Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_3/V15NO357.TXT

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Date: Fri, 30 Oct 92 05:00:06
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #357
To: Space Digest Readers
Precedence: bulk


Space Digest                Fri, 30 Oct 92       Volume 15 : Issue 357

Today's Topics:
          "Earth gains a retinue of mini-asteroids" (2 msgs)
                        A career in Aerospace?
             Apollo - Southern Style with a side of grits
                           Comet Collision
                       Mini-asteroids part two.
                          orbit code needed
                              Post WARC
                Putting volatiles on the moon (2 msgs)
                    QUESTIONS: Apollo, Earth, Moon
               Re:Swift-Tuttle Comet a threat to earth?
                   Scenario of comet hitting Earth
                         Solar Sails (3 msgs)
                Swift-Tuttle Comet a threat to earth?
                     UFO EVIDENCE VS. Carl Sagan
         What does the "P/" mean in P/Swift-Tuttle? (3 msgs)

    Welcome to the Space Digest!!  Please send your messages to
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----------------------------------------------------------------------

Date: 29 Oct 92 17:07:29 GMT
From: Paul Dietz <[e-mail]>
Subject: "Earth Gains a Retinue of Mini-Asteroids"
Newsgroups: sci.astro,sci.space

Science (10/16/92, page 403), reports that Gehrels and colleagues in
the Spacewatch program have detected 8 very near earth asteroids over
the last two years with sizes from 5 to 100 meters.  This implies that
at any time, there are as many as 50 mini-asteroids passing between
the Earth and Moon every day.  This figure is some 100 times larger
than had been inferred from observations of the number of larger
bodies.

Since the Tunguska event is thought to have been due to a 40 meter
body, and such events were calculated to occur once every 2 to 3
centuries, something is screwy here.

The orbits of the bodies are unexpectedly similar to Earth's.
Two have orbits more like earth's than any known body; one was that
asteroid that was mistaken for a spent rocket body.

These couldn't be Frank's minicomets, could they?  His putative
objects are supposedly in prograde, earth-like orbits, to reduce the
impact velocity enough to avoid observational constraints.

    Paul F. Dietz
    [e-mail]

------------------------------

Date: Thu, 29 Oct 92 13:11:40 -0600
From: [e-mail] (Phil G. Fraering)
Subject: "Earth gains a retinue of mini-asteroids"

>The orbits of the bodies are unexpectedly similar to Earth's.
>Two have orbits more like earth's than any known body; one was that
>asteroid that was mistaken for a spent rocket body.

>These couldn't be Frank's minicomets, could they?  His putative
>objects are supposedly in prograde, earth-like orbits, to reduce the
>impact velocity enough to avoid observational constraints.

I think Frank's minicomets, although I don't have the ref.
with me, were supposed to be a little faster than this, but
still prograde.

And a lot dimmer.

I'd bet Frank will claim that these bodies represent the "larger"
members of his mini-comet population, but I don't know.

I do know that Dr. Louis Frank has an e-mail address. Proof is
left as an exercise for your local Gopher server. And I'm sure
he's better qualified to tell you his opinions than I am.

I'm not sure I agree with him, but his book was pretty good...

 --
Phil Fraering [e-mail] where the x is a number from 1-5.
Phone: [phone] SnailMail: 2408 Blue Haven Dr., New Iberia, La. 70560
---------------------
Disclaimer: Some reasonably forseeable events may exceed this
message's capability to protect from severe injury, death, widespread
disaster, astronomically significant volumes of space approaching a
state of markedly increaced entropy, or taxes.

    The world will end tomorrow.
    NASA scientists note that this was the way the system was
    designed to operate.

    - From the Nov. Focus in Sky and Telescope, on a hypothetical
      NASA press release on something hitting the Earth...

------------------------------

Date: Thu, 29 Oct 1992 10:59:33 -0500
From: [e-mail]  (John Judge)
Subject: A career in Aerospace?

I am a college freshman considering a career in aerospace.  What are the
chances that the job market will improve by the time I graduate?
                                        John Judge

------------------------------

Date: 29 Oct 92 18:55:03 GMT
From: Spiros Triantafyllopoulos <[e-mail]>
Subject: Apollo - Southern Style with a side of grits
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>In article <[e-mail]> [e-mail] writes:
>>Bill Higgins proclaims:
>>>>>It worked, too.  Southerners put us on the Moon...
>
>>>> At Lewis there is a persistant rumor that they could not have
>>>>done it  without some help from North of the Mason-Dixon line...
>
>>   And a few California drawls too, dude....

How about a few Milwakee-ans? Delco (AC Electronics at the time) built
computer hardware for the Apollo program. The automotive electronics
program started with many of the Apollo hardware folks from Milwakee.
I've seen Apollo project reunions in our internal literature.

The moon rover was built by GM, but I believe it was done in dude
country (Southern California).

Spiros
--
Spiros Triantafyllopoulos                    [e-mail]
Software Technology, Delco Electronics       [e-mail]
GM Hughes Electronics, Kokomo, IN 46904      [A Different Kind of Disclaimer]

------------------------------

Date: 29 Oct 92 15:43:35 GMT
From: [e-mail]
Subject: Comet Collision
Newsgroups: sci.space

In article <[e-mail]>,
[e-mail] (Bruce W. Morlan) writes:
> [e-mail] (Richard S. Brice) writes:
>
>>Would anyone care to comment on how probability plays a role in the
>>future interactions of earth and comet P/S-T and how much of the
>>script is already written into the clock?
>
> Sure.  The script is nearly totally written.  The Heisenberg uncertainty
> associated with the objects in question (Earth, comet, Sun, other
> planets, etc.) is practically 0 over the time frame in question.  On the
> other hand, the _uncertainty_ in the measurements leave much room for
> surprises.  I cannot comment on the measurement errors.

Just what does Heisenberg uncertainty have to do with this?  We're not
talking about a system small enough or fast enough to need any of the
tools of Quantum Mechanics.

-Bill Gawne,  Space Telescope Science Institute

------------------------------

Date: Thu, 29 Oct 92 13:33:32 -0600
From: [e-mail] (Phil G. Fraering)
Subject: Mini-asteroids part two.

>Since the Tunguska event is thought to have been due to a 40 meter
>body, and such events were calculated to occur once every 2 to 3
>centuries, something is screwy here.

I've done some more thinking about this. Let's fudge the properties
of these objects so that they don't conflict with what we've already
seen:

Specifically, let's make them low density, so they don't hold together
well, or last long enough in the atmosphere to cause a big show.
Snow would be an ideal candidate.

Of course, if they were bare ice, they'd be bright, so let's give
them a coating of that gooey stuff that was on the rings of
Uranus and Neptune, to make them more reasonably dark.

Now they also absorb radar signals.

But this sounds too much like _that_ guy's theory, so it can't
be right...

>The orbits of the bodies are unexpectedly similar to Earth's.
>Two have orbits more like earth's than any known body; one was that
>asteroid that was mistaken for a spent rocket body.

>These couldn't be Frank's minicomets, could they?  His putative
>objects are supposedly in prograde, earth-like orbits, to reduce the
>impact velocity enough to avoid observational constraints.

Now that I think about it, Frank has (again going from memory)
specified the orbital parameters of these hypothetical bodies pretty
closely...

These might be the _slower_ members of the population...

>    Paul F. Dietz
>    [e-mail]

Disclaimer: I don't know; I'm just guessing.

Anyone here read _The Big Splash_?

--
Phil Fraering [e-mail] where the x is a number from 1-5.
Phone: [phone] SnailMail: 2408 Blue Haven Dr., New Iberia, La. 70560
---------------------
Disclaimer: Some reasonably forseeable events may exceed this
message's capability to protect from severe injury, death, widespread
disaster, astronomically significant volumes of space approaching a
state of markedly increaced entropy, or taxes.

    The world will end tomorrow.
    NASA scientists note that this was the way the system was
    designed to operate.

    - From the Nov. Focus in Sky and Telescope, on a hypothetical
      NASA press release on something hitting the Earth...

------------------------------

Date: 29 Oct 92 18:18:46 GMT
From: Douglas Strickland <[e-mail]>
Subject: orbit code needed
Newsgroups: sci.space

Hello:

   I am in need of an orbit code for satellite altitude approximately at
800 km (period is about 100 minutes, I think). It has to be fairly
accurate so I can not use codes written for amateurs.

   Does anyone know about the availability of such software, public or
commercial, perhaps in FORTRAN?

   Thanks in advance.

Mike Shen
[e-mail]

------------------------------

Date: 28 Oct 92 10:48 PST
From: Public Service Telecommunications Consortium <[e-mail]>
Subject: Post WARC
Newsgroups: sci.space

On the assumption there are people on the conference concerned
with telecommunications and space, I would like to solicit some
views, especially from European readers.  The World Administrative
Radio Conference (WARC) provided a variety of allocations for new
services.  I am especially interested in LEOs, and the set
asides for their operation.  The U.S. delegation to WARC came
home claiming victory; it had obtained what was wanted for
Motorola's IRIDIUM and others like it.  The European post-
WARC view was that the U.S. should not be so sure of itself;
one delegate was quoted as saying, "the devil is in the details."
The "details," in this case, were the many footnotes and
reservations not seen by all when the Final Acts were signed
in a frenzy of late night activity.  I know it is difficult to
make predictions, especially about the future, but I'd be
interested in informed views of how things are going to
shape up, especially in light of European displeasure with
the results the U.S. thinks it obtained.  If you'd care
to answer via e-mail, many thanks and I'm Bert Cowlan,
Public Service Telecommunications Corporation, a nonprofit
thinktank.  Address <pstc>.

------------------------------

Date: 29 Oct 92 02:28:51 GMT
From: "John A. Weeks III" <[e-mail]>
Subject: Putting volatiles on the moon
Newsgroups: sci.space

In <[e-mail]> [e-mail] writes:
> As a method of steering the comets, a few large nukes could give a comet
> enough of a push to do the job. Also a good usefull way of turning swords
> into plowshares! I find that it is a wonder that man is so hesitant to use
> his most powerful tool for anything except as a weapon.

Eeek! I was looking for a smiley at the end of your post, but I didn't
find one.  While I don't know about using nukes to nudge comets, I have
recently heard a few stories about the Soviet Union using nuclear bombs
for peaceful purposes.  They reportedly dug canals with a-bombs, seriously
polluting several rivers in the process.  They also used a-bombs as a
mining explosive--then sent unprotected workers into the mine only hours
after the explosion.  Please try to refrain from using nukes for anything
other than blowing up people, and I really hope we don't use them for
that purpose either.

-john-

--
==============================================================================
John A. Weeks III        [phone]            [e-mail]
Newave Communications, Ltd.                ..!uunet!tcnet!newave!john

------------------------------

Date: 29 Oct 92 18:18:33 GMT
From: Henry Spencer <[e-mail]>
Subject: Putting volatiles on the moon
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John A. Weeks III) writes:
>> As a method of steering the comets, a few large nukes could give a comet
>> enough of a push to do the job. Also a good usefull way of turning swords
>> into plowshares! ...
>
>... Please try to refrain from using nukes for anything
>other than blowing up people, and I really hope we don't use them for
>that purpose either.

Far more people have been blown up by conventional explosives than by
nuclear weapons.  Should we therefore refuse, on high moral principles,
to use dynamite for construction?  This is silly.
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

------------------------------

Date: 29 Oct 92 17:56:24 GMT
From: Henry Spencer <[e-mail]>
Subject: QUESTIONS: Apollo, Earth, Moon
Newsgroups: alt.sci.planetary,sci.astro,sci.space

In article <[e-mail]> [e-mail] (Wan Ngai Wayne Lee) writes:
>   ... the astronauts passed through a "dead man's zone" during
>   which a descent stage failure could not be solved by using
>   the ascent stage to return to orbit...
>   a. Did this only apply to the early missions or did the "dead
>      man's zone" possibility apply to all of the moon shots?

All of them.  Such zones are also known as "black zones".  In the case of
the lunar landings, as far as I know there was only one:  a descent-stage
failure at very low altitude would not leave enough time for staging and
ascent-stage ignition before the crash.  As far as I know, if they could
get the ascent stage lit and if it stayed lit for a while, they always
had an abort procedure available (although some required CSM cooperation).

>   b. If the descent stage would have failed, would the procedure
>      have been for the astronauts to continue dropping to the
>      surface or attempt an abort to orbit?

Without the descent stage, landing was not possible.  The descent stage
carried the landing gear.  It also had the throttlable engine needed for
a soft landing.  (Making a rocket engine throttlable is not simple and
is done only when necessary; the ascent-stage engine was not throttlable.)
Even if you could land with the ascent stage, you wouldn't have the fuel
to return thereafter.

>   During the Apollo missions, was it ever possible for Earth-based
>   radar to determine where moon-orbiting craft were?  It is my
>   impression that the answer was no...

Wrong, in fact very wrong.  All the precision navigation was done by
Earth-based tracking.  However, this tracking did rely heavily on the
transponders (which, speaking sloppily, basically amplify the received
signal and retransmit it) carried by the spacecraft.  "Skin tracking" --
tracking an uncooperative object by its radar reflection -- was not
practical for objects of that size at that distance, and still isn't.

>   Has the prehistoric "flip" of Earth's magnetic field been proven?

It's about as well proven as it can be, although the geologists are
still arguing about details.

>   What may cause this in the future?

It seems to happen periodically.  Just how quickly it happens, and
whether it is spontaneous or triggered by something, is unclear.

>   Does the Moon has its own magnetic field?  If I had a compass on
>   the moon, how would it behave?

The Moon's magnetic field is feeble and confused.  A compass would not
be useful.

>   In the 1970's, I read that Apollo 12 & 14 ALSEP sensors (ION) picked
>   up what seemed to be a water vapor emission near Fra Mauro.  What
>   would be an alternative explanation for such readings?

Nobody seriously doubts that the Moon still outgasses a little here
and there.  Whether substantial deposits of volatiles still exist in
reachable places is another question.

>   How respectable is the notion that frozen water may exist on the moon
>   and how would such a discovery related to moon's origin & history?

Very respectable, but it would have to have arrived after the Moon's
formation and early volcanic period.  There is considerable suspicion
that volatiles deposited on the Moon by comet impact may still exist,
frozen in polar craters which never get direct sunlight.  Suspicions
have been strengthened considerably of late because radar mapping has
discovered what is probably ice at the poles of Mercury (!).  Flying
a gamma-ray spectrometer in low lunar polar orbit, which would (among
other things) let us survey the entire Moon for near-surface ice, is
a very high priority for lunar scientists.

>   By the way, Arthur C Clarke has put moon water in his 2061 novel.

Lunar water, either as fossil ice or water of hydration, has been a
staple of science fiction for a long time.  It came as a bit of a shock
when Apollo samples showed that the Moon was very thoroughly baked early
in its history, which means no fossil ice and no water of hydration.
Any volatiles on the Moon are more recent arrivals.
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

------------------------------

Date: 29 Oct 92 18:00:38 GMT
From: James Davis Nicoll <[e-mail]>
Subject: Re:Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

    I was noodling around with impact energy estimates for S-T, and
got a value of about 30 million megatons. *IF* the energy were distributed
like a nuke's (Which it wouldn't be,  but maybe it's good enough for my
purposes), you could expect buildings to be  seriously damaged over
an area about 4200 km wide, and windows to be shattered over an area
12,000+ km wide. Fires should extend out to the horizon,whatever
that is in this case. While fallout would be non-radioactive, there'll
be gigatons  of the crap blocking sunlight.

    The crater should be very impressive: ~50 km wide and 25km
deep, although I expect  it wouldn't stay that way  for long.

                            James Nicoll

------------------------------

Date: Thu, 29 Oct 1992 17:03:49 GMT
From: [e-mail]
Subject: Scenario of comet hitting Earth
Newsgroups: sci.astro,sci.space

In article   <[e-mail]>,         Gary Kronk <C09630GK@WUVMD> writes:
>
   [...stuff deleted...]
>
>         WHAT MIGHT HAPPEN IF COMET SWIFT-TUTTLE HIT EARTH
>
   [...stuff deleted...]
> Perhaps it is comforting to know that we are aware of the chances
> for Swift-Tuttle hitting the Earth in 134 years. Maybe sometime in
> the future something could be done to help protect Earth from this
> comet, like a couple of space probes carrying nuclear warheads which
> could destroy the comet if its recovery in 2125 or 2126 reveals the
> threat of collision with Earth still exists.
   [...stuff deleted...]



Just because a nuclear explosion could 'destroy' a comet, does not
mean that the material making up the comet would thereby _disappear_
(conservation of matter), nor would the rubble necessarily not
continue on the same trajectory as it did before being nuked (conservation
of momentum and energy).  A pile of debris hitting the earth at 60 km/sec
could make a mess just as surely (if not as effectively) as an intact comet.
(This is one of the SDI falacies of 'shooting down' ballistic missles.
They be coming down no matter what.  Like the SCUDs - hitting a missle
ain't enough.)


What we have to do is ensure the orbit is a safe one - don't matter if
it's broken apart, just so it misses.  And a small, steady thrust over
a long period of time could be just as effective, if not as spectacular,
as a last-minute explosion.

BTW, other than that minor quibble, the original posting answerd the
question well.

WHH - still here %-)

------------------------------

Date: 29 Oct 92 15:12:01 GMT
From: Brad Whitehurst <[e-mail]>
Subject: Solar Sails
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Frank Crary) writes:
>In article <[e-mail]> [e-mail] (Brad Whitehurst) writes:
>>>Well, so solar sails are just "driven by radiation pressure".  I'd heard
>>>that (as well as solar wind) before.
>
>>    Well, I don't have any numbers, but don't forget the "solar
>>wind" of particles streaming from the sun.  I would think it would
>>have a significant contribution.
>
>The particle momentum is less than 1% that of the radiation pressure.
>However, there is a idea for using it (Zubrin's Magsail): The particles
>are charged, and interact with magnetic fields. In theory, a loop of

    Interesting.  NPR had a bit this AM about the solar sail
"regatta" to the moon.  I didn't listen closely, but they did speak of
using the solar particle wind.  Is this an error on their part, or is
the particle flux in the earth-moon system stronger somehow?
(acceleration in the magnetosphere or some such?)

--

Brad Whitehurst    |   Aerospace Research Lab
[e-mail] |   We like it hot...and fast.

------------------------------

Date: Thu, 29 Oct 1992 17:16:04 GMT
From: Frank Crary <[e-mail]>
Subject: Solar Sails
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Brad Whitehurst) writes:
>>The particle momentum is less than 1% that of the radiation pressure.

>    Interesting.  NPR had a bit this AM about the solar sail
>"regatta" to the moon.  I didn't listen closely, but they did speak of
>using the solar particle wind.  Is this an error on their part, or is
>the particle flux in the earth-moon system stronger somehow?

An error on their part: The radiation pressure at the Earth is of
order P/c = 1.4E3/3E8 = 5E-6 newtons/m^2. The particle pressure
is of order Nmv^2 = 9E6*1.6E-27*5E5^2 = 3E-9 newtons/m^2.

                                          Frank Crary
                                          CU Boulder

------------------------------

Date: 29 Oct 92 17:58:26 GMT
From: Henry Spencer <[e-mail]>
Subject: Solar Sails
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Brad Whitehurst) writes:
>    ... NPR had a bit this AM about the solar sail
>"regatta" to the moon.  I didn't listen closely, but they did speak of
>using the solar particle wind.  Is this an error on their part, or is
>the particle flux in the earth-moon system stronger somehow?

It's an error on their part, and a common one.  A solar sail should use
the solar wind, right?  Except that the analogy isn't valid.  Particle
thrust is minor in the Earth-Moon system like it is everywhere else.
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

------------------------------

Date: 29 Oct 92 16:45:07 GMT
From: Gerald Cecil <[e-mail]>
Subject: Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.space

In article [e-mail], [e-mail] (Josh 'K' Hopkins) writes:
 [ consequences of impact deleted ]
>estimates, but it's important to remeber that as a comet, S/T has a much lower
>mass and is much more fragile than a similarly sized asteroid.  As such, it's
>much less dangerous than an asteroid of the same size.
According to Shoemaker & Shoemaker in ``The New Solar System'', Chap 21
  ``Earth-crossing asteroids are rarely more than 3 km across, [so] most craters
    larger than 60 km [on Earth] probably result from cometary impact.''
But, this is obviously in disagreement with the K/T iridium detection, which implies
an asteroidal origin if extraterrestrial.  The Yucatan impact structure is estimated
to be ~160 km across I recall. They also state that
   ``we suspect that the largest craters on Venus have been produced by comet hits.''
so the atmosphere doesn't appear to help much.  Finally, S/T comes in at a much
higher velocity -- 50 km/s vs 17.5 for an Earth-crossing asteroid (this from
Shoemaker & Shoemaker).  Well actually the vector sum, but still more energetic.
Crater size still estimated at ~20x the diameter of the impacting fragment.
---
Gerald Cecil [e-mail]  919-962-7169
Physics & Astronomy, U of North Carolina, Chapel Hill, NC 27599-3255 USA

------------------------------

Date: 23 Oct 92 02:21:00 GMT
From: [e-mail]
Subject: UFO EVIDENCE VS. Carl Sagan
Newsgroups: sci.space

Marinov and the Jelly Fish

> Robert E. McElwaine B.S., Physics and Astronomy, UW-EC                <
Reminds me of Stefan Marinov of Austria who ran a 3 page ad on pp 48-50 of
New Scientist of 18 December 1986. Marinov had elegant maths to show how
his unique machines worked. His ideas centered around truth, relativistic
physics, gravity and electromagnetism. He had a great deal to say about
prejudiced science and blind scientists -  "jelly fish". It makes great
reading. Several weeks later a brief letter to the editor convincingly
showed the basic flaws in Marinov's science and politely and generously
showed the author to be an eccentric crank.

 It is in fact unfair to compare Marinov with R McElwaine B.S. or indeed
 Marinov's work with R McElwaine's B.S..     Marinov has much more class.
_Marinov to the World's Scientific Conscience_   gives good insight into
 the rare mind of the intelligent misfit. If lateral thinking gives
 results surely if these fruit loops were harnessed to logic they could
 drag productive research into unexpected new dimensions.

 Thank goodness I'm normal. How about you?

                                Lawrie Williams

------------------------------

Date: 29 Oct 92 15:35:26 GMT
From: John Black <[e-mail]>
Subject: What does the "P/" mean in P/Swift-Tuttle?
Newsgroups: sci.astro,sci.space

I've been wondering why the names of comets are prefixed by 'P/'. What does the
'P/' signify?

            John Black.

------------------------------

Date: 29 Oct 92 15:23:59 GMT
From: [e-mail]
Subject: What does the "P/ " mean in P/Swift-Tuttle?
Newsgroups: sci.astro,sci.space

The P/ in P/Swift-Tuttle stands for Periodic. This class of comets includes
all comets with periods less than 200 years (if I recall correctly).

A small point about the possiblity of impact with the Earth - if we take
ST to be about 10 km in diameter and friable in makeup the fact that the
relative Earth-Comet speed at impact would be about 60km/s is worth noting.
I think most estimates for comet-sized objects impacting the Earth assume
prograde orbits - hence the energy involved in an ST collision would be
something like 10 times as much as for a prograde comet of the same size.
This I think could cause a K-T like event.

While there saromany models of what will happen in such an event, ST is such
an oddball comet (n terms of outgassing) that there is noo guarantee that it
will have a makeup like P/Halley. Hence there is much uncertainty as to what
might happen in a direct impact.

Peter Brown
[e-mail]

------------------------------

Date: Thu, 29 Oct 1992 15:07:02 GMT
From: [e-mail]
Subject: What does the "P/" mean in P/Swift-Tuttle?
Newsgroups: sci.astro,sci.space

In article <[e-mail]>, [e-mail] (John Black) writes:
> I've been wondering why the names of comets are prefixed by 'P/'. What does the
> 'P/' signify?
>
>             John Black.

------------------------------

End of Space Digest Volume 15 : Issue 357
------------------------------