[Prev][Next][Index][Thread]
(meteorobs) Excerpts from "CCNet, 7 December 1999"
Three interesting contributions from this issue! Note especially
the summary of the NASA Express Web site on the Geminids... BTW,
if you do observe the Geminids this year, please consider using
the IMO or similar recording methods...
Lew Gramer
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 7 December 1999
Date: Tue, 7 Dec 1999 10:51:23 -0500 (EST)
CCNet, 7 December 1999
--------------------------------
[...]
(3) METEOR SHAKES THINGS UP
MSNBC, 6 December 1999
(4) ON THE ORBIT OF THE TUNGUSKA COSMIC BODY ACCORDING=20
TO BRONSHTEN
Luigi Foschini <foschini@tesre.bo.cnrdot it>=20
[...]
(6) PHAETHON AND THE GEMINID METEORS
NASA Science News, 7 November 1999=20
[...]
=======================================================
(3) METEOR SHAKES THINGS UP
>From MSNBC, 6 December 1999
http://www.msnbc.com/local/wvtm/139588.asp
BIRMINGHAM, December 6, 1999 =96 A meteor streaking through the sky =
early=20
Sunday morning, lit up the night in three states. Police dispatchers=20
were busy with hundreds of phone calls about the mysterious light and=20
loud boom that followed.=20
=20
A black and white surveillance camera caught Sunday=92s mysterious =
light=20
on tape. A pitch black street gets lighter, then bright as day. As=20
quickly as it happens, everything returns to darkness.
"It was so bright. It was brilliant and the most beautiful thing I=92ve =
ever seen. The light shone through the clouds about ten seconds. It=92s =
beautiful blue and white light, and I=92d say it could be seen from=20
hundreds of miles around," said Bessemer police officer Stephen=20
Williams.
Williams was patrolling 9th Ave. around 4 a.m. when he saw the dim=20
light in the sky get brighter. He said it looked like someone was=20
turning up a dimmer switch. At one point, the light was as bright as=20
day. He was relieved to find out about 10 other patrol officers had=20
seen it too.
"Somebody keyed up the radio and said =91Did you guys see that?=92 It =
was=20
pretty amazing, and we were all radioing back and forth as to what we=20
pondered it might be. We got together a little later, and we were all=20
still shaking,=94 said Williams.
About 10 seconds after the light disappeared, Williams said he heard a=20
loud noise, similar to a sonic boom. "We did get a lot of calls,=20
apparently the light shone bright enough to light up the inside of=20
houses. The boom was very loud and it shook some people=92s windows,=94 =
said Williams.
Brad Young was with friends in Albertville about 75 miles away when he=20
saw the mysterious and light and heard the boom.
"It was like a white ball of fire flying through the sky and had a big=20
long tail behind it, and then a couple of seconds later it like bang,=20
made a loud bang, and then it was gone," said Young.
=20
DON=92T EXPECT A CRATER
Georgia astronomer Dave Dundee has been fielding questions about the=20
sightings. He believes it was caused by a meteor. That=92s defined as a =
solid body from outer space which glows with heat generated by friction =
as it enters the Earth=92s atmosphere.
Roswitha Becker with Birmingham Southern=92s planetarium says what=20
happened Sunday night wasn=92t too far out of the ordinary. "The Earth =
is=20
bombarded by thousands of debris on a daily basis, of space dust that=20
just falls on the Earth," said Becker.
Rocks and debris travel so fast, they leave glowing tunnels of hot air=20
in the sky. "It=92s friction. They=92re hitting the air, and they heat =
up=20
air molecules very hot next to them... It=92s a florescent sort of
effect," said planetarium worker Kurt Bachmann.
Scientists say, despite the loud boom which followed Sunday=92s bright=20
light, more than likely nothing ever hit the ground. National Weather=20
Service expert Kevin Pence says shooting stars are a lot like what we=20
see and hear in a thunderstorm.
"You know, the lightening first, and then the rapid explosion or=20
expansion of a channel of air, creates sound waves," said Pence.
Copyright 1999, MSNBC
=======================================================
(4) ON THE ORBIT OF THE TUNGUSKA COSMIC BODY ACCORDING=20
TO BRONSHTEN
>From Luigi Foschini <foschini@tesre.bo.cnrdot it>=20
Dear Benny,
The two recently published papers by Bronshten about the Tunguska=20
Cosmic Body (TCB), and that you cited in recent issues of CCNet, raised
several questions. I would like to add some notes to the debate.=20
I have read the recent paper by Bronshten about possible constraints to
the possible orbit of the TCB (V.A. Bronshten: "Trajectory and orbit of
the Tunguska meteorite revisited". Meteoritics and Planetary Sciences=20
34, (1999), A137-A143). I think that Bronshten used the principle "post
hoc, ergo propter hoc": indeed, he started considering geocentric=20
speeds of the TCB from 25 to 40 km/s and he deduced that cometary=20
orbits are consistent with trajectory data. However, an asteroid with=20
speed higher than or equal to 25 km/s is quite rare: it is known that=20
the typical NEO speed is around 16 km/s. Therefore, when Bronshten=20
selected the speed range, he implicitly considered typical cometary=20
bodies. It is then obvious that he obtained that TCB was a comet.=20
Cheers,
Luigi
=======================================================
(6)PHAETHON AND THE GEMINID METEORS
>From NASA Science News, 7 November 1999=20
http://science.nasadot gov/newhome/headlines/ast06dec99_1.htm
Great Geminids!
On December 13 and 14, 1999, fragments of the mysterious asteroid 3200=20
Phaethon will strike Earth's atmosphere and produce a beautiful sky=20
show.
December 7, 1999: The 1999 Leonid meteor storm was a rare treat for=20
many skywatchers in Europe and the Middle East, but a bit disappointing =
in other parts of the world. If you missed the Leonid display because=20
of poor weather, or perhaps because you live in the wrong place,=20
there's still one more chance in 1999 to see a good meteor shower: the=20
Geminids.=20
The shower officially begins on December 7th, but it doesn't peak until
the morning of the 14th around 3 a.m. PST (1100 UT). Unlike the=20
Leonids, the Geminid's broad maximum lasts nearly a full day, so=20
observers around the globe have a good chance to see the show. At its=20
peak the Geminids could produce as many as one shooting star every 30=20
seconds.=20
For observing tips see www.Geminids.com
Most well known meteor showers, like the Perseids and Leonids, are old.
They've been observed for hundreds or even thousands of years. The=20
earliest record of a modern-day meteor shower is probably a notation in =
Chinese annals dated 36 AD, regarding the Perseids, where it is said=20
that "more than 100 meteors flew thither in the morning." [ref.]=20
The Geminids are a different story. The first Geminid meteors suddenly
appeared in the mid-1800's. Those early showers were unimpressive,=20
boasting a mere 10-20 shooting stars per hour. Since then, however, the
Geminids have grown in intensity until today it is one of the most=20
spectacular annual showers. In 1998 observers counted as many as 140=20
per hour (zenithal hourly rate). Sky-watchers with clear skies should=20
see at least that many this year if the Geminids continue to intensify. =
After the discovery of the Geminids in 1862 astronomers began searching =
for the parent comet. Most meteor showers result from debris that that=20
boils off a comet's nucleus when it passes close to the sun. This=20
debris orbits the sun along with the comet, forming a thin, elongated=20
stream of meteoroids that become shooting stars when they hit Earth's=20
atmosphere.=20
Years of searching proved to no avail until finally, in 1983, NASA's=20
Infrared Astronomical Satellite discovered a curious object moving in=20
the same orbit as the Geminid meteoroid stream. The orbital match was=20
so good that it had to be the source of the debris, but to the surprise =
of many it wasn't a comet. The source of the Geminids was apparently a=20
rocky asteroid.=20
3200 Phaethon, as the asteroid is now known, is in a highly elliptical=20
1.4 year orbit that brings it within 0.15 AU (astronomical units) of=20
the Sun. It made its closest recent approach to Earth in December 1997=20
when it passed within 0.31 AU of our planet.=20
But how does an asteroid produce a meteoroid debris stream? Comets do=20
it easily whenever they pass close enough to the sun to heat their=20
frozen nucleus. Tiny bits of ice and dust naturally bubble away into=20
interplanetary space. Rocky asteroids are made of tougher stuff,=20
however, so it is unclear how bits of 3200 Phaethon would break or boil =
off to form a meteoroid stream.=20
One of the earliest ideas was that Phaethon might occasionally collide=20
with other asteroids. Collisions would create a stream of pulverized=20
rocks that would account for the Geminids meteor shower. Phaethon's=20
orbit passes through the asteroid belt just beyond Mars, so at first=20
this hypothesis seemed likely, but more detailed studies disagree. The=20
orbits of individual Geminid meteoroids are not consistent with the=20
idea that they broke free while in the asteroid belt. Instead, they=20
appear to have crumbled away when Phaethon was closer to the Sun. In=20
this respect Phaethon is behaving like a comet.=20
So, which is it?
Is Phaethon a comet or an asteroid?=20
There are arguments in favor of both. Phaethon's spectra look like=20
those of a rocky asteroid, but its orbit is similar to that of a comet. =
When Phaethon passes by the sun it doesn't develop a cometary tail, but =
bits and pieces do break off to form the Geminid meteoroids. By=20
studying photographic records of fireballs, scientists have estimated=20
the density of the Geminid meteoroids to be between 1 and 2 gm/cc.=20
That's less dense than typical asteroid material (3 gm/cc), but several =
times denser than cometary dust flakes (0.3 gm/cc). Many astronomers=20
now believe that Phaethon is an extinct or dormant comet that has=20
accumulated a thick crust of interplanetary dust grains. Phaethon's=20
thick mantle gives it the outward appearance of an asteroid, but=20
underneath lies the nucleus of a comet.=20
The origin of the Geminids may not be fully understood until future=20
space travelers pay a visit to the asteroid-comet 3200 Phaethon. Until=20
then we can still enjoy the sky show and savor the mystery of the=20
enigmatic Geminids.=20
----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To subscribe/unsubscribe,=20
please contact the moderator Benny J Peiser <b.j.peiser@livjm.acdot uk>.=20
Information circulated on this network is for scholarly and=20
educational use only. The attached information may not be copied or=20
reproduced for any other purposes without prior permission of the=20
copyright holders. The fully indexed archive of the CCNet, from=20
February 1997 on, can be found at
http://abob.libs.ugadot edu/bobk/cccmenu.html
------- End of Forwarded Message
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html