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Anonymous
Unregistered
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Hello all
I need help with the definition of an arcsecond. I am looking through my books to find stuff and i see that something is for example 13 arcseconds north od such and such. How to measure and arc second?? Any inforemation would be greatly appreciated.
Thanks, AJ
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jrcrilly
Refractor wienie no more
Reged: 04/30/03
Posts: 30716
Loc: NE Ohio
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There are 60 arcseconds in an arcminute. There are 60 arcminutes in a degree. 360 degrees is once around the celestial sphere. Or did I misunderstand the question?
--------------------
John C
Battle Cry of Reno
http://www.wadsworthobservatory.com
My Cloudy Nights gallery
AT12RC
AT65EDQ
QSI683WSG-8
Roper Scientific Quantix 6303E "project" camera
mystery EQ mount on the way
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Michael_Swanson
super member
Reged: 04/23/03
Posts: 192
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Hi folks,
John hit the meat of the technical definition, now to answer how this is applied to the question of what to do to measure arcseconds or arcminutes at the telescope. In other words, how do you find something when you read that "14 arcminutes to the north you will see a small splattering of stars that are the open cluster NGC 1234".
First off, when you see a position direction like 'north', this indicates move towards the north celestial pole (the 'north star'). As far as the angular distance (14 arcminutes), you will need to learn the true field of view (TFOV) of your various eyepieces when used in your scope.
For that, I'll point you to an article I wrote for our local astronomy club. Go to
http://www.NexStarSite.com/rac.htm
Click the link for articles, and read the article "Useful Formulas for Amateur Astronomers". Note the reference to the Scope Calculator spreadsheet (Excel format) available in the Downloads section of the web site.
Best regards,
Mike Swanson
Author of "The NexStar User's Guide"
Author of "NexStar Observer List"
http://www.NexStarSite.com
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Chutzpah
sage
Reged: 08/26/04
Posts: 228
Loc: Cheshire, UK
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Here's an example. If you use the common or garden plossl, the field of view quoted by the manufacturer is often 52 degrees. You divide this by your magnification to get the true field of view, so in my 8" f6 newt a 10mm plossl with 52 degree fov would give 120x mag with 52/120 or 0.43 degrees fov. That's around about 26 arc minutes, so to use your example above (14 arcminutes) I would know that I'd need to move north by just over half the distance I can see in my eyepiece.
It's a bit of a nightmare at first trying to figure all this stuff out, and I'm still a beginner myself. It helps, though, to check things on a starmap and imagine your FOV with different eyepieces and what you'd see through them. Personally, I cheat and use the projected eyepiece views in Starry Night  It was doing this that helped me spot my first DSO (M51), as otherwise I'd never have believed the faint puffy cloud-like thing filling my whole eyepiece was actually a galaxy.
Good luck with all the other astro-gubbins!
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Stevie
8" f6 Newt
MN56 5" Mak-Newt
10x50 binos
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