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(meteorobs) Meteor appearance times
In a message dated 96-10-20 17:12:49 EDT, you write:
<<
Unguided exposures:
- accurate measurements because of absence of guiding errors. It
does not matter how long the exposure is, because you can simply correct for
the time difference between the start of the exposure and the time of
appearance of the meteor.
>>
--------
Marc,
One of the important difficulties for Unguided exposures is how accurate
start/stop times and meteor appearance times are recorded. For single station
work like what I do and probably for what most people do (because of the lack
of others to set up another nearby station )is mainly used for radiant
determinations. For guided cameras, I shoot this way for the ease of seeing
where the radiants might be as well as my hopes of getting a "good meteor
image with a normal looking sky...aesthetics". Start/stop times are usually
no serious problem in recording, but the meteor appearance times may be
difficult to obtain...especially if someone doesn't have a very quick and
reliable means to record the time. I'm not sure where I've read it, but I
believe Its desired to have a meteor appearance time to within 3 seconds for
unguided exposures and to within 30 seconds for guided. Again, if you are
just some smuck with primitive means to record times, it can become quiet
difficult to get meteor appearance times to within 3 seconds...especially if
you are trying to record other data as well. I do have a stop watch for this
purpose, but I can tell you from experience, that to remember to squeeze the
stop watch starting button as soon as you see a fireball along with doing
several other things, it becomes a real mental challenge. I've gotten the
knack down to a reasonable ability...but it's harder than it looks. It's
kinda like patting the top of your head with one hand and rubbing your belly
with the other at the same time....while walking, chewing gum and reading a
book as well...not very easy to do. With a guided camera, I have some leeway
for semi-inaccurate meteor appearance times. Now if I was part of a two
station set up, I can see where more accurate timing is important. Most
likely if anyone has advanced to a two station set up, they have more
reliable means to record their times. I normally use a 28mm lens...this also
helps to smooth over any small guiding errors that may show up. The larger
the lens, the bigger the errors will appear if exposed for the same length of
time. My exposure times are also adjusted to minimize any guiding problems or
star trailing. A preference of guided or unguided over the other is just
that really..dot it's mainly what you want out of the picture and what can be
gained from the exposure. With a guided, my reasons are to get a good
radiant alignment of a meteor and with a pleasing easy to use meteor image
that I would rather have on a good star -like background. With unguided, one
can acquire just as useful meteor data, but anywhere in the sky the stars are
just trails or streaks going in circles...boring after awhile...plus
appearance times need to be nearly balls on accurate.
George Z.