Talk:Earth radius

I believe that in the comment where A is the authalic surface area of Earth, the word authalic is not needed. As the term means equal area, the "authalic surface area" of the Earth is identical to the surface area of the Earth! Making the distinction between the two may confuse people into thinking that they do not really understand what authalic means. If anything, make it clear A_r is the authalic radius.

Question: Why is this comment

Note: Earth radius is sometimes used as a unit of distance, especially in astronomy and geology. It is usually denoted by RE.

part of the "Volumetric radius" section?

Should it be perhaps "Earth volumetric radius is sometimes used...", or does this comment refers to the general case, situation in which it should be moved somewhere in the main text?

Radius vs. Sea Level

"The radius of Earth (or any other planet) is the distance from its center to a point on its surface at mean sea level." This doesn't seem right. Why is the mean radius of a planet exactly the sea level? The sea level of the earth is rising, does this mean the radius of the earth is increasing too? Why would the melting of the ice caps cause the land to rise? Anyone have a cite? -anon

Radius of curvature

I have changed the formula for Rc near the end of this section to reverse M and N, since when traversing along a meridian (with alpha = 0, i.e. facing North) one is moving along "M" the meridianal radius and when moving (e.g at the equator) eastward (for alpha = + 90 degrees) one is moving along "N" the radius of curvature in the prime vertical. JimC (C&B) 17:57, 7 January 2007 (UTC)

You just described it right——facing north-south the RoC = M, while facing east-west = N——so cos(0)M = M and sin(90°)N = N, which is how it was (your change went and inverted it!

Whoops, okay, I see the problem: Presenting it with MN as the numerator cancels and reverses the placement of M and N in the denominator. I've changed it to make it clearer. P=) ~Kaimbridge~ 15:21, 8 January 2007 (UTC)

ERROR?

On this page the polar radius is derived as being larger than the equatorial radius. Please check this derivation. —The preceding unsigned comment was added by 216.59.226.224 (talk) 04:48, 25 April 2007 (UTC).

What do you mean, a (equatorial radius) = 6378.135 and b (polar) = 6356.75? ~Kaimbridge~10:49, 25 April 2007 (UTC)

Regarding the values a and b, I think it should be corrected and precised as follows: a=6378.137 km (according to GRS80 and GRS84) and b~= 6356.752 km (as a derived value). Gil