Zenithal attraction, and beautiful sloooow meteors (was Re:(meteorobs) June Bootids - Call for observations)

Kim Youmans ksyo at bellsouth.net
Tue Jun 22 16:58:49 EDT 2004


Ditto and bravo for the heads-up on the beauty of slow meteors, Lew.  At the
risk of changing this forum into a chat-room (in addition to getting
slightly off-topic) I'd like to re-share the most exciting meteor I've seen
yet this year (and one I will never forget...)   This turtle/snail was back
in Febuary....

  ...I arched back and looked up, and the show began.  Perhaps this slow
moving meteor had been at 0 magnitude
when I first looked up and saw it, in southern Draco, but as it passed
through
Corona Borealis -- moving *very, very* slowly -- it settled into a +1
magnitude
and for the rest of its flight, it never varying from that. I got a great
view of it,
as it crawled across the sky, with a one-to-three degree wake, and a very
distinct head.  As it continued, my jaw began to drop -- this one wasn't
about to fade out!  As it, finally, approached western Scorpio, it
seemed to slow just a bit and the tail/wake shortened until, when it
reached Lupus, it was a point meteor sitting motionless in that
constellation!  An amazing sight! It hung, an univited guest star, in Lupus
for another
three seconds at least.  All in all, I'd guess the meteor lasted a good
12-15 seconds!!! I observed it travel at least 90 degrees.

Well, thanks for letting me re-live the excitement that single, slow,
not-too-bright meteor can sometimes bring.....

Kim Y.


----- Original Message -----
From: Lewis J. Gramer <lgramer at upstream.net>
To: 'Global Meteor Observing Forum' <meteorobs at meteorobs.org>
Sent: Tuesday, June 22, 2004 4:51 PM
Subject: Zenithal attraction, and beautiful sloooow meteors (was
Re:(meteorobs) June Bootids - Call for observations)


> Bob Lunsford wrote:
> > >Note that the apparent radiant is always shifted towards
> > >the zenith by a few degrees. This is because of the slow
> > >speed of the June Bootids.
>
> And Richard Kramer then responded:
> > This is a very interesting point. The reason for it alludes
> > me. I wonder if someone would be kind enough to explain
> > this subtlety.
>
> Richard, the reason for this "zenithal attraction" is simply
> the Earth's gravitational pull!
>
> Basically, imagine a meteoroid coming in at a certain angle
> relative to your local horizon. Now imagine what happens as
> it nears the earth - just prior to its "fiery plunge" into
> the atmosphere. Remember, gravity will gradually deflect the
> meteor's path along a parabolic track toward Earth's center.
>
> What's the result of this deflection, from the point of view
> of an observer on the ground? The meteor's "radiant point" -
> an imaginary spot on the celestial sphere that its apparent
> path can be traced back to - will tend to shift toward your
> local zenith! And of course, vector arithmetic (folks might
> remember those fun diagrams from high school physics!) will
> tell you that, the SLOWER the meteor is relative to gravity's
> accelerating effect, the more NOTICEABLE this deflection is.
>
> (All meteors are subject to this "Zenithal attraction", of
> course: but meteors from most showers are fast enough that
> it isn't too significant while observing. But as Rainer and
> Bob Lunsford mention, the June Bootids - just like the Kappa
> Cygnids later on this Summer - are a rare, slow exception!)
>
>
> And by the way, even if you only get to see one or two JBOs
> tonight, folks, remember - meteors *this* slow can really be
> stunning sights! Assuming Bob's maximum of 10 degrees/second,
> that means the average June Bootid well away from the radiant
> might last a full half-second or more. That's enough time to
> yell, "Look at that!" - and actually have someone get to turn
> their head in time to see your meteor! :)
>
>
> Clear skies,
> Lew
>
>
>
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