Re: Possible evidence for Stone Age (Clovis) Cosmic Catastrophe?

On Sun, 06 Nov 2005 11:42:39 GMT,
nospam@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:

>Apparently on date Sat, 05 Nov 2005 18:52:18 -0800, Tom McDonald
><tmcdonald2672@xxxxxxxxxxxxxxxxxxx> said:
>
>>nospam@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
>>> Apparently on date Fri, 04 Nov 2005 16:09:13 -0800, Tom McDonald
><snip>
>>>
>>>> Here is a list of comets named after their human discoverers.
>>>>You will often see comets named Linear X, or SOHO Y; but these,
>>>>and some others, are the names of comet-hunting observatories,
>>>>not individuals:
>>>>
>>>>http://www.comethunter.de/discoverers.txt
>>>
>>>
>>> Yes I realise this. I also realise that most of these people are finding the
>>> comets by looking at SOHO images of the sun - which appear online somewhere or
>>> other. They find objects very near the sun in the images and these are,
>>> presumably, comets.
>>>
>>> These are essentially not relevant to the risk of impact on earth, even less so
>>> than the trillions of comets up out there which don't orbit into the inner
>>> solar system. At least the latter have some prospect of being pitched down
>>> sunwards at some future moment.
>>
>> I would prefer that you mark your snips. In this case, you cut
>>the following bits in quotation marks without comment. (Of
>>course, if you don't have any comment on a particular bit of a
>>post, there is no need to address it. Courtesy and honesty
>>suggest it's best to make note of it when you cut something
>>unaddressed.)
>
>Old school snipping, and to be honest, while I can find loads of netiquette
>pages that give me no requirement to mark snips, I recognise there are probably
>also pages that add one.
>
>Suffice to say I have never felt the need to explicitly mark snips and not
>doing so it not meant to be an insult or anything.
>
>I didn't address your original text because the post was already pretty long,
>and I figured I'd made my point and didn't want to overdo it. It clearly wasn't
>an attempt to dodge the notion of "comets are common" as I am addressing that
>head on with my "(relevant) comets are quite rare" assertions.
>
>But I shall address it now.
>
>> "These, of course, are in addition to the many comets known
>>from long ago.
>
>The problem with this is most of the comets that we know about today *are*
>comets from long ago.

Once again you suffer from a short-term time scale. The effective
lifetime of a super comet is of the order of 30,000 to 50,000 years.
After that all that is left is a diminishing cloud of surviving small
rubble.
>
>Many of the periodic comets in the list on
>http://www.cometography.com/
>have periods that are quite large and they are judged to have been cycling
>around their orbits back into the past, although obviously it is hard to find
>anything to prove this unless you can identify a specific comet from a specific
>description.
>
>If you follow the links to 1P, which is Halley's Comet, you can find the
>historical references to it, which go back to Chinese and Babylonian
>astronomers. We think the comet was present back then rather than some other
>comet with the same "fit" to the descriptions, but there is some speculation.
>
>Assuming this is the same one, we can infer that this same comet has appeared
>to mankind 30 times, it's probable that some visits were remote, i.e. earth was
>in a bad position to view the tail, but most were ok and would have been
>regarded as a different comet each time up until Halley's day.
>
>>Comets are not uncommon; and IIRC, they frequently
>>have orbits relatively well aligned with the plane of the solar
>>system. And, of course, the gravitation of Jupiter and Saturn can
>>alter a comet's orbit so that it becomes an Earth orbit crosser."
>
>Actually, this is not the case. Please look at the list of periodic comets and
>notice the last figure in the table. This is the inclination. It describes the
>angle between the plane of the orbit of the comet and the plane in which the
>planets and asteroids basically reside.
>
>You'll see that only a couple are close to the ecliptic, 1.3 and 1.4 degrees
>respectively. None are inside one degree, and the rest are arbitrarily out to
>180 degrees (which works the other way and is effectively a small inclination
>with the orbit going the other way round the sun to everything else*). There is
>a trend towards the ecliptic, I suppose because the usual reason a comet exists
>in the first place is because it has been influenced by something that was, in
>turn, influenced by a planet and these lie on the ecliptic.

It is amusing to try playing with the orbit viewer in
http://neo.jpl.nasa.gov/orbits/
>
>However, you can see that a few degrees at least is involved for virtually all
>these comets and, because of the way an orbit works, looking at the orbit edge
>on, coming from high and right of the sun, the plane of the comet's orbit
>crosses the plane of the ecliptic as the comet passes the centre of the sun as
>observed from the side, dips below the ecliptic by some amount while passing
>perihelion to the left, so to speak, and then rises on the return pass through
>the centre of the sun on the other side, and goes above the ecliptic from that
>moment on.

But these orbits precess http://star.arm.ac.uk/~aac/zetataur.html
"Precession bringing orbits to intersection with Earth or Mars
[***] is not just relevant from the point of view of meteors being
detectable. The orbits of asteroids and comets can also be
brought to Earth intersection by planetary precession, of
relevance to the Earth impact hazard ."

It is this precesion which brings periodic episodes of bombardment as
the plane of the earth's orbit crosses over that of the comet's. This
is the mechanism at the heart of the astronomical theory of coherent
catastrophism.
>
>Here's a picture to clarify that: http://tinyurl.com/74rs7
>
--- snip ----



Eric Stevens

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