PLEASE NOTE:


*

CAMBRIDGE-CONFERENCE DEBATE, 30 March 1998
------------------------------------------

(1) WHAT SHOULD WE FEAR FROM PLANETARY DEFENSE SYSTEMS?
    Bob Kobres <bkobres@uga.edu>

(2) AANEAS VALEDICTORY REPORT
    Duncan Steel <dis@a011.aone.net.au>

(3) HYPOTHESISED PHYSICS OF THE "JOSHUA" EVENT
    Ed Grondine" <epgrondine@hotmail.com>

==========================
(1) WHAT SHOULD WE FEAR FROM PLANETARY DEFENSE SYSTEMS?

From: Bob Kobres <bkobres@uga.edu>

I’ve tried to understand the logic of people who, like Alan W. Harris
(NEO DEFLECTION SYSTEM FAR TOO DANGEROUS TO DEVELOP, C-C DEBATE, 26
March 1998), believe that effecting an Earth defense system would be
more dangerous than taking our chances. I too opposed SDI and my EDI
(Earth Defense Initiative) proposal was basically an argument for the
redirection of resources away from war preparation to environmental
protection. The most important part of the ‘Star Wars’ inventory that I
was hopeful of being put to better use was the people employed by that
program. Harris’ distrust of “the folks who brought you Star Wars”
seems excessive. Are all these people truly demonic and just waiting
for a chance to do in the world?  And how is PHO deflection equipment
designed to operate exclusively in space somehow more dangerous than
submarines armed with thermonuclear devices lurking in international
waters?

I’m open-minded Al. What should we fear from a project to protect Earth
that involves the use of thermonuclear devices, and why?

bobk

Pertinent pages:
http://abob.libs.uga.edu/bobk/nucreaim.html
http://abob.libs.uga.edu/bobk/meteor.html
http://abob.libs.uga.edu/bobk/petition.html
http://www.au.af.mil/au/2025/volume3/chap16/v3c16-1.htm

Bob Kobres
==================

(2) AANEAS VALEDICTORY REPORT

From: Duncan Steel <dis@a011.aone.net.au>

Dear Benny,

I note that you mentioned the near-Earth asteroid search and tracking
program which we had in Australia from 1990-96.  For details of what we
did and what we achieved, see a preprint of our paper entitled 'AANEAS:
A Valedictory Report' at:

http://www1.tpgi.com.au/users/tps-seti/spacegd4.html
(other links there may also be of interest to readers).

That program I named AANEAS (Anglo-Australian Near-Earth Asteroid Survey),
because we made use of AAO facilities; for clarification, note that all
funding for the project came from the Australian government, not that of the
UK, and we were charged by the AAO for the use of various facilities.  It
should not, therefore, be represented as being an AAO project.
Basically it was my project in that I raised all the funding and
directed the effort, with the major contribution to the actual
observational work coming from Rob McNaught, aided by Gordon Garradd,
David Asher and myself.

Duncan Steel

=====================
(3) HYPOTHESISED PHYSICS OF THE "JOSHUA" EVENT

From: Ed Grondine" <epgrondine@hotmail.com>

Dear Jonathan -

As you point out, most breakups of large unitary meteoroids occur
at high altitudes, usually 10 or more miles up. But this varies
depending upon the meteoroid's composition and speed: Tunguska exploded
at about 5 miles altitude, Sikhote Alin at 3.6 miles.

What is a possible scenario for the "Joshua" event? A large 
meteoroid broke up at an even higher altitude than Tunguska. Its entry
may not have been seen from the ground due to a thick cloud cover, which
also absorbed the radiant energy from the breakup. (Think of Tunguska,
but much smaller, occuring even higher up: The clouds get blasted
instead of the ground.)

Since it is a large meteoroid, while its surface has been red hot,
deep in its interior it is still as cold as space. While most of the
meteoroid is converted to a very fine dust which floats up into the
stratosphere, causing the lighting effect seen later, some of it at the
very center remains intact, falling to the ground as stones. Other
pieces left from deep in the core, and very cold, are smaller than
these, but larger than the fine of the dust, and these pieces drift down
to the cloud cover. When they come in contact with the heated cloud
cover, hail results.

Of course, this is only one possible description of an event whose
very occurence has not been proved yet, and for which direct
geo-physical evidence is completely lacking at this time. While I am
hoping that the meteorite collecting community may find material 
evidence of the event, it may be necessary to conduct a field
expedition. I notice from your note that you have participated in the
British Antarctic Survey; I have attached an appendix to this note
comparing the two.
                                            Good Hunting! -
                                              E.P. Grondine 
 
APPENDIX I:

COMPARISON OF ANTARTIC SURVEY WITH BETH HORON SURVEY

PURPOSE:
Antarctica  - To recover individual specimens,
              miles from their point of impact.
Beth Horon - To recover debris field by mapping specimens
             at their point of impact.

TRANSPORT:
Antarctica  - C-5A canvas seats to packed ice field.
Beth Horon - El-Al to Tel Aviv; 
             To reduce expedition costs,
             economy is flown instead of first class.

LODGING:
Antarctica  - Prefrabricated hut on ice field.
Beth Horon - Tourist hotel already built in area.

ON-SITE TRANSPORT:
Antarctica  - Tracked ice crawler, helicopter.
Beth Horon - Car.

CLOTHING:
Antarctica  - Muliple layers of insulated clothing
              to protect against sub-zero cold.
Beth Horon - Shorts and t-shirts
             to protect against midday heat.

FOOD:
Antarctica  - Freeze dried food re-hydrated,
              then heavily seasoned to improve palatability.
Beth Horon -  Expedition members food intake insured by food variety:
              Different restaurant visited every night.

PSYCHOLOGICAL HEALTH:
Antarctica  - Expedition members kept in short wave radio contact
              with distant family members, colleagues, and supervisors.

Beth Horon - Expedition members kept out of contact with family
             and normal workplace, in order to ensure their focus on              
     mission.
 
DAILY SCHEDULE:
Antarctica  - Expedition members take breaks to ensure that
              nose, ears, and other extremities do not suffer          
              frostbite and fall off.
Beth Horon - Expedition members take noon break at hotel swimming pool
             to ensure that they do not succumb to heat.
Antarctica  - Round the clock daylight ensures that
              collecting is possible at all hours.
Beth Horon - Nightfall ends collecting;
             Expedition members eat dinner;
             Planning session for next day's hunt
             held at bar so that expedition members can re-hydrate.



*

CAMBRIDGE-CONFERENCE DIGEST, 30 March 1998
------------------------------------------

(1) A LETTER TO TIME MAGAZINE FROM THE SPIRITUS RECTOR OF SPACEGUARD
    Sir Arthur C Clarke

(2) HOW THE ASTEROID 1997 XF11 STORY HIT
    Brian Marsden <brian%cfaps1.span@vms.noao.edu>

(3) IMPACT HAZARD AND THE XF11 AFFAIR
    Clark Chapman <cchapman@boulder.swri.edu>

(4) GERVASE'S 1178 'LUNAR IMPACT' HAS PROBLEMS
    Brad Schaefer <schaefer@grb2.physics.yale.edu>

==========================

(1) A LETTER TO TIME MAGAZINE FROM THE SPIRITUS RECTOR OF SPACEGUARD

From: Sir Arthur C Clarke

To Leon Jaroff
   TIME
   (Via Russ Galen)

Dear Leon,

TIME must have a short memory!  I am astonished, and rather annoyed,
that your write-up of 1997 XF11 didn't mention the fact that in 1992
you commissioned The Hammer of God which described exactly such an
event and what we should do about it. The short story was published in
your special issue of 28th September and the novel came out from Bantam
the next year.

Also it was optioned by Dreamworks, and presumably parts of it have
been incorporated in Deep Impact - in fact the scene TIME shows might
very well have been taken from Hammer. When Worlds Collide is a totally
different story, because it concerns another solar system, and an event
which would take place over hundreds of thousands of years!

You might also mention that I introduced the term "Spaceguard" in
Rendezvous with Rama. This name is now being used by NASA and others.
Rama has just been optioned by Morgan Freeman (who appears in Deep
Impact.)

Incidentally, have you heard the suggestion that the Chicago fire was
actually due to a shower of meteorites?  Apparently, there were
conflagrations all around Chicago that could not have spread from the
City in such a short time - and there were also reports of phenomena in
the sky. This might be well worth investigating.

               All best,

               Sir Arthur Clarke

P.S.  Department of Modest Coughs
On another topical subject - I discussed lunar ice mining - with an
illustration, in The Explorations of the Moon (1954) and there is a
romantic description of tractor trains carrying ice from the south
polar mines in 2061:Odyssey Three.

======================
(2) HOW THE ASTEROID 1997 XF11 STORY HIT

From: Brian Marsden <brian%cfaps1.span@vms.noao.edu>

** This is an extended version of an article that appears on pages E1 and E2
   in the FOCUS section of the "Boston Sunday Globe" on 1998 March 29

HOW THE ASTEROID STORY HIT: AN ASTRONOMER REVEALS HOW A DISCOVERY SPUN
OUT OF CONTROL

Brian G. Marsden

There was a dramatic worldwide response to my announcement earlier this
month that an asteroid known as 1997 XF11 would pass perhaps
uncomfortably close to the earth on a date 30 years hence, with an
exceedingly remote chance that it could strike, subject to further
study of its path.

Less than 30 hours later, it was still true that the asteroid would
pass close to us, though not excessively so, on that date. But the
worry was off, and initial concerns had been replaced by jokes about
astronomers making mistakes, as in, "No wonder math education in this
country has its problems".

Along with such comments came accusations of "Chicken Little" behavior
by "irresponsible" Harvard astronomers neglecting to check their
"cockamamie calculations" with colleagues first (columnist William
Safire), and complaints that some NASA scientists were muscling in on a
matter that really didn't concern them, a case of "professional
discourtesy" (Malcolm Browne, in The New York Times).

Of course, as many other scientists and journalists pointed out, the
now greater distance from the earth of this asteroid's projected path
did not alter the fact that there will come a next time, when a sizable
comet or asteroid strikes with disastrous consequences, but it provided
some reassurance that, for the moment at least, we can sleep easily.

So what went wrong with asteroid XF11?  In my view from the eye of the
storm, the problem was an overeager use of e-mail and public relations
by a supervisory scientist at NASA's Jet Propulsion Laboratory (JPL). I
also believe that for us not to make the announcement as we did would
have led to  condemnation that science was being stripped of its
essential openness.

Asteroid passes are more frequent and closer than most people think. 
Just 30 years ago, on June 14, 1968, the asteroid Icarus, roughly the
same size as 1997 XF11, passed 4 million miles from the earth. That
seems like a tremendously safe distance (and it is), but much of the
public and the press did not think so at the time. A younger and
slimmer yours truly was interviewed about the Icarus encounter a day or
two beforehand by a younger and slimmer Chet Curtis of Boston's Channel
5, a cult gathered on a peak in Colorado to escape from the anticipated
slide of California into the Pacific Ocean, and I spent several minutes
on the phone calming a woman whose mother was terrified about the
impending end of the world. 

It was all unnecessary. Icarus had been expertly tracked by astronomers
from its discovery in 1949 frequently through 1967, and the distance of
4 million miles was precise.  But because it was only the first time an
asteroid had been predicted to come that close, many people went wild.

Icarus is the fifth entry on the list of "potentially hazardous
asteroids", or PHAs, that have the possibility, over the next several
centuries, of coming within 5 million miles of the earth and that are
more than perhaps a tenth of a mile across.  Icarus next comes to a
distance of 5 million miles in 2015.  And it will continue to induce
scares, as it did in fact just a few weeks ago, when there appeared in
many countries a claim in the press that it will definitely hit the
earth just eight years from now! This was complete nonsense, for the
miss distance in 2006 will be 30 million miles: even the planet Venus,
almost as large as the earth, comes closer than that, and it does so
every 19 months.

More of a worry in 1968 was the fact that there were perhaps half a
dozenother known PHAs (though we didn't call them that then) that had
been lost since within weeks of their discoveries.  The first PHA,
known as Apollo, had been discovered way back in 1932.  It was a bit of
long shot, but in 1973 I worked with two colleagues using the 61-inch
telescope in Harvard,Mass., in a successful hunt for Apollo.  As a
result of this rescue, we now know where Apollo will be for centuries
to come--and we know that the earth is safe from it. 

On the other hand, Hermes, observed for only four days in 1937 (with
the first known photograph also having been obtained at the Harvard
station), is still very much lost.  It could be anywhere around its
orbit. Some October day (or, perhaps, an April day) in the years to
come, Hermes could indeed be a threat to us. With luck, the programs
that search for PHAs and other asteroids that come moderately near the
earth will accidentally record Hermes well before that day.  With
appropriate measurements, we shall be able recognize that it really is
Hermes.  The rediscovery of Hermes is one of those prizes that quite a
few astronomers wish for at the back of their minds. Furthermore, for
each Hermes, there are 20 or more unknown possible threats of
comparable size that we don't already know.

The first program set up specifically to search for "NEOs" (i.e., "Near
Earth Objects", a more general term than PHAs) was initiated in 1973 by
Caltech's Eleanor Helin in collaboration with the late Gene Shoemaker and
using wide-field telescopes at the Palomar Observatory in California. 
The Helin and the Shoemaker programs went their separate ways in the
early 1980s, when Gene began to collaborate with his wife, Carolyn. 
The other early entrant into the NEO search business was Tom Gehrels,
who was photographing asteroids already in the 1950s and who in the
1980s set up the University of Arizona's "Spacewatch" project, the
first program to make the asteroid detections efficiently by electronic
means, rather than from scanning conventional photographs by eye.  In
1995, Helin's program also "went electronic", and her team in
California is now engaged in the analysis of images relayed to them six
nights a month from a telescope operated by the Air Force in Hawaii. 

The programs of the veteran researchers Gehrels and Helin have recently
been joined by an excellent third search program, which also uses an
Air Force telescope (in New Mexico) and is operated by a group at MIT's
Lincoln Laboratory here in Lexington. My offices at the
Harvard-Smithsonian Center for Astrophysics in Cambridge have worked,
and continue to work, closely with all these search programs, as well
as with other astronomers (professional and amateur) around the world
who make follow-up observations of interesting objects that are found. 
We correlate and otherwise organize the data from the various groups
and observers, compute orbits as appropriate and attend to the
communication of the results under the auspices of the International
Astronomical Union (IAU), the international association of professional
astronomers.

It was an assistant in the Shoemaker program who, in 1989, discovered
the asteroid Asclepius, which at a distance of only 430 thousand miles
came closer than any known asteroid since the lost Hermes.  There was
the particular worry that Asclepius had actually made its pass a week
before it was discovered, and that was because it came at us from the
direction of the sun. 

Beginning in 1991, there were several occasions when Spacewatch
discovered tiny asteroids, only tens of feet across, at distances of
100 thousand miles and even less.  Objects this small really are of
little concern, because even if they hit, they are likely to burn up
completely and harmlessly in the earth's atmosphere. 

Then, in 1996, came the PHA with the closest known pass, 280 thousand 
miles, for an object perhaps one to two tenths of a mile across. It was
discovered photographically by two enterprising students in Arizona,
Tim Spahr and Carl Hergenrother, only a few days before its closest
approach.

The subject of the latest concern, 1997 XF11, was discovered in
December by Jim Scotti of Spacewatch and is the largest of the 11 PHAs
added last year.

(A complete list of the 112 known PHAs appears in our Web site at
http://cfa-www.harvard.edu/iau/lists/Dangerous.html. The site also has
a list of all the predicted approaches of asteroids and comets within
about 19 million miles of the earth during the next third of a century:
see http://cfa-www.harvard.edu/iau/lists/CloseApp.html.)

On March 11, when my colleague Gareth Williams and I were making our
regular monthly update of our Web files on March 11, we were startled
to find 1997 XF11 singled out for a passage less than 30,000 miles from
the center of the earth on Oct. 26, 2028.  In more than 40 years of
computing orbits, I had never seen anything like that before.  Of
course, we realized that the actual distance was uncertain and that the
object could easily pass at or somewhat beyond the distance of the
moon.

Nevertheless, to have the earth right at the center of the uncertainty
range was startling.  What really surprised us, however, was that
nobody else --the folks at JPL, for example, or even a knowledgeable
amateur astronomer with a PC--seemed to have done this same calculation
yet, since all the information necessary had been available on the Web
for five days.

In fact, nobody seemed to have taken much interest in the object at
all, even though it was obvious already in December that XF11 was an
asteroid that could come particularly close to the earth and that it
was in the largest 20 percent of all PHAs.  This reinforces the
impression that we must hunt for PHAs because if we don't do so, we
shall someday go the way of the dinosaurs. Yet some colleagues appear
to assume that the PHAs we have already detected cannot possibly hurt
us, and we don't need to study them any more.

With our attention drawn to XF11, the obvious next course to us was to
encourage further observations, either in the future--with the object
now getting rather faint and due to move into daylight in a couple of
months--or in the past, with images perhaps to be found in photographic
archives. 

I therefore put out an "IAU Circular" stating the facts and telling
observers where to look for XF11 between now and early July.

As we sometimes do with a particularly interesting development, we also
put a popular version of it into our Web page.  The popular rendition
mentioned the possibility of finding images of XF11 on photographs
taken in 1990 and earlier. By "clicking" on a particular year, one
could see where in the sky the object was.  If earlier images were
found, they could provide more precise determination of the asteroid's
course than we had available.

Eleanor Helin (who, as it happens, is also now located at JPL) and
assistant Ken Lawrence checked the Web site, realized they had suitable
Palomar telescope films in 1990, inspected them, quickly found the
images of XF11 from March 22 and 23 of that year, measured them and
reported the measurements to us. Great. 

Williams worked the 1990 data into the orbit solution, revised the 2028
miss distance to 600,000 miles, and I prepared another IAU Circular
with the new results. (This will still be the record predicted approach
for an asteroid or comet during upcoming decades.  Although we know of
an asteroid that will come just a little closer in 2086, it seems to be
smaller than 1997 XF11.)

So where did things go awry? The media, of course, make an easy
scapegoat. But responsible science writers, such as Browne and David
Chandler of the Globe, wrote quite commendable articles. These writers
receive the IAU Circulars on a regular basis anyway. What's the
alternative way of getting news out? Should we prohibit anyone with
press credentials from even looking at our Circulars? Some of my
colleagues are looking into ways of preventing information on wayward
PHAs from getting to the press and the public. To me, that smacks of
censorship.

No, I think the problem lay with some of those very colleagues, eager
to make pronouncements. And the reason this is a problem now is the
easy availability of e-mail. E-mail is a wonderful tool--often better
than the telephone--for getting quick answers to urgent questions.  But
many e-mail devotees use it not just to send a message to someone but
to copy that message simultaneously to a couple of dozen other people.

This prompts responses and remarks between other pairs of participants,
with the messages again copied to all the members of the gang, plus,
perhaps, a few more friends. Those friends also have their regular
e-mail correspondents, of course, so both information and
misinformation can proliferate rapidly, like a pyramid scheme.

Paul Chodas is a fine scientist at JPL, and on receiving the message
about XF11, he performed some experiments on the uncertainty of the
miss distance to see whether there was possibility the object might hit
the earth in 2028. Chodas's computations were not, in fact,
significantly different from mine. The difference was that an official
there e-mailed his results to all and sundry, thereby also bringing
them to the attention of the press.

Chodas and I agreed, as did two other scientists making similar
calculations, that it would be very difficult to bring XF11 within
15,000 to 20,000 miles of the earth's center in 2028. But that is
closer than the geosynchronous artificial satellites. Furthermore, the
other scientists working on the problem agreed with me that it was
rather rash to say that there was absolutely no chance of a strike, for
it was impossible to claim there could not be other unconsidered
effects (such as an abnormal distribution of errors, the ignored
gravitational effect of a close approach to another asteroid, the
possible reaction of the object to the explosive vaporization of ice on
the surface).

A rip-roaring e-mail barrage on such small points quickly developed. As
far as I was concerned, the argument was irrelevant. Matters would be
solved once and for all if someone would do what I suggested and look
for images of XF11 on past photographs. In any case, as Chandler later
described in the Globe, there was an error in Chodas's
computations--and Chodas was man enough to admit it.

And, of course, as soon as the 1990 observations became available, it
was obvious that my group and the JPL group would obtain the same
result with the 600,000-mile miss: revealing absolutely no danger. 
Again, what I thought inappropriate was the release of the new data by
an official to colleagues and the press, with no mention that we and
JPL were in agreement, given that the Circular with Williams's
calculation (and a revision to our Web page) had been issued 90 minutes
earlier.  Contrary to reports, there was no "mistake" in either set of
computations made by our group in Cambridge. What there was were new
data, properly reported.

A few of my colleagues have questioned whether it was appropriate to
issue an IAU Circular with a call for observations of XF11, when I
could instead perhaps have contacted Helin and others directly with
regard to checking past photographs. My response to this is that I did
not know in advance whether she or others (which others?) would have
appropriate old films. If there were no old films at all, it was
obviously important to make future observations, and time for these was
running short. 

If there were no sense of urgency, there would be no incentive to
search archives immediately, and they might not have been searched
until future observations became impossible.  In any case, it is
precisely for the timely acquisition of follow-up observations like
this that the IAU Circulars exist. If one asks observers individually,
that is much more inefficient, and there are bound to be some who do
not get asked--and who may as result feel a bit miffed.  As it
happened, we had a response from an astronomer in Germany concerning a
possible image--not confirmed, it seems--of XF11 from way back in 1957.
Would I have thought to solicit that astronomer directly? 

The only other known positive past detections of XF11 to date are from
the Shoemaker team, also made in 1990.  The fact that there were such
detections (but not the measurements themselves) was relayed to our
offices some six hours after Helin informed us that her team had
detections, and in the mean time she had provided the necessary
measurements. Science may strive to be objective, but scientists are as
competitive as anybody else. We made the information about where to
look in 1990 available in the Web. That put all the film searchers on
an equal footing. Nobody had an unfair advantage over anybody else.

At a meeting organized by NASA in Houston on March 17 some
consideration was given to changing the procedures for announcing
possible "end of the world" scenarios in the future. There was talk of
establishing a special committee to "verify the orbit computations", as
well as to alert those who might be able to make further observations
and search for images in past archives. This is one of those proposals
that may sound good, but as I have just indicated, there would clearly
be problems as regards crediting priority for observations and archival
searches--indeed, also, as regards crediting priority for ideas. 
"Science by consensus" is really not a palatable way to go, and
decisions by committees are the food for cover-ups. In any case, the
XF11 orbit computations announced were the correct conclusion from the
data available at the time, and there was independent verification of
this by both Williams and myself.  Furthermore, it is surely naive to
believe one can stop everyone everywhere from talking to his or her
favorite reporter.

Certainly, I appreciate that there was a problem that the leaderships
of both the IAU and NASA were embarrassed by this episode, in the sense
that they had not in fact seen the initial Circular before they were
overwhelmed by the press. I have indeed apologized to them for catching
them unawares and hope that a way can be found to warn them and perhaps
others of this kind of thing in the future.

I don't expect to be around in 2028 myself, but I can say that, weather
and intervening disasters permitting, astronomically inclined residents
of Massachusetts ought to be able to follow the asteroid on the morning
and evening of the appointed day. A tiny starlike object will move from
east to west (and in near full moonlight, if the night stays clear).

Few will remember it as 1997 XF11 then, because it will have received a
real name, perhaps at the time of its 6-million-mile pass in 2002. But
some will remember the brief fiasco in 1998 and perhaps reflect that
this represented a genuine turning point. For one thing, perhaps 1998
would signal the beginning of a genuine breakthrough in significantly
improving the quality of U.S. education in math and science all the way
through grade 12. If so, the passage of XF11 in 2028 would be treated
with the knowledge and the respect it deserves, with Heavensgate-type
behavior and its associated ignorance a thing of the past. Furthermore,
recalling the conclusions of the Spaceguard Survey Report of 1992 that
a concerted survey both to discover and to track more than 90 percent
of the most dangerous PHAs would take two to three decades, our
successors watching the skies of 2028 might appreciate that XF11
provided the inspiration that led to funds to patrol the skies for
PHAs much more thoroughly than before.

___
Brian G. Marsden is associate director for planetary sciences at the
Harvard-Smithsonian Center for Astrophysics in Cambridge and director
of both the Central Bureau for Astronomical Telegrams and the Minor
Planet Center of the International Astronomical Union

================================
(3) IMPACT HAZARD AND THE XF11 AFFAIR

From: Clark Chapman <cchapman@boulder.swri.edu>

You may be interested in a revised case study I have prepared
concerning the impact hazard, including its history up through, and
including, an evaluation of the recent 1997 XF11 affair. It is an
intermediate revision of a document written as part of a project by the
Geological Society of America and the National Center for Atmospheric
Research (sponsored by the NSF) to evaluate the role of "predictive
science" in the public policy arena.  A link at the top of my URL,
which follows, will tell you more about that larger effort, which
includes earthquake prediction, the Weather Service, global warming,
etc.

www.boulder.swri.edu/clark/ncar.html

Clark Chapman

====================
(4) GERVASE'S 1178 'LUNAR IMPACT' HAS PROBLEMS

From: Brad Schaefer schaefer@grb2.physics.yale.edu

Here is a contribution for the Cambridge Conference, with the topic of
Gervase's 1178 event inspired by the recent note:

GERVASE'S 1178 'LUNAR IMPACT' HAS PROBLEMS

Carl Sagan's Cosmos dramatically portrayed the report of Gervase of
Canterbury, that on the evening of 18 June 1178 a group of monks near
Canterbury saw what J. B. Hartung (1976 Meteoritics, 11, 187)
interpretted as a giant meteor hitting the Moon. Gervase says "... five
or more men who were sitting there facing the Moon. Now there was a
bright new Moon, and as usual in that phase its horns were tilted
towards the east; and suddenly the upper horn split in two. From the
midpoint of this division a flaming torch sprang up, spewing out, over a
considerable distance, fire, hot coals, and sparks..." Hartung's
identification of the 'impact' site with the young crater Giordano
Bruno is highly evocative.

In 1984, Ken Brecher (BAAS, 16, 476) made the nice connection of this
Canterbury Event with the swarm of meteors, comets and asteroids
associated with the orbit of Encke's Comet. This association is made
solely on the basis of the date. Christened the "Canterbury Swarm", the
dangers of impacts from swarms of debris is well highlighted.

But Gervase's report has a two serious problems which strike at the
heart of Hartung's hypothesis. The biggest problem is that the crescent
Moon would not have been visible on the stated date (Meeus 1990, JBAA,
100, 59). [With all my theoretical and observational experience on
crescent visibility questions, I chide myself for not having done Meeus
calculation first, but after the fact I do confirm Meeus' conclusion.] 
So the direct  statement of Gervase cannot be correct, nor is it
possible that a backside impact could have lit up the Moon enough to
allow visibility.

If Gervase merely reported the wrong date, then perhaps it might
be possible to save the claim. Indeed, Gervase misreports 15 dates that
I have identified, including for three solar eclipses. However, there
is no independent reason to suggest a date error. Once anyone
starts getting into the game of 'let-us-arbitrarily-change-the-
text-so-as-to-fit-my-preconceived-hopes', then the proof of anything is
possible. In particular, the arbitrary assumption of a date invalidates
the connection with the Canterbury Swarm since the date is the only
connection.

Another serious problem is familiar to readers of ancient and medieval
chronicles, where many fabulous prodigies are reported second-hand. 
Gervase has his share of them, so the authority and believability leave
too much to modern assumptions.

So our community should not make too big a deal about the Canterbury
Event, or skeptics can use this to discredit by connection all the
other very strong evidence of large impacts.

Cheers,
Brad Schaefer
Yale, Physics, JWG 463
New Haven CT 06520-8121 USA

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