Paths of the Sun
Using meridional altitude and the geometry of the ecliptic one can specify a procedure to draw the paths of the sun for any latitude on the earth. Below are instructions to draw the path of the sun at either equinox when the sun is on the celestial equator. This path reflects the average location of the sun in the sky. There are also directions for drawing paths of the sun for either solstice. The solstices are the extremes of location of the sun in the sky.
One should begin with a horizon diagram and follow the procedure below:
- Draw in the Appropriate Celestial Pole.
This allows one to take into account the observer's latitude. If the observer is in the northern hemisphere the NCP will be on the observer's meridian above the north point at an altitude equal to the observer's latitude. If the observer is in the southern hemisphere the SCP will be on the observer's meridian above the south point at an altitude equal to the observer's latitude.
- Draw in the Celestial Equator.
The Celestial Equator is 90° away from both celestial poles. Thus, it should intersect the observer's meridian at an altitude of 90° minus the observer's latitude. The Celestial Equator should be drawn from the east point on the horizon, cross the observer's meridian, and connect to the west point on the horizon. Drawing the portion of the Celestial Equator that is below the horizon is very useful for latitudes near the poles. (Note that this step needs to be slightly altered at the north and south poles where the Celestial Equator is on the horizon.)
- Notate the Equinox Path.
Realize that the sun in on the Celestial Equator for both equinoxes – so we have already drawn the equinox path – it is the Celestial Equator. So simply write equinox path near it. This is the sun's average path for this latitude during the year.
- Draw in the Solstice Paths.
The sun is 23.5° above the Celestial Equator on the summer solstice and 23.5° below on the winter solstice. These paths need to be drawn as coaxial circles (ie they have the same axis through their centers and never intersect).
One can think about these paths as rungs of a slinky. The equinox path is the middle rung while the solstice paths are rungs on the top and bottom of the slinky.