How fast is Earth moving?

Hello, all. I have a question.

How fast is Earth moving relative to the sun?

Does the speed change regularly? If so, in what way?

Thanks.

--Johnny
http://barelybad.com

On Tue, 2 Nov 2004 16:02:17 -0600, "Johnny"
wrote:

Hello, all. I have a question.

How fast is Earth moving relative to the sun?

Does the speed change regularly? If so, in what way?

If the Earth's orbit were circular, the speed would be constant (in
physics it's called uniform circular motion), which you could
calculate using nominal values for the orbital radius (called an
astronomical unit), pi, and the numbers of hours in a solar year.
This still provides a reasonable approximation for many applications.

But we know the orbit is elliptical with the Sun at one focus. By
one of Kepler's laws, we know that the speed is fastest at perihelion
and slowest at aphelion. By the principle of continuity, we know the
speed varies continuously from one to the other and then back again
over the course of a year.

One of the ways this variation manifests itself is the analemma
(equation of time) since the Sun does not return to high noon in the
sky in the same amount of time each day (24 hours is just nominal).

Plug a few of these terms into google and see what you get.


Remove the del for email

Barry Schwarz wrote:

But we know the orbit is elliptical with the Sun at one focus.

Close enough for the purposes at hand, but it's worth pointing out
to the original poster that, more properly, it's not the Sun which
resides at the focus of the ellipse. At the focus, in fact, is the mass
center of the Earth/Sun system, also called the barycenter. Of course,
Earth contributes such a negligible portion of the total mass that the
barycenter is practically at the Sun's own mass center.

-Mark Martin