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(meteorobs) Re: local time
>Living in Fairbanks Alaska 00:00 UT to 04:00 UT =3:00PM to 7:00PM is this
>the expected max time
Negative.
>or is midnight to 04:00am local time the expected max?
Correct. "Expected max" is being used here to mean "highest observed
rates at that location."
I used the term "local time" loosely and colloquially in my post to be
very general. For this purpose, use whatever time is showing on your own
clock, assuming it is correctly set for your time zone. It works well for
the Geminid meteors because of the maximum being a day wide. Thus the best
shower rates come when the radiant is highest in your sky. That period is
about 4 hours wide also -- a generous opportunity.
There is a more exact meaning for "local time." If your longitude is
exactly divisible by 15, then "local midnight" coincides with your clock
reading of midnight. Longitude 75W is the standard meridian for the Eastern
Time Zone, for example. If you don't live right on your standard meridian,
then the clock reading for local midnight will differ : coming earlier if
you are east of your standard meridian, later if west. The longitude of
Fort Myers, Florida is 82W, which is 7 degrees west of my standard meridian
(75W). The correction is 4 clock minutes per degree of longitude
difference. So local midnight in Fort Myers is delayed 4 X 7 = 28 minutes,
hence my clock will read "12:28 am" at local midnight here. We won't get
into how "midnight" itself is determined -- this is already complicated
enough.
I observe from a site half a degree of longitude further east (81.5W), so
the correction is 26 minutes (4 X 6.5) at that location. That is why my
hours of observing meteors always go from minute 26 to minute 26. Changing
locations means I also change the time of my observing hours. That way the
earth has the same orientation relative to the stars, and I can directly
compare my observing hours from different places in different years. I was
trained to do it this way from the start and have always used it. But it's
not something that beginners or casual observers have to be concerned with.
Even the experienced observers don't use this technique any more.
Norman
Norman W. McLeod III
Staff Advisor
American Meteor Society
Fort Myers, Florida
nmcleod@peganet.com
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