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Re: (meteorobs) Some Central Texas Ursids
Follow-up to my earlier message.
I wish I'd have made it to begin observing before 6:00 UTC.
I don't yet know how to calculate ZHR. For the 10-minute
period 7:25-7:35 UTC I saw 4 Ursids. The radiant (very
near +4.3 star 5 UMi, I think) was about 25 degrees above
horizon at this time. From an IMO table regarding the
relation of radiant height to ZHR:
http://www.amsmeteors.org/imo-mirror/visual/major01.html#when
-- if I understand correctly -- if the radiant is 30
degrees up, the observed rate is reduced to about 1/2 of
ZHR. So may I infer a doubled raw rate of eight meteors
in ten minutes if radiant had been at zenith? That would
be 48 per hour, which I believe is high for URS (although
I would not assume that one ten-minute period is by any
means a statistically significant indicator). I don't
know what the LM correction is if my LM was say +5.5 or
+6.0 when ZHR uses +6.5.
Footnotes:
Considering my seemingly high counts, maybe I underestimated
LM? Maybe it was better than +5.5, although I doubt it was
better than +6.0. (Obviously this is a skill I very much
need to develop!)
I left out one meteor because I wasn't sure if it was an
Ursid or not. So my count *should* have been either 26 URS
and 29 SPO, or 25 URS and 30 SPO. (I wonder why was my
sporadic count so high -- about 15 per hour, and in the wee
hours rather than the hours just before dawn?)
The humidity was low; there was very little dew for a nearly
calm, very cool night.
I'm very nearsighted with astigmatism and wear glasses.
Concluding remark: Even though I didn't see hordes of
meteors, I'm very glad that the weather permitted and that
I did go out and see my first Ursids (and possibly even a
bit of an outburst)!
Ed Cannon - ecannon@mail.utexasdot edu - Austin, Texas, USA
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