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Re: (meteorobs) meteor duration estimates
In a message dated 96-10-30 04:20:26 EST, you write:
>I agree with Jim and Norman, that estimating the duration of a meteor is
>not that a challange. After all, you also have to estimate the
>brightness of a meteor at one instant, so why shouldn't you be able to
>give a good estimate of it's duration? Once you have observed a collection
>of shooting stars you should be able to give it's duration with an
>accuracy of 0.2s or so.<<<
I believe that duration estimates from those who estimate within tenths of a
second are actually coming up with these estimates from the apparent speed
the meteor displays rather than actual sense of timings. There is actually a
thin line between the two, probably not realized by the observer. A skilled
observer who is capable of judging in "tenths" of a second is also
experienced enough to instinctively know what tenths of a second is expected
from various degrees from a radiant....in other words biased due to knowing
what is expected. But the purpose of my concern is to simplyfy speed
judgements to a level that is not way above their ultimate use...ie an aid
for shower determinations along with the other rules for such determinations.
With my beliefs that tenths of a second are ultimately judgements based on
apparent motions, it appears to me that angular velocity measurements that
are resulted from these tenths of a second "measurements" are nothing more
than a complicated speed scale. The speed scale scheme that I use is simple,
easy to use and I doubt any less accurate.
>Good questions, what those estimates are good for. It might help
>you for the determination of the meteor's angular velocity. You imagine
>how long the meteor would have traveled among the stars if it had lasted 1
>second, and then you determine that distance. I have no idea what else the
>duration could be good for. By the way, I normally record only unusual
>long lasting meteor, say larger than 0.5s or so.<<<
A meteor's angular velocity determination derived from visual means is not
accurate enough for any other purpose to my knowledge other than aid in
shower determinations. This kind of data used for anything other than shower
determinations is not good enough...other accurate means is needed such as
with radar or video camera systems.
>
>Last but not least there is a fine method of tunig your time estimates: By
>watching a video tape from a wide angle video system! Such tapes look very
>similar to what you see with your naked eyes in the sky. After you have
>estimated a meteor's duration you can replay the tape in slow motion and
>count the number of frames the meteor was visible on. From the hundreds of
>video meteors of MOVIE I have measured so far I found, that most meteor
>last between 0.2 and 0.3 seconds.
>Cheers, Sirko<<<<
Yes Sirko, but are you learning the time by how fast the meteor appeared to
move? With a little practice, I can simply say that a meteor appearing at a
certain speed has done so in so many tenths of a second. I find the numeric
5 scale method used in the groups of 3 scheme to be quite usable and with
little mental gymnastics. In using it, you aren't attempting to come up with
a velocity. But rather assign shower relationships based on a meteor's
apparent speed being within reason after other shower determination rules are
considered and along with a meteor's relationship to the radiant. I've had
quite good success with this method that I'm thoroughly confident in it's
use. It's definitely a lot easier to learn and use...and it's purpose is
fullfilled just as good as determining in tenths of a second to come up with
a deg/sec value or any other similar means.
George Z.