[vsnet-chat 5371] (fwd) Determining Limiting Magnitude

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

(fwd) Determining Limiting Magnitude

From: "Clay Sherrod" <sherrodc@ipa.net>
Date: Fri, 12 Jul 2002 13:01:09 -0500

Hello to all -
A nifty note....
Thanks to amateur astronomer David Snay we were "urged" into completing a
project that actually began back in 1974....determining the limiting
magnitudes of various aperture telescopes by simply using the stars
themselves....to include a SUMMER guide/test.

Since 1974 we have used and promoted a guide for autumn and winter skies
which is excellent for determining stellar magnitude thresholds down to the
mid-15's, via the Pleiades star field.  This has always been easy for
veteran as well as "newcomers" since the star field of the bright star
"Electra" has been used....easy to identify in the asterism of the "Seven
Sisters."

For the summertime skies, Brian Sherrod has finally compiled the mate to
this long-time winter test....this one using the constellation of LYRA,
dominant in the late spring and summertime skies, and high overhead for
mid-northern latitudes.

You can find this new - and very useful - tool at the Arkansas Sky
Observatory website by going to the homepage:  www.arksky.org and looking
for the "New Website Additions...." at the top of the page and click on the
topic.

Marked by its bright star, Vega, the observer need only to find the bright
stars SULAFAT and Sheliak to its southeast....it is between these two
conspicuous stars that the famous "Ring Nebula", Messier 57 is located!

Brian has used Sulafat's field of stars to provide a limiting VISUAL
magnitude test to magnitude 15.3 for telescopes
in the 10 to 16-inch range.

As with the WINTER Limiting Magnitude Guide -
on the Arkansas Sky site at:
http://vsnet.arksky.org/limmag.htm
this test is very objective as the observer fills out an essentially blank
chart using only the brightest stars as guideposts.  For complete
information on this test, please see the new posting.

By the way, this "test" makes and excellent club or school project for users
of many different sizes and types of telescopes....you will be amazed at the
differences in limiting magnitudes - not only with aperture, but also with
the type and style of telescope used as well!

Good luck, enjoy, and THANK YOU, Dave Snay!

Clay
----------------------------------------
Dr. P. Clay Sherrod
sherrodc@ipa.net
Arkansas Sky Observatory
www.arksky.org

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