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Re: (meteorobs) Some Meteor questions




Hello, Asaf, and thanks for asking great questions! Trust me that there are
probably a lot of newcomers on our list who want answers to these same
questions... I'll do my best to answer you briefly here, but if anything is
still unclear, I have two suggestions:  1) Go out and try the following method
for yourself. It's FUN!  2) Read every modern meteor guidebook you can get your
hands on, e.g., IMO, NAMN, and AMS guides on the Web, the IMO Visual Observing
Handbook, George Zay's Handbook, etc.  3) Email our list with more questions!

-----------------

OK, here goes. First, you must record certain data about your SESSION before you
start recording the meteors you see...

When we talk about "recording our meteor sessions", we're really talking about
lying under the sky with a tape recorder handy, and recording most or all of the
meteor data for that night's observing session right onto the tape... Then later
on (in a nice, warm, well-lit room), we have to "transcribe" that tape - listen
to it, and enter all the data into a proper IMO report for mail/emailing... Of
course, the tape recorder is optional: clipboard and pencil work great too!

Now in order for your data to be SCIENTIFICALLY USEFUL to the IMO and others,
here's the data you MUST record on your tape (or onto paper if you prefer the
more reliable, "low-tech" recording method!) Print the following out, and next
time you try observing, use this as a checklist:

    1) Where you were observing from? Later after the session, you'll want to go
back out and find the latitude, longitude, and elevation of this observing spot,
so note down your location as specifically as possible.

    2) Which direction and altitude you were facing throughout the night? (If
this changes, say because you're avoiding the moon or clouds, note when!)

    3) The date and time you started AND stopped observing, to the *minute*?
(Use Universal Time if possible, rather than your local timezone time. But
either way, be sure to note WHICH timezone you use throughout.)

    4) The names of all meteor showers you know the radiant position and speed
for, and are actively WATCHING FOR, on that *particular* night? (To start off,
you may just want to keep track of the ONE MOST ACTIVE shower each night...)

    5) Begin and end time of each break you take? (A "break" is any period when
you're eyes are not CONSTANTLY on the sky.)

    6) Any cloud-cover or other obstructions that enter your FIELD OF VIEW? Try
to estimate these to the nearest 5%, with exact start and stop TIMES for each
period of cloudcover! Don't be TOO vigilant though: if cloudcover is changing
constantly, just try your best to make a few reasonable estimates.

    7) Your *naked-eye limiting magnitude*? Of all the information you can note
about your observing session, this is the MOST IMPORANT... There are a number of
convenient ways to estimate your "LM", but the only one recommended by IMO is
the "star count" method. Pick two "IMO Star Count" Areas high in the sky, and
count all the stars you can see with direct OR averted vision in each of those
two areas. REPEAT THIS EACH HALF HOUR throughout the night, in case your LM may
be changing due to weather or moonlight. There are 30 such Star Count Areas to
choose from. See the following Web site to see where they are:

        http://medicine.wustldot edu/~kronkg/namn/imocharts.html

-----------------

OK, you've logged all the session data you need: Now for the METEORS!

During your session, you should keep your eyes constantly glued to the sky. To
keep yourself alert (very important!), you should move your eyes and head
around; explore patterns in the constellations; look for naked-eye Messier
objects (star clusters for example); look out for the Milky Way, aurorae,
Zodiacal Light, Gegenschein, Zodiacal Band; watch for artificial satellites;
listen to music; listen for nocturnal animal sounds; chat with friends. But no
matter what you're doing to stay alert, ALWAYS KEEP LOOKING UP!

Then as SOON as you see a meteor, pick up your tape recorder (or clipboard), and
record the following data for that meteor (in roughly this order):

    1) Time you saw the meteor: exact time to the minute is useful, but if this
is too much trouble, just record a "marker" on tape or paper each 1/4 hour.

    2) Meteor magnitude: this is a measure of how bright the meteor was. You
measure a meteor's magnitude by comparing it to similar NEARBY STARS. The
magnitude of the star whose brightness is closest to your meteor's brightness,
is the magnitude you assign to that meteor! This is VERY IMPORTANT data. Without
it, your session probably WON'T be scientifically useful. Note that the
magnitude of a meteor is an indirect measurement of the MASS of the particle
which caused the meteor: thus by measuring magnitudes, you're really sampling
the flux, density and (indirectly) composition of a meteoroid stream.

    3) The meteor's relative speed: the simplest way to measure this is to
assign the meteor a number between 1 and 5 - 5 being as fast as the fastest
meteors you've ever seen, and 1 being as slow as the slowest. This 1-5 number is
really "subjective", but with practice, it becomes easy to assign. (Another
method advocated by SOME advanced observers is to directly estimate angular
speed for the meteor - in other words, its speed in "degrees per second".)

    4) What shower (if any) the meteor came from. You try to associate your
meteor with any showers you are currently watching, using THREE criteria
(outlined below). If you can't assign the meteor to any of the showers you're
watching that night, based on ALL THREE, you call it a "Sporadic" (or "random")
meteor. Criteria for shower association are: A) The meteor's path must trace
back across the sky to the "radiant point" for that shower. B) The meteor's path
must not be longer than half it's distance to that radiant point! C) The meteor
must be roughly the same speed as the shower - a 1, 2 or 3 if the shower is a
relatively slow one; a 3, 4 or 5 if the shower is a fast one; or a 2, 3 or 4 if
the shower is considered to be of "medium" speed.

    5) Any additional data you feel is worth noting (and you have the time to
record) about that meteor: whether the meteor had a "persistent train" - a
glowing trail left behind for a half second or more after the meteor passes -
and how long the train lasted; any color you noticed in the meteor or its train;
any fragmenting, "sparkles", or separate pieces that broke off the meteor; how
far the meteor was from where you were looking when you first noticed it
(so-called "DCV"); what constellation it appeared and ended in; any sound you
think was associated with the meteor, etc.

-----------------

Well, those are the basics... Obviously this is a LOT to memorize for your first
few sessions under the sky! So again, I strongly recommend those three things:
practice observing as often as you can; read the NAMN, IMO, Zay, and/or AMS
Guides; and last but not least, keep asking questions on 'meteorobs'.


And if ANYONE has more such questions, PLEASE feel free to ask! :)

Clear skies,
Lew Gramer


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