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(meteorobs) Re: REPOST sky measuring sticks

Norman's message reminded me of a discussion at the recent AMS workshop.
We were debating the use of elevation above the horizon verses zenith
angle (which is measured from the zenith downward toward the horizon).

It seems that zenith angle was (is still?) the preferred method. As
Norman suggests it is much more difficult to judge the zenith as even
experienced observers miss it by many degrees. This would seem to
indicate that elevation above the horizon would be a more accurate
method. 

The main objection the elevation is the lack of a true flat horizon.
Despite hills and mountains one may encounter I still feel confident
that most everyone could guess the true horizon to a much more accurate
extent compared to guessing the true zenith.

The reason for measuring such an angle could be for shower associations
or absolute magnitude determinations. 

Clear Skies!

Bob Lunsford

  

nmcleod@peganet.com wrote:
> 
> 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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