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Re: (meteorobs) Plotting: Three Stooges Method
Kim & All,
No one said plotting was easy! This is why we suggest that newbies wait
until they have spent considerable time under the sky learning the
constellations before attempting to plot.
The most important thing to do is to get the plot drawn on to the chart
as soon as possible. Don't worry about time or any other parameter. Get
the meteor drawn ASAP! I have my clipboard lying on my lap so it can be
grabbed at a moments notice. A pencil and transparent plastic ruler are
also attached to the clipboard. I also have a two foot long (61 cm) dark
cord with loops knotted in both ends lying across my chest. I have a
small and very light Mag-Lite tied to a string around my neck so I won't
lose it in the dark.
The moment I see a meteor I grab the dark cord and line it up with the
meteors path. I look for two recognizable stars that line up with the
path so that I can use them as guides on the chart. This usually takes
10-20 seconds depending on the area of the sky. Note that I have not
taken
my eyes off the sky so no time has been lost so far.
Once I have this memorized I reach for the flashlight and place it in my
mouth. That third hand helps immensely! I then reach for the clipboard
with my right hand and hit the button on my talking clock with my left
hand. Now that I know the time I remove the pencil and ruler from the
clipboard line the ruler up with the same path on the chart. The tricky
part is getting the correct length but after practice one becomes
proficient.
This usually takes 15 seconds after which I enter the magnitude and
other
data on a separate data sheet. My eyes are off the sky for approximately
30
seconds. This is the most likely time that the -7 fireball will appear
:)
I know that this sounds like a pain but it becomes second nature after a
few sessions.
As for finding radiants on the Brno charts, any star atlas or
planetarium
program can show you the exact area of the sky. Simply find this area
using
and celestial coordinates and then make some kind of mark on your chart
to
indicate the radiants position. It is a good idea to do this before the
observing session so that you can classify any meteors that appear too
far
from the center of your field of view. If they are too far away for an
accurate plot you can still use the cord to get an estimate of the path
and
an idea whether the meteor belonged to any shower.
As for the original 11" X 17" Brno charts, a line 2.8 mm represents one
degree at the center of the each chart. Mine are reduced to 77% of the
original size for more convenience in the field. This reduction yields
2.2
mm per degree at the center of the chart. Naturally on gnomic charts
lengths
will increase as you move away from the center of the chart. Here are
some
more lengths for areas further from the center for the original 11 X 17
charts:
50mm = 3.1 degrees/mm
100mm = 3.9 degrees/mm
120mm = 4.4 degrees/mm
150mm = 5.2 degrees/mm
170mm = 5.9 degrees/mm
200mm = 7.1 degrees/mm
220mm = 8.1 degrees/mm
The charts in the handbook appear to have been reduced to 2/3's the size
of
the original so the figures above would need to be multiplied by 0.67 to
match the charts in the handbook. This gives the following results:
0mm = 1.9 degrees/mm
50mm = 2.1 degrees/mm
100mm = 2.6 degrees/mm
120mm = 2.9 degrees/mm
150mm = 3.5 degrees/mm
170mm = 4.0 degrees/mm
200mm = 4.8 degrees/mm
220mm = 5.4 degrees/mm
Finally, for me a 12" ruler held at arms length would represent 32
degrees.
How did I come up with this? I looked in an star atlas for two bright
stars
precisely 10 degrees apart. Once I found them I took a 6mm thick
aluminum
rod and cut it until both stars appeared on each end of the rod. The rod
ended up being 96mm long which is 3.78 inches. It's seems that my hand
and
arm length is a little smaller than Greg's.
Altair and Deneb are approximately 35 degrees apart so it seems that Kim
and I have similar hand size and arm length.
The current Piscid radiant lies at 354 (23:36) -7.
Clear Skies!
Bob Lunsford
"Kim S. Youmans" wrote:
>
> Hello All,
> As part of my continuing education in meteor observation, I
> have slowly been working my way into plotting. I must admit, never have
> I found anything that seemed so deceptively simple to be so
> confoundingly frustrating. A typical attempt at plotting a single
> meteor may go something like this:
> 5:40 UT, a meteor appears that *may* be coming from a known
> radiant. I decide to plot it. I throw my ruler up into the air to
> "place" the path.
> 5:40:30, I feel I have the path, now I need to see the time. I
> grope for my recorder, finally find the pause button, while still
> holding the ruler to the sky. I look down at the watch glued to the
> recorder. I look back up, and I no longer have the ruler placed exactly
> where it should be. I place it back where I think it should be.
> 5:41:30 I stare and stare and stare at that region of the sky and
> finally realize the meteor was over the peak of Ophiuchus.
> I cautiously put the ruler down and reach for my red light and charts.
> I turn on the red light, and in order to free up my hands for plotting,
> hold the light in my mouth. I get stung on the tongue by an ant. I
> spit the ant and several grains of sand out, then return to the chart.
> 5:42:30 An outburst of 15 simultaneous meteors occur while I am
> staring down at my charts. By now I can't remember
> which direction the meteor was traveling, or what the beginning and end
> point was, if I ever had them well to begin with. I "plot" the meteor
> just as the cat jumps on my lap and all my tools get scattered.
> 5:43:30 A magnitude -7 fireball appears while I am looking down to
> gather up my pencil, chart, ruler and recorder. My chewing gum, I
> notice, is quite gritty with sand now.
> And that was an EASY one! Actually, most of the meteors appear
> within my field of view, and go quickly on the chart I have out and I
> don't really lose that much time. But the most frustrating thing of
> all, I think is getting home and not being able to accurately predict
> the radiant drift for various minor shower radiants due to the
> inadequacies of my charts. I still don't know what one grid on the
> Atlas Bruno chart represents, in degrees, and my Petersons charts have
> the RA and dec, but I can't translate that well into actual degrees.
> So a few questions: If I hold my 12" ruler to the sky at arms
> length, how many degrees of sky am I covering? It is approximately the
> distance from Deneb to Altair. I know the rule of thumb about fist size
> being 10 degrees and open hand being about twenty, but there can be a
> wide variation there among individuals.
> Also, do I need to join a guild or a lodge to get the secret
> information contained within those plotting charts? If I could
> accurately measure distance on those charts, I wouldn't have to
> aggravate Mark, Wayne, and others for current radiant positions. Or is
> there some easier way that I'm missing altogether? (Wayne, I didn't get
> the current Piscid position:>)
> But until I started plotting, I never realized I had so many thumbs.
> Thanks in Advance, Kim S. Youmans
>
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