# Is there a term for the vertical elongation of a planet?

1. May 4, 2010

### dotancohen

Is there a term for the vertical elongation of a planet? This would be the angular distance above the horizon that a planet appears at the instant the sun sets, or in mathematical terms it would be:

x=elongation
theta=angle between the ecliptic and the horizon

"vertical elongation" = x * sin(theta)

2. May 4, 2010

### dotancohen

Note that the formula assumes that the planet actually lies on the ecliptic, which of course is rarely the case. But I use the formula to illustrate.

3. May 4, 2010

### SpiffyKavu

Yes indeed, such a word exists. If a sphere is elongated along its semi-minor axis (vertically, in this case), then it is known as a prolate spheroid. This is opposed to a oblate spheroid, in which the sphere is elongated at its equator.

So to answer your question: "prolateness", I suppose would work. And the dictionary confirms that it is a word.

4. May 4, 2010

### dotancohen

Thanks, SpiffyKavu, but I think that we are using different definitions of "elongation". I am using "elongation" in the sense of angular distance from the sun:
http://en.wikipedia.org/wiki/Elongation_(astronomy)

I do not refer to a physical feature of the planet's material, but rather the planet's position in the sky relative to the sun. I apologize, I thought that the definition would be clear here from the context. In fact, I did not even think of the other definition.