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(meteorobs) Re: REPOST sky measuring sticks



Kim Y requested that I send out my post on sky measuring sticks again, so
here it is.  Meanwhile from this neck of the woods, I have been too busy
with tax season as usual to do any observing.  The weather hasn't been all
that great anyway : lots of haze and clouds.  Some evenings have been clear
enough to watch the great developing show of planets in the west.

With one minor clarifying alteration the repost begins here and runs to the
end :


The recent thread on measuring angles in the sky brought up some rather
involved mechanical methods of doing the measuring.  I have used the
following natural measuring sticks throughout my life, in degrees :

Pollux - Castor  5
head of Aquila  5
belt of Orion  3
Deneb - Albireo  23
open bowl of Big Dipper  10
pointers of Big Dipper  5
Mizar - Alcaid  7
W of Cassiopeia width  14
altitude of Polaris for my location - equals my north latitude to within one
degree

That's it.  Once these are known, you don't need to rely on body parts.
Southern hemisphere observers will need something additional that they can
see from there.   The short distances are far more important for meteors,
and I saw little discussion on these.  Once you reach 20-degree meteor path
lengths, a length to the nearest 5 degrees is sufficient.  I frankly can't
tell the difference between 39 and 40 degrees, for example, anyway.

The public is unable to judge any kind of angle.  They understand  "horizon"
all right.  The term  "overhead"  sounds like a precise term but it is
actually vague.  An uninformed person might say a bright meteor  "passed
overhead"  if it were as low as 65 degrees !  Just because your neck hurts
when you look up doesn't mean you are looking at the zenith.  Try deciding
where the zenith is just by looking up.  Then get a star chart with
declinations on it and find out where your zenith really is.  I could be off
by 10 degrees going by feel alone. 

 Any elevation between  "horizon"  and  "overhead"  the public tends to call
"45 degrees."  That is the best-known non-right angle angle.  Be suspicious
any time someone reports seeing something at elevation 45.  That happened to
me in one astronomy class ; a student saw a fireball in the north 45 degrees
up.  I went over to his place and had him point out where he saw it --
turned out it was only 15 degrees up !  It was below Polaris, which was 27
degrees.  That's quite an oversight when I had discussed this in class.

To plot meteors it is essential to know stars down to at least 4th
magnitude.  There aren't enough brighter stars to work with and get any
semblance of accurate plots.  Learning the constellations should be done
first.  I used the Rey book, The Stars : A New Way to See Them, the best
available, and had a good working knowledge of the sky in just four months.
A year of just recording some meteor data along with learning constellations
ought to be done before trying plots.   Few plots occur right between two
stars.  Most often I have to use a couple of stars that the meteor missed by
a degree or two to anchor the path.  I use a ruler against the sky.

Norman


Norman W. McLeod III
Staff Advisor
American Meteor Society

Fort Myers, Florida
nmcleod@peganet.com

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