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Re: (meteorobs) Limiting Magnitude



Asaf,
        The limiting magnitude is determined, in theory, by the faintest
star visible to an individual observer.  Thus if an observer has very
good eyes and a very dark site, he/she could reasonably record LM's of
+7.4 or even fainter.  But everything depends upon the darkness of the
site and the ability of the observer to see faint stars.  I do not know
personally, but I could imagine that in Israel there are some very dark
sites in the desert, but not near settlements and towns where artificial
lights interfere.
       As LM's get better, the number of meteors visible goes up
dramatically.  Since you are young, you probably have very good eyes.
If that is true, then if you went way, way out where there were no
lights, not even a glow of light on the horizon,
you would see many, many more meteors than near your home.  Remember,
that these additional meteors will be rather faint.
An old fogey like myself  *may* not be able to EVER see stars as faint
as +7.4 because my  eyes just may not be capable.  So even if I went out
into the desert with you, you might see far more meteors (and stars)
than me (maybe).
     The +6.5 LM you refer to is the standard limiting magnitude used by
meteor researchers to determine the ZHR for given meteor showers. In
addition to radiant altitude, the  LM reported by an observer is
adjusted to +6.5 to determine how many meteors of the shower are
"falling" during a given hour.
     The standard method of determining an observer's LM is to count the
stars in certain regions of the sky, then look up that number on a chart
to see what the LM is.  For instance, at 09:15 UT this morning I counted
25 stars in a certain area in Leo the lion.  Then I looked this number
up on the chart and I found that my LM was +6.78 for *that part of the
sky*.  A good observer will count at least three of these regions, one
near zenith, one at about 40-60 degrees up, and one near the horizon to
get a much better idea what his/her total LM really is.  After all ,
meteors appear in any part of the sky, right? As an amateur astronomer,
you should learn to do this when you observe meteors.  To find the
charts to use, go to the following site...

http://www.imodot net/visual/major01.html#table2

...scroll down to "5.2  Determination of the Limiting Magnitude" then
click on  "table 2" for the list of charts, then click on any of the
blue numbers to see a chart.  Find a chart thatshows an area of the
skythat is out when you observe.  The table for converting your count is
found by clicking on "table 3."

Hope this helps!
Kim Youmans


Asaf Shtull-Trauring wrote:

> I always thought that the highest limiting magnitude
> is 6.5, but after hearing observations of different
> members on the Meteor Observing Mailing List, I'm
> interested on knowing- what IS the limiting magnitude,
> and who decided it's 6.5 magnitudes if it's not?
>
> =====
> Asaf Shtull-Trauring, Israel.
> Amateur Astronomer, ATMer & Meteor Observer.
>
> http://www.perihelion.com/
> Future Amateur Astronomy online community.
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