- #51

- 302

- 26

Let's imagine that the observer is on the equator, and that he somehow sees the intersection of the celestial equator with the horizon. One intersection point will lie exactly east, and the other exactly west of the observer. That' easy to visualize.

Now, let' see what happens a day when the sun's declination is -for example- +15 degrees. The sun's path will be (approximately) a small circle to the north of the celestial equator, keeping with it, at every point, a distance of 15 degrees measured along any great circle perpendicular to the celestial equator. In the case of the 'equatorial observer' he might -magically- see the circles of right ascension, and -because of the privilege of being sited in the equator- the circle of his horizon will coincide with one of those circles of RA. Hence, at sunrise or sunset, he will see that the point where the sun crosses the horizon deviates 15 degrees to the north, measured from the exact east and west points...