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On Thu, 20 Jan 2000 you wrote:
> 1. What are the observable/measureable gravitational phenomenom of
> passing through the space between two heavenly bodies? Like the
> effects of lunar tides, what does the field between the attractive
> bodies look like? Is there some kind of spillover between gravity
> wells? Also, what would the gravitational fields look like when the
> planets line up in May?
Gravitational forces add together. For instance, if you were to pass
between the Earth and the moon at the right distance, the moon will pull
you one direction, the Earth will pull you the other, and gravity will
cancel out. There is a concept called the gravitatinal potential, which
is a measure of the strength of gravity. If you have seen pictures of
"dents" in space caused by the sun (usually in bad graphics that make it
look like the sun is on a sheet of graph paper), this is a way to picture
the potential.
With regards to any "spilling", this can happen when stars are
close together. If one star starts to expand, it may reach a size where
the gravity from its companion star pulls on the gas stronger than the
parent star's gravity, and the gas will then fall onto the companion star.
As for the planetary alignment in May, the force of gravity falls
off like the square of the distance from a planet. So, if you double the
distance from a planet, the force of gravity is four times weaker. The
other planets are so far away that their gravity is puny. If you are
standing next to a brick wall, the force of gravity of the wall is
stronger than that of the other planets in the solar system. So, if
you stand next to eight brick walls, you know that the gravity is still
not noticeable. The same is true of the gravity of the other planets in
the solar system - whether they are aligned or not aligned makes no
difference on a day-by-day basis. For more on the planetary alignment,
see:
http://www.sunspot.noao.edu/PR/alignment.html
> 2. Since gravity deflects light, is there any basis for universal
> gravitational effects contributing to the perceived "red shift" of
> distant stars?
It used to an argument that the redshifts we see in distant objects were
caused by gravitational redshifts rather than the expansion of the
universe. In fact, for some objects (white dwarfs, neutron stars, and the
disks around black holes) this gravitational red shift has been detected.
But recently we have seen that the distant galaxies with redshifted light
are made of normal stars, and these stars are moving around their galaxies
at speeds typical of nearby galaxies, which means that the gravitational
field in these galaxies is not strong enough to cause a noticeable
redshift. So, the light we see from distant galaxies and quasars is
redshifted due to the expansion of the universe, and not due to gravity.
By the way, gravitational redshifts are not caused by gravity bending
light, but by the fact that for light to escape from a gravitational
field, it has to give up energy. The wavelength (and therefore color) of
light is determined by the light's energy. As it loses energy, it becomes
redder.
Thanks for writing!
Sincerely,
Kurtis Williams
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