Expert: Tom Whiting - 1/14/2008

Question
QUESTION: Hi. Tonight me and two of my friends were stargazing and saw about 5 shooting stars scattered across the sky about 3 minutes apart. Suddenly the ENTIRE sky, I'm talking from as far as we could see in every direction and above us, flashed a greeny blue colour for about half a second. We could not see any stars or clouds or ANYTHING but the bright greeny blue flash in the sky, which seemed as if the sky itself were glowing. It was almost like lightning but DEFINETLY not and a complete different colour. The sky was perfectly clear and we could see every star before and after the flash. I then turned around to where i thought the bluey green hue was fading towards (at an very fast rate, like a second) and saw what looked exactly like a comet moving at a fair speed, but the comet faded quickly (about 7 seconds till we couldn't even see the trail) and it seemed as if the greeny blue light in the sky was receding towards it, like the light came out of it and retreated back in. as ridiculous as this may sound. We were not on any drugs or under the influence of alcohol. It was at exactly the minute of 12:45am and we live in the north island of New Zealand. We searched the internet and the only results we found are a green flash that can occur above the sun at sunset or sunrise and it was definetly nowhere near either and looked nothing like the pictures as it covered the whole sky. We are completely stunned and were left a little unnerved by this phenomenon. Can you shed any light on this occurance? (terrible pun) Thanks alot. Please explain this! :)

ANSWER: Hi Leigh,
Yes I can, because a very similar thing has happened to
me also.  What you saw (or didn't see, because you all
were facing in the wrong direction) was probably one of the best meteors of your life, a fireball or bolide. Probably a bolide, as the initial light was the main meteor exploding (behind where you were observing) as it hit the top of our atmosphere. It was down low near the horizon to begin with, and initially would have been nearly as bright as the full moon for an instant, as it hit the atmosphere. After about a half-second, after explosion, the meteor's remains proceded down closer to the horizon (what you call a "moving comet for 7 seconds")..at least you got to see the remaining meteor chunk for the last few seconds of it's short life. This was the remaining large particle or chunk, still burning in the atmosphere, and moving away from you giving off sparks and a trail, but not nearly as bright as the initial explosion. Thus the glow was receding back toward the remaining chunk of meteor.  The greenish-blue colour came from the incandescent copper and cobalt, copper burning green and cobalt burning blue.  (In my case, it was reddish-yellow with iron burning red, and probably magnesium burning yellow). So while it was a spectacular and un-nerving event, that's exactly what it was.

You gave an excellent description here and that's how I
can explain it due to your fine explanation...But
let's correct some terminology here.  First avoid the
term "shooting or falling star"....there is no association with stars here. They are called meteors, and if they
happen to hit the ground they are called meteorites. Before
they hit the atmosphere, they are called meteoroids.

Second, a real comet doesn't move like that, a real comet moves very slowly across the sky, like 1 degree every 24 hours, or equal to the apparent diameter of 2 full moons.... (The moon's diameter is 1/2 degree across)and comets are deep space objects and not in our atmosphere like your object was.  But I knew what you meant when you said "comet-like" because that is the typical impression of a new observers opinion of a "comet". Real comets last for weeks in the sky...up north here, we've been following Comet Holmes up in Perseus since late October.  What you refer to as a "comet" was the last 7 seconds of the event and was simply the remains of the bolide, leaving a fine trail of sparks.  
Several questions remain however....was there any afterglow
of the trail, like for 30 seconds or one minute?
And after the bright light in the sky, did you hear any
rumble or thunder-like sound after several minutes?
A lot of times with a bolide up say, 60 miles high
observers actually hear the explosion as a low rumble, like
thunder, in about 5 minutes. (60 miles high is an average
height, times speed of sound, 5 seconds per mile, gives
300 seconds, or about 5 minutes). So, was there any after-sound later on???  Always check for that with a bolide. It's just too bad you all weren't facing in that direction...I missed my fine one too, and only got to see the glowing after-trail for about 60 seconds.  In other cases, sometimes they light up the entire landscape for about 1/2 second, as if someone has taken a camera flash picture behind you.
But keep watching the night sky, and perhaps you'll get
to see another one.  Oh, you might also want to inform
your local newspaper or TV station of the time and the
event as it's possible that other people were out observing
and thinking the same thing you are, and that way you
can get together and compare notes.

Oh, just for size reference on meteors, the typical meteor
is grain of sand size, and a nice fireball or bolide is
walnut or tennis-ball size, so that's probably the size
of the chunk of space debris you saw hit the atmosphere,
and it probably didn't hit the ground because the flight
you gave sounds like it was coming in at a very shallow
(flat) angle...so don't bother looking for any remaining
meteorite. Oh, you might also want to get on the USA
NORAD (North American Aerospace Defense Command) website
as NORAD has satellites that keep track of these bolides
(as they appear on satellite views as large missile launches or illegal nuclear test explosions).  Another fine
website is www.spaceweather.com to report your event.
Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA  USA

FOLLOW UP:
Oh, you may also want to take a minute to fill out a report form on the internet to the International Meteor Organization, to report your bolide or fireball, at
http://www.imo.net/fireball/observations
Clear Skies,
Tom Whiting
Erie, PA


---------- FOLLOW-UP ----------

QUESTION: As a reply to your questions yes there was an after glow on the trail and we could see the trail for about 30 seconds. and We didnt hear a rumble but we were also being rather loud about 5 minutes after seeing it. Thanks again.

Answer
Hi Leigh,
Thanks for the nice comments and ratings.
Yes, well that 30 second after-trail confirms my explanation, as generally it's only the very bright fireballs and bolides that leave an afterglow-trail that long.

Well, don't be too hard on the "local observatory" especially if they are professional astronomers.  Ironically, the pro's don't know the night sky as well as
us amateurs, because they sit in a control room and punch
in the numbers, and the telescope does all the work. With
us amateurs, we have to know the night sky and physically
move our scopes, so we have to know the night sky as we
are outside all the time, and not in a nice warm, comfortable control room.  Well, next time, try to listen
for some kind of sound about 5 minutes later, so now you
know to do so.
And if you ever need additional help, feel free to contact
me directly at bwhiting@velocity.net
Clear Skies,
Tom Whiting  (retired USAF)
Erie, PA USA