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(meteorobs) WHAT TO RECORD (Re: Leonid meteors on 18/19 Nov (Mon night/Tue morning)
Joseph Rothchild of the ATMs of Boston asks:
>I will again be trying to do some counts of the Leonids
>this year. Last time I did 10 minute intervals. Could
>you let me know again what other information I need to
>gather for it to be useful data?
My pleasure, Joseph! Here is a "short list", followed by
a description of each item. If you have ANY questions or
suggestions, don't hesitate to email me. Here's the list:
1) DO NOT COMBINE DATA WITH OTHERS (no "group counts")
2) Location where you observed
3) Limiting Magnitude to roughly 1/10 of a magnitude
4) Start and end times to the minute
5) Field obstruction within 10%
6) Direction and altitude you were facing
7) Try estimating METEOR magnitudes!
Note also: If you have a Windows PC and you would like to
PRACTICE doing meteor counts, try out this neat software:
ftp://www.imodot net/pub/software/metsim/
Here are the longer descriptions, if you want more detail:
1) Don't combine data with other observers
In order to compare your observations with those of other
observers around the world, and to use them in any kind of
analysis, you must ONLY count the meteors that YOU see...
If you make "group counts", it can be fun, but your counts
just won't be useable for posterity.
2) Location where you observed
Record where you are when you're observing... Later on,
after you're done observing, you can go online and find
out the exact latitude, longitude and elevation of your
site. (For the observing sites of our local clubs, this
information may already be on the Web, or known to you.)
3) Limiting Magnitude to roughly 1/10 of a magnitude
One of the most important pieces of data, to record more
than once throughout your session, is your own personal
visual "Limiting Magnitude": estimating this within a few
tenths of a magnitude is extremely helpful, in comparing
your result to those of other observers around the world.
To do this, the only reliable method is by counting stars:
pick one of the standard "IMO Star Count areas" near your
field of view, and count all the stars in that polygonal
area (including the vertex stars), at least once an hour.
Ideally, if you're skilled in the Counting technique, IMO
suggests you count TWO different areas each HALF hour...
All this is easier said than done if a STORM'S going on! :>
Here are the counting areas all around the sky:
http://www.seds.org/billa/lm/rjm.html
In the pre-dawn hours of 19 Nov, you'll probably face your
lawn chair East to keep the moon out of your eyes. In that
area of the sky, I'd think the easiest Count Areas to find
and memorize are #9 in Leo, #3 in Ursa Major, #4 in Gemini:
http://www.seds.org/billa/lm/rjm9.html
http://www.seds.org/billa/lm/rjm3.html
http://www.seds.org/billa/lm/rjm4.html
(Here is a nice chart showing all these areas together:
http://www.imodot net/visual/2a.gif )
NOTE: The *Tables* at the SEDS site above are NOT accurate
any more. If after your observing session you want to look
up your "LM" based on your Counts, use this table instead:
http://www.imodot net/visual/lm.html
4) Start and end times to the minute
And of course, getting exact start and end times for each
interval over which you count, is very important. That is
after all, what allows scientists to figure out just how
close to correct their "to the minute" forecasts were! :)
Ten minute counts are very helpful during periods of high,
but sub-storm level, activity: when the 10 minute counts
start to go above 50, consider switching to 5 minute count
periods. And when the 5-minute counts go over 50, if you
can deal with it, 1-minute counting intervals are best...
Naturally, to make this feasible, you really need a clock
which is accurate, and can be set to sound a "ding" every
one minute, every 5 minutes, and/or every 10 minutes...
5) Field obstruction within 10%
Beyond that, if you have any obstructions (clouds, trees,
the Clubhouse roof, whatever), estimate total percentage
of YOUR field of view (NOT the sky) that is covered.
6) Direction and altitude you were facing
Note that if you wish to count during the whole time Leonid
activity is going on (~ 10pm to dawn), you may want to move
your lawn chair (and/or angle it higher or lower) throughout
the night. Just keep a simple note of where you face, e.g.,
"At 10pm, I faced South with my eyes facing 60o altitude. At
3am, I switched around to face due East at about 60o."
7) Try estimating METEOR magnitudes
Last but not least if you want your data to be a REAL boon
for researchers, try estimating and recording a brightness
for each meteor! This is actually easier to do than people
generally assume: with a lot of practice beforehand, I was
able to record a magnitude for EACH of the 4,000 meteors I
saw in China during the Asian Leonid Storm of 2001!
This is especially useful (and also much, much easier) just
before and AFTER a storm has occurred.
To practice doing this, all you have to do is memorize the
magnitudes of a few handy comparison stars, and then get a
"feeling" for each meteor's brightness by comparing it with
those stars the instant you see it! Here is a handy set of
charts with good comparison stars for meteor observing:
http://www.namnmeteors.org/charts.html
Clear skies!
Lew Gramer (GRALE), IMO, NAMN
owner-meteorobs@atmob.org
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