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(meteorobs) Re: meteor notes NM
Don said :
>what appeared to be a meteor impact the earth...aprox 2:30 am local time..
> 350 degrees magnetic from palm desert, Calif. USA.....Unknown distance..
> I was on a mountain top, and it was just beyond the horizon... almost
>vertical descent...and as soon as it dipped beyond the horizon, an impressive
>greenish glowing dome appeared for about a second...poss two...then
>vanished....(? poss. sporadic).. was so in awe of what we saw...
>
This was an excellent observation of a fireball continuing on below the
horizon. It created its own bit of "twilight." No guarantee of it
producing meteorites.
The most unusual situation I've had like that was in 1973 July from the
Florida Keys. A -8 Alpha Capricornid went below the western horizon which
had some cirrus present. I saw the Earth's shadow cast by the meteor flip
up into the sky projected onto the cirrus layer. Looked like a hand-held
fan being raised. The whole shadow event took less than a second.
From George and Steve:
>Hi, George:
>
>>Picture a tiny, hazy, fairly slow patch of blueish-white appearing and
>>disappearing at regular intervals as it crawls across a section of sky.
>
>>I assume you aren't describing a satellite here?
>
>It was many years ago, so I can't be sure. It might've been one
>re-entering the atmosphere and burning up, but would a satellite be able
>to withstand 15-20 seconds of friction and heat while skipping, with
>each visible skip lasting approximately 1.5 seconds? I thought it was a
>meteor at the time.
>
>Steve Sutton
Sounds very much like a tumbling satellite to me as well. If it were
reentering the atmosphere, I would expect an intense orange color with
heavy fragmenting. My longest convincing meteor was 15 seconds. I have
several in the 10-second range, usually with irregular variations in
magnitude. Long ones can sputter along, give small bursts in brightness, or
go out completely and reignite.
I have never seen a meteor convince me that it "skipped off the atmosphere."
Objects below some given size ought not be able to do that -- the drag would
finish them off. But the pair of fireballs in one evening over the western
U.S. last winter was interpreted by one researcher as being from just one
meteoroid. It hit the atmosphere tangentially the first time (I don't
consider that a skip-off ; there just wasn't any projected impact point),
then made a full earth orbit and reentered a second time further west. This
was discussed on meteorobs at the time.
The concept of possible skipping off is well illustrated by the return of
Apollo capsules from the moon. The blunt end of the capsule could behave
like a flat rock on water if the approach were right. Could a meteoroid,
with an irregular surface, accomplish the same feat?
From Bob:
> see the Milky Way as a greenish band of clouds and a sky
>filled with so many stars that constellations are hard to define.
I have to plug H.A. Rey's book again on this one. Experienced meteor
observers should not be in this situation ! The Rey method makes the
constellations jump out at you in a dark sky. An S&T reviewer ages ago
criticized the book for using too many faint stars, thus rendering it less
useful in city locations.
Several observers report years of observing without seeing a -15m fireball.
The same is true for me : two -12's and two -10's are my best in 37 years.
Overdoing it is common with certain individuals, esp. Povenmire who has seen
several -12's to -18's within a single year, and has many such events in his
life. As mentioned previously, he calls every meteor we ever saw jointly as
2 magnitudes brighter than me.
I did have a little luck in my first year. About the 300th meteor of my
life was a spectacular -8 with much fragmenting, 5:30 AM on 1960 Nov 26/27.
How could I forget the exact time of something like that? Thinking about it
years later, it must have been a Taurid.
Most Florida mosquitoes don't go for altitude. Observing with Povenmire
east of Orlando one night in 1974, we went to a site that had a 40-foot
tower platform. Climbing up there kept us bug-free. Even 10 feet up will
get you above almost all of them. In the 70's the best observing site I
ever experienced was on the old Bahia Honda Bridge in the Keys. The bridge
was 50 feet high, all but one night were bug-free, temperatures were balmy
(latitude 24.8N), and the sky was LM7.5 routinely. It's easy to get
spoiled after that. There was one particular night when the mosquitoes
swarmed the channel and got us on the bridge. The Fort Myers area has 68
different species of mosquitoes, and I doubt if any of them are in common
with the ones that bother Bob. I'm thinking, if they are already 4000 feet
up, they might as well go up 10 more feet and visit Bob.
There were 50 meteorobs messages yesterday, a quarter of which were
Jonathan's. I thought we had brought this type of activity under control a
few weeks ago, but it resurfaced big time. Hopefully it will improve. Both
AMS Jims expressed themselves well on the need to read books first, then get
with the rest of us. Admittedly the general astronomy textbooks are very
skimpy on meteors. In a book of 300 or more pages I usually see only 2 pages
about meteors complete with an aging list of showers. But there are always
encyclopedias and magazine articles to help fill in.
The constant flood of mail inquiries the AMS receives has many young people
who also could read books for the same information. It must be more
exciting to get mail from an organization. Prominent amateurs, and other
astronomy groups, I am sure, have the same problem.
Sometimes we witness an outbreak of the sillies amongst a few of the
contributors, adding to the e-mail volume as well. A little humor in a
larger post is no problem ; I do this myself. One-liners ought to go privately.
Norman
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