For example, today, March 11th, the sun has the same "altitude" or "angle" as September 29th.

The location is another factor. If you’re at a higher elevation, the higher the index will be because you’ll be closer to the high angle of the sun. Lastly, the time of day can be a factor.

If a person stands and looks up at an object, the angle of elevation is the angle between the horizontal line of sight and the object. If a person stands and looks down at an object, the angle of ...