Questions and Suggestions
Jan 12 - Pluto is weird.
a question from Charles: "[I] have observed in two of the sources I’m reading in that all our planets (except the disputed Pluto) are apparently coursing around in the same plane and that Pluto’s course is 17 degrees off that plane. If my sources are correct what are the forces that have caused that to be?
Bob: "The answer (or the theory until disproven) is a two-parter.
The first weird thing about Pluto is that it spins on a horizontal axis like
only one other planet (Uranus, tilted at 8 degrees above horizontal). We think
this was caused by a single impact which also knocked the Charon chip off
the old block.
The orbit is tilted at 17 degrees compared with the rest of the solar system.
Even though Neptune never gets closer than a one-fourth orbit to Pluto, we
think that Neptune has forced, and is still forcing Pluto into a more elliptical
and more tilted orbital plane. Letting AU stand for the Earth-Sun distance,
Pluto comes within 30 AU but then flies out to 50 AU at aphelion. It rises
8 AU above the plane of the solar system and sinks 13 AU below it. Pluto and
Neptune years have settled into a 3:2 resonance, Neptune doing three laps
for Pluto's 2.
The image that comes to mind is the cartoonish one of the big bully holding
off the feisty little guy with a straight arm on the forehead, while the little
guy takes wild roundhouse swings that move the air and become more erratic
with fatigue.
These anomalies are better understood in the context of the other minor planets
discovered outside of Pluto, but in the same neighborhood. These Kuiper Belt
objects are in the same resonance with Neptune and their orbits can be tilted
by as many as 20 degrees. Neptune and Uranus are blamed for tossing these
objects out to spatial Siberia, whilst, Jupiter had enough gravitational zing
to expel some completely away." source: Dava Sobel, The Planets.
Winter Solstice Questions
1. Is winter solstice the shortest day? Yes.
2. Is winter solstice the day of latest sunrise? No? ... of earliest sunset?
No?
The earliest sunset occurs a couple of weeks prior to solstice and the latest
sunrise a couple of weeks after. This is due to the fact that our clocks are
set for an average 24-hour day, and the fact is that the Sun runs slower and
faster than average at times. The discrepancy is called the “Equation
of time,” and is caused mainly by two factors: the 23 degree tilt of
our axis and the elliptical (not circular) shape of our orbital path around
the Sun. For more info try the link below.
http://en.wikipedia.org/wiki/Equation_of_time
Moon Question: Does the Moon keep the same
face toward Earth? Answer. Yes, it more or less does. The more or less part
is called the libration, where we get a glimpse of a little bit of the far
side at times. See “libration” in the glossary.
Why the same face, Moon? In cosmic history, it probably wasn’t. The theory is that the Moon’s rotation has come into resonance (harmony, if you will) with that of the Earth. We think that the changing tides on Earth are the cause, and of course, we know that the Moon is mainly responsible for those, but those tides have had a reciprocal effect.
Someone asked about the 3 laws of Kepler.
1. The planet orbits are ellipses.
2. If one segment of an orbit takes an equal time to traverse as another,
then the wedges connecting the extreme points back to the Sun have equal areas.
3. The square of the orbital period is proportional to the cube of the distance
out from the Sun. (i.e. farther out means longer "year")
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