Re: [ccd-newastro] Splitting Stars/Viewing

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• Hi Rick, for seeing, take a look to Marc Sylvestre site page concerning determination of seeing by counting stars. It looks very accurate at:
Message 1 of 3 , Jan 4, 2001
Hi Rick,

for seeing, take a look to Marc Sylvestre'site  page concerning determination of seeing by counting stars.
It looks  very accurate at:

http://www.astrosurf.com/universia/Anglais/index1anglais.htm

Alain

"Foster, Rick" a *crit :

Hi Ron and CCD'ers

I hope this is not too far off topic or not appropriate for this list.
Please let me know if it is.

One other question, How do you determine seeing level?  Is it done by
whether or not you can see a star of certain magnitude? Is the star
twinkling or not?  If so, what is good seeing (assuming one has 20/20
vision)?

Thanks and clear/dark skies,
Rick Foster

• From the Celestron web site: For telescopes this is referred to as Dawes limit. It is the ability to separate two closely-spaced binary (double) stars into
Message 2 of 3 , Jan 4, 2001
From the Celestron web site:

"For telescopes this is referred to as "Dawes limit." It is the ability to
separate two closely-spaced binary (double) stars into two distinct images
measured in seconds of arc. Theoretically, to determine the resolving power
of a telescope divide the aperture of the telescope (in inches) into 4.56.
For example, the resolving power of an 8" aperture telescope is 0.6 seconds
of arc (4.56 divided by 8 = 0.6). Resolving power is a direct function of
aperture such that the larger the aperture, the better the resolving power.
However, resolving power is often compromised by atmospheric conditions and
the visual acuity of the observer."

Note that Dawes' limit is based on two stars of equal magnitude; if the
stars have different brightness, you may not get an accurate assessment. It
has been shown that in practice, modern telescopes often exceed Dawes limit,
especially at the high end.

Here are some links that you might find interesting:

http://www.umanitoba.ca/faculties/science/astronomy/courses/astro280/98R/Mik
e/calculations.html

http://www.atmpage.com/calc.html
http://www.ast.cam.ac.uk/gallery/observing/m13.html
http://www.seds.org/billa/lm/rjm.html
http://www.njaa.org/meteors/maglimit.html

The New CCD Astronomy Book
web site: http://www.newastro.com

-----Original Message-----
From: Foster, Rick [mailto:rick.foster@...]
Sent: Thursday, January 04, 2001 7:36 AM
To: 'ccd-newastro@egroups.com'
Subject: [ccd-newastro] Splitting Stars/Viewing

Hi Ron and CCD'ers

I hope this is not too far off topic or not appropriate for this list.
Please let me know if it is.

I would like to determine the relative resolution capabilities of my scope.
I understand that to a degree the smaller the distance between two stars you
can discern (minus the seeing level) the better the optics of the scope are.
Does anyone have the relative split in distance a scope should be able to
split by aperture size? I have a list of stars that are close together with
their separated values but I do not know to what level I should be able to
split. I have seen reference in books that you should be able to split
these two stars in say a 6". I have a LX200 10", F10. It does not appear to
grossly out of collimation yet (the secondary in an out of focus state is
centered).

One other question, How do you determine seeing level? Is it done by
whether or not you can see a star of certain magnitude? Is the star
twinkling or not? If so, what is good seeing (assuming one has 20/20
vision)?

Thanks and clear/dark skies,
Rick Foster

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