Angular measurement

[chiaroscuro (Luke)]

Hi all,

I was wondering how to accurately measure the angular size of an object in the FOV, and also, how to accurately measure the angular distance between two points in space, either with the naked eye or through the scope. For instance, If a star chart says an object can be found 3 deg 30' 26'' from a known point towards another known point, how can I accurately measure that?

I've seen the estimates using palm width and finger width at arms length, and that the moon can be used as a reference at 0.5 degrees, but how can I be more accurate than that?

Thanks again for your help folks.

Luke

[el_draco (Rom)]

Check this out

http://www.meade.com/manuals/%20MA_1...ce_V011311.pdf

[raymo]

There are several ways of measuring your way around space. A good place to begin if you want accuracy, is to get an eyepiece with a graduated
reticle [ a bit like a scope on a rifle]. If you choose a couple of sky
objects of known diameter, you can work out pretty easily the angular
distance represented per graduation. This will vary of course with the
instrument with which you are using the eyepiece. If you use the eyepiece with a 2x barlow lens, then of course the angular distance will
double. You can use the eyepiece with your finderscope[if it will accept it]
to get a much larger field of view[typically 4 to 5 degrees], but again you would have to ascertain what each graduation represents.
Assuming that you are using an equatorial mount; if you want to find your way from one object to a second one that is a known distance
from the first one, you can use your setting circles. If for instance, you need to move 7 hours in right ascension and 2degs. in declination, note
the reading on the R.A. setting circle when looking at the first object ,
and move the scope 7 hrs. in the appropriate direction. Lock the scope
in R.A. by flipping the lever. Look at the reading on the DEC. setting circle, and move the scope 2 degs. in the appropriate direction.
That should be accurate enough to get the object you're looking for
somewhere in the field of your lowest power eyepiece, or failing that, if the object is bright enough, visible in your finderscope. Your accuracy
will improve with practise.
Hope this helped
raymo

[chiaroscuro (Luke)]

Originally Posted by raymo

There are several ways of measuring your way around space. A good place to begin if you want accuracy, is to get an eyepiece with a graduated
reticle [ a bit like a scope on a rifle]. If you choose a couple of sky
objects of known diameter, you can work out pretty easily the angular
distance represented per graduation. This will vary of course with the
instrument with which you are using the eyepiece. If you use the eyepiece with a 2x barlow lens, then of course the angular distance will
double. You can use the eyepiece with your finderscope[if it will accept it]
to get a much larger field of view[typically 4 to 5 degrees], but again you would have to ascertain what each graduation represents.

Hope this helped
raymo

Thanks raymo. So do most people use a reticle then? - I suppose that is most useful for smaller increments of measurement.

[chiaroscuro (Luke)]

Originally Posted by el_draco

Check this out

http://www.meade.com/manuals/%20MA_1...ce_V011311.pdf

Thanks el_draco. I'll settle down to a nice read tonight with that article. (Hope I can understand it.)