How to determine the mag of your skiy

I have seen several posts that indicate the mag of the sky in the viewing
area. How is this determined? Is it subjective?

MrB wrote:
I have seen several posts that indicate the mag of the sky in the viewing
area. How is this determined? Is it subjective?



Look on a chart and take note some stars of different magnitude. If you
see that star, you can say that your skie is of that magnitude

Clear sky...

MrB wrote:

I have seen several posts that indicate the mag of the sky in the viewing
area. How is this determined? Is it subjective?

It takes a little care to do it, but it isn't exactly difficult. All you do
is look up into the sky to an area near the zenith (ie: straight-up). You
carefully scan an area and see which are the *very* faintest stars you can see
with the eye (get dark adapted and use averted vision). You then locate these
stars on an atlas and get the data on exactly how bright they are from a
catalog (star-charting software is often good for this). The faintest star
you see is then your personal "Zenith Limiting Magnitude" (ZLM). The figure
you get will vary, depending on sky conditions and the observer. Moonlit
nights will often have a ZLM of 4.2 to 5.5, as will non-moonlit nights in
suburban environments, while a dark night well away from city lights might
have a ZLM as faint as 6.5 or even 7.0. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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"David Knisely" wrote in message
...
MrB wrote:

I have seen several posts that indicate the mag of the sky in the
viewing
area. How is this determined? Is it subjective?

It takes a little care to do it, but it isn't exactly difficult. All you
do
is look up into the sky to an area near the zenith (ie: straight-up). You
carefully scan an area and see which are the *very* faintest stars you can
see
with the eye (get dark adapted and use averted vision). You then locate
these
stars on an atlas and get the data on exactly how bright they are from a
catalog (star-charting software is often good for this). The faintest
star
you see is then your personal "Zenith Limiting Magnitude" (ZLM).

Some charts for this purpose are in my book, Celestial Objects for Modern
Telescopes, though you can use any charts that give you the information.
Mine are spaced so that one of them will always be within 40 degrees of the
zenith -- which is not always close enough for a good determination,
depending on your site. Next time they'll be closer...


--
Clear skies,

Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope

Many folks use the stars of the Little Dipper (Ursa Minor) as a guide, as
the main stars range from mag1-mag5, with an additional mag 6 star between
the mag 4&5.
Mark
"MrB" wrote in message
.. .
I have seen several posts that indicate the mag of the sky in the viewing
area. How is this determined? Is it subjective?

"Mark Forsthoefel" wrote in message
...
Many folks use the stars of the Little Dipper (Ursa Minor) as a guide, as
the main stars range from mag1-mag5, with an additional mag 6 star between
the mag 4&5.
Mark

That's an old British tradition. It doesn't work so well in the United
States, where the Little Dipper isn't very high in the sky. At my site it's
useless because a town is directly to the north, and I'm only at latitude 34
north.

I have seen several posts that indicate the mag of the sky in the viewing
area. How is this determined? Is it subjective?

Yes, it's subjective. Several folks have helped by explaining how to find a
single faint star to determine your naked eye limiting magnitude (NELM).
Another method is to count the number of stars you can see within a specific
area of sky. Here's a link to a site with charts and tables to help you convert
your star counts to a NELM: http://www.seds.org/nineplanets/lm/rjm.html

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
=============
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Thank you all.

"Bill Ferris" wrote in message
...
I have seen several posts that indicate the mag of the sky in the viewing
area. How is this determined? Is it subjective?

Yes, it's subjective. Several folks have helped by explaining how to find
a
single faint star to determine your naked eye limiting magnitude (NELM).
Another method is to count the number of stars you can see within a
specific
area of sky. Here's a link to a site with charts and tables to help you
convert
your star counts to a NELM: http://www.seds.org/nineplanets/lm/rjm.html

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
=============
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