1. The problem statement, all variables and given/known data Which is the angle between the ecliptic and the horizon in the moment that the point of Aries is hiding for an observer whose position is 18 degrees north? 2. Relevant equations None 3. The attempt at a solution The first thing I have tried to is to do a drawing of the situation: here it is: http://postimg.org/image/dh3xkvipv/ Then I went to the software stellarium and I put the observer exactly at 18 degrees north; found a star with zero right ascension and I went forward in time until the star had height zero; then, I measured the difference between the north and the ecliptic and I got about 84 degrees: http://postimg.org/image/vs1i12dwp/. If I calculate 90-23.5+18 I get 84.5, which is similat to the 84 that I got with the aproximate calculus at stellarium, but I don't know how to justify it. Can anyone thell me if there is a way to calculate the angle between the ecliptic and the horizon in the moment that the point of Aries is hiding for an observer whose position is known? Thanks for reading.