Why the earth's lowest orbital velocity occur at aphelion?

Answer 1

Because that's the way gravity works. If you take Newton's formula for gravitation,

and you're comfortable enough with calculus and geometry to play around with it

for a while, you discover that a body in orbit around a much larger central body

must follow an elliptical path with the central body at one focus of the ellipse, and

that the line between them must 'sweep out' equal areas in equal periods of time.

These facts are exactly two of Kepler's three 'laws'. He got them by analyzing Tycho's

measurements and notebooks of how the things in the sky actually move, but once

the idea of gravity came around, it could finally be shown mathematically why things

must act that way.

That bit about sweeping out equal areas in equal periods of time ... that means that

when the orbiting body is closer to the central body, it has to move faster, and when

it's farthest from the central body, it has to move slowest.

Answer 2

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