> When I said the orbits of the planets and comets were regular, I was
> corrected by the comments that gravational interference from other bodies
> does alter the periods of orbits. What I was thinking when I said that,
> is that without outside interference the orbits are regular and
> predictable - e.g. the earth and moon orbits. I forgot that the orbits
> of comets, which are of comparatively low mass, are easily altered by
> planets.
It is not that the masses of comets are low which allows their orbits to be
easily changed by the planets, particularly Jupiter, it is because their
orbits are often highly eccentric, and can thus pass close to one or more
planets.
> My point in saying that orbits are regular was to say that orbits are
> very much like a pendulum used to drive a clock. Each can be used to
> measure time. YECs have used short period comets to support a young
> earth, which I feel is unreasonable. However, I don't recall ever having
> seen OECs use long period comets as a measure of long ages.
YECs try and use the relatively short lives of short period comets as
"evidence" of a young solar system.
> In my mind, long period comets are a clean measure of millions of years.
> Comet orbits have none (that I can see) of the "assumptions" that YECs
> present to discredit OEC arguments such as radioactivity, speed of light,
> etc. If a comet enters the solar system with a velocity high enough to
> suggest it has been "falling" for millions of years, what YEC argument
> would negate the conclusion that it really has been traveling that long?
In fact as far as I know, no comet has been discovered coming in to the
inner solar system with a hyperbolic orbit (e>1) that has at least not been
perturbed by a planet on the way in. Several comets have been
discovered to have their orbits altered to be hyperbolic by planetary
perturbations, and are thus ejected from the solar system. It would be
reasonable on the basis of comets being ejected from the solar system,
that there would be comets ejected from other star systems, so there
would be a population of interstellar comets. However, the density is too
low for any to have been observed. I don't know the longest period of a
known comet (other than infinity for hyperbolic orbits), but it would be
in the 100,000s or a few million years. YECs would, however, have a
problem with such comets, as they would have to explain how the comet
got into an orbit with a period of say 100,000 years when it was created
6000 years ago well outside the influence of the perturbing effects of the
planets.
> I have been able to accept the suggestion that God created with apparent
> age, but I have never been comfortable with the idea that God would
> create, for example, fossils in primary rocks. Long comet orbits strike
> me at this time as being more akin to fossils than to light from distant
> stars.
One reason the appearance of age argument falls flat on its face is
theological, as YECs have to propose a deceptive God who creates with
the appearance of age WITH A FICTITIOUS AND A REDUNDANT PAST
HISTORY, such as starlight being partially absorbed by dust on its way
to the earth.
> I had some questions re comet orbits/velocities which I didn't see
> answered here, so I asked Tom Van Flandern (website link below). For
> those who might be interested, and with Tom's permission, my questions
> and his answers are copied below.
> Bill Payne
> what is the difference between a hyperbolic and parabolic orbit?
| Both are standard geometric shapes. Both are open. They are
| the open-orbit counterparts of circles and ellipses. Just as
| all circles have the same shape (e = 0) while ellipses have
| a variety of shapes (0 < e < 1), all parabolas have the same
| shape (e = 1) while hyperbolas have a variety of shapes (e >
| 1). [e = eccentricity.]
> Couldn't both be open, so that a comet with either orbit would
> not return to the solar system?
| That is true. Both are always open, escape orbits.
> Aren't all comets gravitationally bound to the sun?
| All *periodic* comets are bound to the Sun at the present
| time. *New* comets (those arriving from the "Oort cloud"
| (which I maintain does not exist) always arrive on bound
But most astronomers do maintain it exists.
| orbits, although only marginally bound. However, the binding
| is so marginal that the tiny impulses these comets get from
| planets are enough to change half these orbits to unbound as
| they leave the planetary region, never to return.
> If one were not, would the only determining factor be the velocity,
> i.e., its velocity would have to be greater than the escape velocity
> from the sun?
| That is true.
> I don't see where the shape of the orbit would affect whether a comet
> was gravitationally bound to the sun.
| Generally, orbits are ellipses. But if a comet receives a
| speed boost such that it goes faster than escape velocity,
| it never returns. Its orbit is therefore open by definition.
| The shape of the path it follows is a hyperbola
| (approximated by a parabola in some cases). Speed determines
| boundedness and shape together. They go hand-in-hand.
> I reviewed your book to see if you said that we have seen a comet with
> a period of 3 million years, and I couldn't find that statement.
| All "new" comets have periods of millions of years. All are
| possibly consistent with 3.2 million years. The more
| accurately the orbit is determined, the closer the period is
| to 3.2 million years. [This property is not obvious. See my
| paper "The Exploded Planet Hypothesis -- 2000" at
| <http://metaresearch.org>, "Solar System" tab, "EPH"
| sub-tab.)
The Exploded Planet Hypothesis has long since been discarded.
I looked at the website, and when I saw the claim that the Cydonia
face on Mars is artificial, I became very suspicious.
> What is the longest period comet we have observed?
| Unbound comets have infinite period. The most loosely bound
| comets have observational uncertainties that overlap
| (unbound) infinite period.
> I would assume that we have seen comets with periods longer than a
> couple of thousand years. Is that correct?
| Yes. Comets with periods less than 100 years are classified
| as "short period". Comets of more than one observed return
| in human history are classified as "periodic comets". The
| majority of newly discovered comets (as opposed to
| dynamically "new" comets) have periods of thousands of years
| or more. Best wishes. -|Tom|-
I thought the criterion for short period orbits was 200 years, but
that's perhaps splitting hairs. It's a question of defining what a
"short period" is.
Christopher M. Sharp
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