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(meteorobs) Re: Angular Velocities
Daniel and All,
Rainer neglected to answer your questions concerning angular velocities.
I'll take a chance to answer your question as they are important when
providing plots.
The IMO suggests that you extend "in your mind" so that all meteors last
exactly one second. Therefore, if you see a meteor five degrees long,
lasting one half second then extending it to one full second would give
you an angular velocity of ten degrees per second.
This may be a bit difficult for novice observers. For those new to
observing, yet still wish to contribute full reports, I would suggest
starting out with the following method: First of all you still need to
estimate the path length as precisely as possible. Knowing the distances
between some of the brighter stars in your field of view helps
tremendously. For instance; if the bowl of the Big Dipper is within your
field of view then knowing that the "Pointers" (Alpha and Beta Ursa
Majoris) are five degrees apart will help with your estimates.
Now for the difficult part; you need to estimate the duration of each
meteor. I believe we are able to estimate with an accuracy down to .2 of
a second. Therefore I have created the following scale to help determine
the duration:
.2 second - the meteor is just a streak with no visible meteoroid (body)
.4 second - the meteoroid may just be visible but the meteor still
appears quite fast. For me, this is the most common duration seen during
my morning watches.
.6 second - the meteoroid is easily visible yet the path is usually short.
.8 second - the meteor now appears to move quite slowly.
1.0 second - the meteor lasts long enough that you may be able to turn
your head in time to follow it.
Once you have these two parameters you extend each meteor mathematically
to one second. You will need the correction factor (1.0/n) for each
duration (.2 = 5.0, .4 = 2.5, .6 = 1.67 and .8 = 1.25) For instance: a
meteor lasting .4 of a second traveling 5 degrees would result in a
angular velocity of 12.5 degrees per second (5 * 2.5 = 12.5)
A great majority of the meteors seen lie in the 5-15 degrees per second
range. If they are consistently above or below this range then you may
be overestimating or underestimating your angular velocities. One must
also realize that the upper limit for angular velocities is 38
degrees/sec. If your result is higher than this figure then either your
length is too long or your duration is too small.
Once again the IMO does not recommend using the mathematical approach
yet I feel it is a stepping stone to using their mental method.
I hope this helps!
Robert Lunsford
Daniel Gruen Wrote:
>Can anyone give me some advice on mesauring the angular speed of a
>meteor? I feel quite unsure about what is meant and how it should be
>measured. Are my plottings valueable without these data at all?
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