[Prev][Next][Index][Thread]
Re: (meteorobs) Fire ball
Hey, Stephanie, thanks for the report! Kim has done an able job (as always) of
answer your questions, but I did want to comment on one interesting aspect of
your report:
>a great fireball, magnitude -1 due north that lasted about 10
>seconds. It had a minimal tail and fell in a wavy pattern.
I've seen a "wavy pattern" as you describe under two very different sets of
circumstances: First, while watching on the peak nights of various major meteor
showers - in particular those with the highest relative velocities, such as the
Perseids and Leonids - I have seen meteors which appeared to have two trails at
once, braided in and out of one another!
This is a really lovely effect, but I had a great deal of difficulty explaining
it until I brought it to this list: Then Malcolm Currie and other readers here
explained to me that persistent TRAINS - the brief "afterimages" you frequently
see behind fast meteors - are in fact expanding, hollow CYLINDERS of gas.
This "braiding" I saw was thus due to high-altitude winds acting on the train,
and to the foreshortening effect of perspective (the same effect that causes the
"Ring" Nebula in Lyra to look like a ring instead of a shell, and also causes
clouds near the horizon to appear to "bunch up"). Basically, the column of gas
in the train gets compressed in some areas and expands rapidly in others, so one
ends up seeing what look like "parallel trains" entangling one another.
Another "wobbling" effect which I have observed *much* more frequently is likely
what you were seeing with this satellite (or VERY slow meteor) you saw: Watching
artificial satellites slowly drift across the night sky, I often see them appear
to "tumble". They move in a straight line, but with an ever so slight "weaving"
motion from side to side... I assume this is in fact due to my own biological
rhythms (heartbeat, pulse, breathing) In effect, it's a kind of "autohypnosis",
similar to the illusion that makes the moon appear to move in a contrarywise
direction when it's shining through fast-moving clouds. Or perhaps there is some
even MORE devious optical illusion at work in this case... Who knows?
Thanks again for posting, Stephanie: One of the most interesting things about
observing the night sky for me, and especially about watching meteors, is all
the questions it can present to you about our own human perception. :)
Clear skies!
Lew Gramer
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html
References: