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Old 28-09-2011, 08:14 AM
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Rob_K is offline
Join Date: Oct 2006
Location: Bright, Vic, Australia
Posts: 2,126
Originally Posted by orestis View Post
Hi guys,

A very interesting thread and great tips.

I have a question though not deep sky related I hope this is okay.

In a lot of observing reports I see mentions of Apparant size of an object and was just wondering how to do this myself is it plainly estimations on your knowledge of your Eps TFOV or is it more complicated than that.

Thanks in advance
reagrds Orestis
Don't know about everyone else, but I use a few methods:

- First, knowing the FOV. If you've got a 1-deg FOV and a big object spans a third of it, then it's about 20' across.
- Sometimes in generating charts for small, faint objects, I obtain the distance between an obvious, reasonably tight pair of stars that will be close to the object in the field (many planetarium programs like Starry Night have this 'ruler' function).
- Also, having done that many times, you can get a fair gauge on distances between close star pairs in the field at a certain magnification and use that to estimate size.

Now finding north to add 'directions' to an observation is a different problem, using a reflector & an alt-az mount!

Cheers -
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