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View Full Version : What happened here? [Australia - comet? asteroid?]



Juran
2011-May-31, 12:08 AM
Thime and Date: Approximately 10-15pm Sunday May 29
Where: High in the north eastern sky
Viewed from: A small bay 30 km north of Cairns in far north Queensland, Australia.

What I presume was an Asteroid plunged down the north eastern sky. It was extremely bright and its tail trailed a long way behind it. Its fall continued for some moments until it suddenly disappeared, tail and all. A remarkable and memorable sighting but, totally enexpectedly, it reappeared a fraction later and continued its fall as if it had passed behind something which of course is riddiculous because if it had passed behind something then that something must have been huge not to mention invisible to the naked eye. So I am thinking there has to be reason why an asteroid, comet, whatever would suddenly 'go out' and a fraction later (maybe a half a second) come 'back on' again. Any ideas?

jfribrg
2011-May-31, 02:34 AM
maybe it broke apart in two distinct phases. maybe the volatiles (ice and gasses) burned up followed by a period where the rock heated up withouth anything burning, and finally the rocky part burned up.

Middenrat
2011-May-31, 02:42 AM
Hi Juran, I wish I'd seen that, Its sounds like you're describing a fireball or 'bolide' all right, which would be a chunk of rock smaller than an asteroid or comet - maybe tabletop-sized. These are encountered at very large velocities, sevevral miles per second, and if the angle is just right they can skip through the top layer of our atmosphere like a stone over water, with the blazing tail produced when friction is greatest, then fading out as the bolide bounces to a higher altitude, then drops back down into the thicker air again, etc.

astromark
2011-May-31, 03:26 AM
As you described it.. I like Middenrat's skipping bolide... or it was just two parts of something burning up..
It would or could look like you said.

Juran
2011-Jun-01, 05:50 AM
Yes that makes sense. It was very bright suggesting that It was not that far out so I suspect that the atmosphere played a part. Thanks.

Jeff Root
2011-Jun-01, 05:38 PM
The most likely reason for a fireball to disappear and then
reappear a fraction of a second later is that it went behind
a cloud. If it skipped out of the atmosphere far enough to
stop glowing, it would take at least many seconds to fall
back to a level where it would glow again. It could only
fall again if it had lost enough speed to be moving at less
than escape speed.

Another possibility is that the object was burning up very
unevenly, so became much dimmer for a fraction of a
second. That might happen with a meteoroid composed
of different materials, or a man-made satellite.

-- Jeff, in Minneapolis

NEOWatcher
2011-Jun-01, 06:16 PM
If it skipped out of the atmosphere far enough to
stop glowing...
Isn't it the atmosphere being compressed that's glowing first?

Jeff Root
2011-Jun-01, 07:57 PM
Yes, same difference. They both glow. I don't know that one
starts glowing first or that one glows brighter than the other, but
the air would have a much larger cross-section so more light
would come from the glowing air than from the glowing object.

-- Jeff, in Minneapolis

NEOWatcher
2011-Jun-01, 08:11 PM
Yes, same difference. They both glow.
My aim was to point out that it's not really the object that we are seeing.
Considering the temperature of the incomming object, and the size of its heat sink, I can't see how the object can start to glow quickly enough for it to have any noticeable effect on brightness.

Of course, I don't have any numbers to back that up, I'm going mostly by observation.

slang
2011-Jun-02, 12:17 AM
Late... tired... try http://www.imo.net/ , International Meteor Organization. Maybe they have reports about this one.

Juran
2011-Jun-02, 01:10 AM
It was a magnificently clear night sky which made the sighting the more spectacular, certainly no cloud.
Take up a felt pen and run it idly down the length of a blank A4. Suddenly stop as you enter the lower quarter, take the felt away from the paper, leave a 3cm gape and then continue the idle line to the bottom. This is what I saw. The tail had width and it did not taper off. It, whatever it was, had no noticeable head but of course it must have... unless it was a band or streak of light, although it didn't behave like lightning I suppose it is a possibility. Gut feeling says no but I guess there is no science in gut feelings.