Since the diameter of the earth is 8,000 miles, the center should be 4,000 miles straight down from anywhere. Howerver, the earth isn't a perfect sphere, so there are minor differences. The earth is flattened at the poles (like George Bush), so that's the place to start if you're planning on going there.
No, the sun is located at one of the two foci of Earth's elliptical orbit, not in the exact center.
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liquid iron
Core
Earths gravity acts on everything from its center of gravity to everything else's center of gravity.
gyudryuj
The Earths crust is approximately 650 km deep.
2900 km
A fault.
There is no exact radius of the Earth, but the average is 3,959 miles or 20,903,520 feet. The Earth is rotating on it's axis and because of this rapid rotation the Earth's poles tend to flatten. Which makes the radius from the center to the equator larger than from the center to the poles.
People are (so far) not able to get very deep inside the Earth, so there is not that much variation, however, the closer you get to the center of the Earth, the less you would weigh. At the exact center you would be weightless.
The equator.