 Binoculars.
"I want to do more then just look."
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manyworlds
journeyman
Reged: 08/05/08
Posts: 6
Loc: Central Oregon
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Thanks for the information. Was trying to find a different way to confirm directions without having to nudge my scope or turn it off and back on. Seems like that is the last thing I would want to do after finding and splitting a double. Anyway, I'm new at all of this, so will try it.. am sure my fears must not be real, or all of you wouldn't be suggesting basically the same thing! 
thanks again. julie
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Jeremy Perez
Carpal Tunnel
Reged: 08/12/04
Posts: 1660
Loc: Flagstaff, Arizona, USA
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Hi Julie,
For your ETX, you noted north would be counter-clockwise from east, and that sounds right. Nudging north is a nice verification that you've got your scope's cardinal directions ironed out. Once you're comfortable with your scope's optical personality, you'll just know automatically where to mark north once you've determined east-west, with no nudging required.
When marking a double star drawing, I prefer to base things off of 'west'. That way, if I place a star at the center, it will drift and exit the field at the exact point I want to mark west on my drawing. Basing the directions off an east mark might be a bit less precise. (Somebody correct me if I'm not thinking that through all the way.)
Otto Struve 525 is one of my earlier double star observations. At the time, I hadn't researched beyond the details in the Astronomical League list. So I hadn't tried to look for the tighter 2 arc-second pair that Rafa detailed. Instead, I drew the wide pair (which is apparently SHJ 282!). In that case, I saw the secondary as just a bit west of north. It looks like I need to draw a bead on this one again soon!
I hope you're enjoying your immersion in double star observations!
Edited by Jeremy Perez (08/20/08 04:10 PM)
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manyworlds
journeyman
Reged: 08/05/08
Posts: 6
Loc: Central Oregon
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thanks very much for the information. once the clouds (and the smoke in central oregon)clear up a bit., will experiment some.. am sure it will all fall into place!
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