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Re: (meteorobs) Which 'datum' to use for meteor report long...
Lew Gramer wrote:
> >(Folks may argue that such accuracy is not necessary for visual observing,
> but
> >since I've never heard a definite statement to that effect from IMO, I always
> >try to report my position within a second of arc and ten meters elevation.)
Jim Bedient wrote:
> Needed accuracy is directly related to what use will be made of the
> information. In individual visual observations, I don't see any real need
> for accuracy greater than the nearest degree,
Right. An accuracy of 1 arc minute is definitely enough, even
10 arc minutes don't cause much of an additional error. When introducing
new sites to the VMDB I usually check for nearby places which may
be in a distance of up to 10 miles. If there is something closer,
I do not introduce a new site.
> When considering two-station work, it is obviously more critical
As the astrometric accuracy is well below 1 arc minute, the location
should be given with better accuracy than this, say 1". Note the same
holds for the times recorded, which in fact provide another spatial
coordinate of orbital computations. An accuracy of recording times
with 1-sec accuracy is recommended. For a comparison: The Earth
moves 0.0001 degrees/10 seconds in longitude along its orbit and
rotates at 15" per second. The latter number is important if you
use unguided photographs. The time is nedded to shift the measured
positions relative to the beginning or end time of the exposure.
If these are inaccurate, the whole measurement isn't very helpful.
Best wishes, Rainer
--
Rainer Arlt -- Astrophysikalisches Institut Potsdam -- www.aipdot de
Visual Commission - International Meteor Organization -- www.imodot net
rarlt@aipdot de -- phone: +49-331-7499-533 -- fax: +49-331-7499-526
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