# Tag Info

9

Each time Halley's comet passes us, we can make a pretty good estimate of its current orbit, and determine how close it will get to the massive bodies of the solar system like Jupiter, Saturn, Uranus, or Neptune on its next orbit. We can make good estimates of gravitational perturbation effects, and thereby know where to look for it. In fact, astronomers ...

-3

You guys are over thinking this simple question. All of these answers are based on thoughts, and cannot be answered based on evidence. This is because 1. Space has no gravity, 2. we do not have a tube thats big enough to make light spin around it many times till gravity has effect on the photon (assuming the photon doesn't lose its charge), and 3. we have ...

4

It is simply not true that gravity can only interact with mass. Rather, any long-range spin-2 force interacts with all energy-momentum equally, and it source is the stress-energy-momentum tensor. That is one way to state the equivalence principle. Note that a massive object in its own rest frame has an associated energy $E = mc^2$, which under ordinary ...

1

If photon is mass-less and gravity can interact only with matter, then how gravity can alter the trajectory of light? The second part of your "if" clause is incorrect. It's mass-energy, not just mass, that gravitates.

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I have just stumbled across site. It looks to be a good site for such a discussion. However, a five minute scan shows that the papers by Feng and Gallo (F&G) have not been studied thoroughly, so that a lot of ‘opinion’ is included where ‘fact’ would be preferable. The original question is biased; for a start, it doesn't ask for arguments for and ...

0

5/2013 I was thinking: If one googles the question - you get back earth answers: cheetah, cars, airplanes. I wanted to know in the universe. I was thinking about the "thought experiment" of a ladder moving at light speed that contracts enough to fit into a too small garage. I reasoned if there is NO macro mass (like a ladder) in the universe that ...

7

Why doesn't the sun pull the moon away from earth? Short answer: Because the Moon is much closer to the Earth than it is to the Sun. Longer answer: The gravitational force exerted by the Sun on the Moon is more twice that exerted by the Earth on the Moon. So why do we say the Moon orbits the Earth? This has two answers. One is that "orbit" is not a ...

0

I agree with Adrian's answer. If you look at the moons orbit, in a very real sense it orbits the sun maybe more than it orbits the earth. The Earth/Moon system orbits the sun at 30 KM/s, the Moon orbits the earth at about 1 KM per second. Both orbits are reasonably eliptical. The entire solarsystem orbits around the center of the Milky-way, so ...

2

The Moon is in orbit about the Sun, much as the Earth is. Although this is not the usual perspective from the Earth, a plot of the Moon's trajectory shows the Moon in an elliptic orbit about the Sun. Essentially the Earth, Moon, Sun system is (meta) stable, like that of other planets orbiting the Sun.

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