Caption: A diagram illustrating how to determine the altitude of the north celestial pole (NCP).

Features:

1. This is a cross-sectional view of the Earth.
2. The Earth's axis is extended to the north celestial pole (NCP) and the Earth's equator is projected outward to the celestial equator.
3. The NCP and celestial equator are infinitely remote, and so any lines parallel to lines going to these things also go to them.
4. L is value of the latitude of a general observer on the Earth's surface. It's NOT 45° or any specific angle---it just looks that way.
5. The observer is tiny and so the Earth's surface to him/her is an infinite plane cutting the celestial sphere in half---the cut line is the horizon.

Credit/Permission: © David Jeffery, 2013 / Own work.
Image link: Itself.
Local file: local link: ncp_altitude_circumpolar.html.
File: Celestial sphere file: ncp_altitude_circumpolar.html.