How do you calculate obliquity of ecliptic?

1 Answer
May 19, 2016

Imagine that you are an equatorian (in Brazil), standing at noon on summer solstice (about June 21). Then, tan (obliquity) = h/l, where h is your height and l is the length of your shadow.

Explanation:

At a solstice noon, the angle of incidence of light rays from the Sun upon the equator is (almost) obliquity = ${23.4}^{o}$.

If Y is your head, U your foot and US is shadow, $\tan \angle U S Y = \frac{Y U}{U S}$, and you subtend #angle USY = obliquity, at S..