Willy Leenders <[EMAIL PROTECTED]> writes: > The equation of time has two causes. The first is that the orbit of > the earth around the sun is an ellipse and not a circle. The second > is that the plane of the earth's equator is inclined tot the plane > of the earth's orbit. Please can anyone explain me the second cause > so that I can conceive it. I am not a astronomer!
I have given this question a lot of thought, but I realized when I was asked about it a few days ago that I am still not satisfied with my answer. I have tried to explain it in detail on my page "http://www.ipp.mpg.de/~Arthur.Carlson/sundial.html";, but that isn't the intuitively obvious answer we would all like to have in order to claim that we "understand" the effect. If I had to answer in one sentence, I might say that the effect arises because the sun moves against the stars (in the Ptolemaic sense) on a circle (the ecliptic) that differs from the coordinate system we use to define time (the equatorial plane). You can see that it is a "mathematical" effect, as opposed to the "physical" effect of the eccentricity, by considering a planet that does not rotate, so you can place the poles anywhere you want. The hour angle of the sun during the course of the year, except at the solstices and equinoxes, will depend on your choice. > You can do it in Dutch (for preference), in French, in German or in English. I can offer you German, if you have trouble understanding the English. Art Carlson
