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Cambridge-Conference Digest - January 21, 1998

CAMBRIDGE-CONFERENCE DIGEST, 21 January 1998
--------------------------------------------

				"The upper air burst into life! 
				And a hundred fire-flags sheen, 
				To and fro they were hurried about! 
				And to and fro, and in and out, 
				The wan stars danced between"

				(Samuel Taylor Coleridge)


(1) COLORADO BOLIDE UNRELATED TO COMET HALL-BOPP

(2) DID LEONID METEOR SHOWER OF 1797 INSPIRE SAMUEL TAYLOR COLERIDGE?

(3) IT CAME FROM THE SKIES ....

(4) WHY ARE THERE LEONID METEOR STORMS BUT NO REGULAR ANNUAL 
    ACTIVITY?

(5) NEAR SPACECRAFT ON ITS WAY TO RENDEVOUZ WITH EROS

(6) NEAR S/C EPHEMERIDES AVAILABLE ON WORLD WIBE WEB

======================================================================
(1) COLORADO BOLIDE UNRELATED TO COMET HALL-BOPP

From: Graeme Waddington 
 
Re.  IS THE COLORADO BOLIDE A FRAGMENT OF HALE-BOPP?
 
Benny,
 
Further to my note of yesterday I have now been able to check the 
details and find that the mooted Hale-Boppid radiant would have 
actually been just BELOW the north-eastern horizon as seen from 
Denver at the quoted time of observation: The radiant would not have 
risen above the Denver horizon until 25 minutes later. The Colorado 
bolide therefore had no connection with comet Hale-Bopp.
 
Graeme Waddington
MRC Magnetic Resonance Spectroscopy Unit
John Radcliffe Hospital
Oxford

==========================================================================
(2) DID LEONID METEOR SHOWER OF 1797 INSPIRE SAMUEL TAYLOR COLERIDGE?

From: Phil Burns 

The article at
 
   http://news.bbc.co.uk:80/hi/english/sci/tech/newsid_48000/48756.stm
 
discusses Duncan Steel's suggestion that portions of Samuel Taylor
Coleridge's 'Rime of the Ancient Mariner' reflect his observation
of the Leonid meteor shower of 1797.
 
An article end-note also mentions that the largest crater formed by a 
meteorite is Coon Butte in Arizona.  I suppose one might claim this is 
the largest terrestrial crater -proven- to be of impact origin because 
meteoritic material was found in the vicinity.
 
 -- Phil "Pib" Burns
    Northwestern University, Evanston, IL.  USA
    pib@nwu.edu
    http://pibweb.it.nwu.edu/~pib/

======================================================================
(3) IT CAME FROM THE SKIES ....

From: 
http://news.bbc.co.uk:80/hi/english/sci/tech/newsid_48000/48756.stm

It came from the skies ...

Coleridge may have been inspired by a celestial display

Meteors have been blamed for everything from defeat in battle to UFO 
sightings to the huge Tunguska explosion in Siberia in 1908. Now they 
have been credited with inspiring some of Samuel Taylor Coleridge's 
most famous lines: 

The upper air burst into life! 
And a hundred fire-flags sheen, 
To and fro they were hurried about! 
And to and fro, and in and out, 
The wan stars danced between 

And the coming wind did roar more loud, 
And the sails did sigh like sedge; 
And the rain poured down from one black cloud; 
The Moon was at its edge 

Literary scholars have long been intrigued by the description of a 
storm of light above the sea from the Rime of the Ancient Mariner. Some 
thought it was a work of imagination, possibly fuelled by narcotics. 

However an astronomer in Australia says Coleridge was actually 
describing a meteor shower that he witnessed 200 years ago while 
walking along the Somerset coast with William and Dorothy Wordsworth. 

Dr Duncan Steele says that the threesome observed the Leonid
meteor shower - caused by the Tempel-Tuttle comet - back in 1797
and were so impressed by the celestial display that they set off on a 
rather long walk to the coast to get a better view. 

Dr Steele says Coleridge's words mirror the real event, albeit in a 
rather poetic way: "'The upper air burst into life' really sounds like 
a meteor shower stretching across the sky, with lots of shooting stars 
all at the same time."

However, he says the Leonid showers have also had an adverse effect on 
people. Records show that when the meteors appeared in 1833 people hid 
under their beds in fear of the Second Coming and Judgement Day. 

The Tempel-Tuttle comet comes around every 33 years. As it returns to 
the inner solar system it brings with it a dense swarm of minute dust 
particles, which enter the Earth's atmosphere at up to 72km/s, lighting 
up the sky.

The display has been seen only half a dozen times since Coleridge's 
day. It is due to recur later this year, allowing Coleridge fans to get 
a better insight into what the Mariner - and the poet himself - might 
have seen. 

Dr Steele points out that although understanding is much greater than 
in Coleridge's day, the event brings with it new hazards. 

He explains that there are no Space Shuttle launches due in November 
this year because of the danger of caused a dense flux of meteoroids in 
space - the speed is such that even something the size of a pea could
cause catastrophic damage to a spacecraft. 

Meteor facts 

Around 40 tonnes of space debris land on the Earth every year, but much 
more is burnt up in the atmosphere. 

There are an estimated 100,000 objects wider than a kilometre floating 
around the solar system close enough to pose a threat to the Earth. 

At least 100 space rocks large enough to cause global devastation are 
known to intersect the Earth's orbit. 

Some 500 'big impact events' have occurred in the last 540 million 
years. 

In November 1996, a five kilometre long asteroid passed around 5 
million kilometres from Earth. If it had hit, it could have wiped out 
the human race. 

A search for a huge meteorite in Greenland was sparked off by dazzling 
flashes equivalent to a nuclear explosion and seismic signals in 
December, but was hampered by thick snow and winter darkness. 
Scientists believe the object may have weighed 50 tonnes and have been 
travelling at about 10,000 km/h. 

The largest crater formed by a meteorite is Coon Butte in Arizona, 
which has a diameter of more than 1,000m and a depth of just under 
200m. It is thought to have been caused by an iron-nickel mass of 
around two million tonnes. 

The largest intact meteorite found on Earth was nearly 3 metres long 
and weighed around 60 tonnes. It was found in Namibia in 1920. 

A meteorite is thought to have caused the extinction of the dinosaurs 
65 million years ago when it exploded with a force five billion times 
that of the Hiroshima bomb in the Yucatan peninsula in Mexico, leaving 
a crater at least 100 kilometres across. 

A fictional meteor shower caused widespread blindness in John Wyndham's 
The Day of the Triffids..

=======================================================================
(4) WHY ARE THERE LEONID METEOR STORMS BUT NO REGULAR ANNUAL 
    ACTIVITY?

I. P. Williams: The Leonid meteor shower: why are there storms but no 
regular annual activity? MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL 
SOCIETY, 1997, Vol.292, No.1, pp.L37-L40

UNIVERSITY OF LONDON, QUEEN MARY & WESTFIELD COLLEGE, ASTRONOMY UNIT, 
MILE END RD, LONDON E1 4NS, ENGLAND

The Leonid meteor shower is the most famous meteor shower of all 
time. The main characteristics of the stream are well known, being 
very spectacular displays of meteors occurring on numerous occasions 
when the parent comet, 55P/Tempel-Tuttle, is close to perihelion. 
Since there is a perihelion passage of the comet due on 1998 February 
28, it is a topic of intense interest to predict whether or not a 
spectacular display will be seen in 1998 or 1999. It is not, however, 
the primary purpose of this presentation to make predictions 
regarding this event, but rather to address an equally interesting 
problem related to the Leonids, which is: why do we not see even a 
moderate display like those of the Orionids or the Geminids in years 
when the parent comet is far from perihelion? We suggest that the 
gravitational perturbations from the planet Uranus, resulting from a 
particular set of geometrical circumstances that have been present 
over the last two thousand years, but which will come to an end in AD 
2160, have been responsible.

========================================================================
(5) NEAR SPACECRAFT ON ITS WAY TO RENDEVOUZ WITH EROS

From: Ron Baalke 

Donald Savage
Headquarters, Washington, DC                      January 20, 1998
(Phone:  202/358-1547)
 
Helen Worth
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone:  301/953-5113)
 
RELEASE:  98-9
 
EARTH SWINGBY PUTS NEAR SPACECRAFT ON FINAL APPROACH TO EROS
 
NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft, built by The 
Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, 
MD, will become the first interplanetary spacecraft that can possibly 
be seen with the naked eye when it swings by Earth Jan. 22-23.  The 
spacecraft's solar panels will reflect the Sun's rays onto the Earth 
in a greeting as it flies by for an adjustment of its trajectory to 
correctly align the spacecraft for a rendezvous with asteroid 433 
Eros, its mission target.  
 
Launched Feb. 17, 1996, NEAR completed a flyby of the asteroid 
Mathilde in June 1997 and is now on its way back to Earth. Late 
Thursday, Jan. 22, the spacecraft will approach Earth over the 
Pacific Ocean traveling at about 20,000 mph. Because the United 
States will be in darkness as NEAR approaches, if there is no cloud 
cover, several geographic areas will be able to see the Sun 
reflecting off the spacecraft's solar panels, which will act as large 
mirrors.  These sunglints will be visible on the East Coast, Friday, 
Jan. 23, at about 1:30 a.m. EST and the West Coast at about 1:45 a.m. 
EST (Thursday, 10:45 p.m. PST). 
 
The spacecraft then swings around the Aleutian Islands and over 
Siberia before reaching its closest point to Earth, about 336 miles 
above Ahvaz in southwest Iran, Friday, Jan. 23, at 11:23 a.m. local 
time (2:23 a.m. EST), traveling at about 29,000 mph, its fastest 
speed for the swingby.  Although NEAR will be close to Earth at this 
time, daylight may obscure its image.  
 
The spacecraft then swings over Africa and on to Antarctica before 
pulling away from the Earth at a speed of about 15,000 mph. The 
swingby will have changed NEAR's trajectory to approximately 11 
degrees south of the Earth's ecliptic plane, the orbital path the 
Earth takes as it circles the Sun, and put the spacecraft on target 
for its Jan. 10, 1999, rendezvous with Eros. 
 
NEAR scientists and engineers are using the swingby as an opportunity 
to test performance and calibration of the spacecraft's six 
instruments and to practice coordinated multi-instrument observations 
of the type that will be used at Eros. 
 
The Multispectral Imager, a visible light camera that will help 
determine the physical characteristics of Eros, and the NEAR-Infrared 
Spectrograph, used to study surface minerals, will be calibrated by 
comparing their readings of geological features with proven 
measurements of the same areas. These instruments will also be used 
to take images of the Earth along the spacecraft's 
path. NEAR's Magnetometer will be calibrated by comparing swingby 
data with known measurements of the Earth's magnetic field. 
 
Other activities during the swingby will include using the 
X-Ray/Gamma-Ray Spectrometer to observe celestial gamma ray bursts 
and to collect data on gamma ray and X-ray backgrounds. These data 
are needed so scientists can better remove background impurities from 
the measurements to be made at Eros.  
 
NEAR is expected to capture its first images of Eros, a 25-mile-long 
near-Earth asteroid, a few months prior to the 100th anniversary of 
the asteroid's discovery on Aug. 13, 1898.  After reaching Eros, the 
spacecraft will start its orbit about 600 miles above the asteroid's 
surface, descending to 200 miles by February and coming as close as 
10 miles during its yearlong study. Scientists will thoroughly map 
Eros and will examine its surface composition and physical 
properties. On Feb. 6, 2000, the mission is expected to end with a 
controlled descent onto the asteroid, sending dozens of 
high-resolution pictures as the spacecraft closes in on Eros.  
 
The NEAR mission will be the first close-up study of an asteroid.  
APL, the first non-NASA center to conduct a NASA planetary mission, 
is managing the mission for NASA's Office of Space Science, 
Washington, DC.   
 
Information on the NEAR mission, including a list of areas most 
likely to see NEAR's sunglint and how to find NEAR as it swings by 
Earth, is available on the Internet at:
http://sd-www.jhuapl.edu/NEAR/

=========================================================================
(6) NEAR S/C EPHEMERIDES AVAILABLE ON WORLD WIBE WEB

From: Don Yeomans 

NEAR S/C ephemerides available

Jon Giorgini and Alan Chamberlin have recently included the Near 
spacecraft ephemeris files within our Horizons on-line ephemeris  
service and also on our interactive web page.

For those interested in observing the NEAR spacecraft on its Jan 
22-23 Earth flyby, the trajectory can be accessed via JPL's on-line 
ephemeris system, Horizons.

This will allow you to compute customized spacecraft ephemerides for
your particular site (600 sites on file, or input your own 
coordinates). Tabular quantities include azimuth, elevation, RA, DEC, 
angular rates, distances, velocities, rise/set, state vectors, + 
more, at user selected time steps.

To access, telnet to port 6775 on machine ssd.jpl.nasa.gov:
telnet ssd.jpl.nasa.gov 6775

No password or ID required. At the prompt, type "NEAR", and follow
subsequent prompts. Type ? or ?! at any prompt for help. Documentation
at ftp://ssd.jpl.nasa.gov/pub/ssd/Horizons_doc.ps

The system can be accessed by WWW. See 
http://ssd.jpl.nasa.gov/cgi-bin/eph

Select the spacecraft and set appropriate times and observing sites.

Trajectory data developed and provided by the NEAR Navigation Team
at JPL:  Bobby Williams, Jim Miller, Cliff Helfrich
Follow-Ups: