Have you ever seen this "figure 8" on a globe and wondered what it is?
It is simply this: if you could record the position of the sun in the sky at the same time every day, let’s say sometime around noon, you would notice that the sun takes a rather strange path.
You might notice that at certain times throughout the year the sun's position not only varies higher and lower (North and South) as you would expect with the change of the seasons, but also slightly east and west.
This figure-8 path that the sun makes in the sky is called the analemma. On some days you might notice that the sun is not in the sky where, according to the time on your watch, you would expect it to be.
The difference in time between what your watch reads and the position of the sun (clock time vs. sun time) is called the Equation-of-Time.
If you are in the northern hemisphere and the sun’s position is to the east of where your watch indicates it would be, the Equation-of-Time is negative. If the sun is to the west, the Equation-of-Time is positive.
Why does the sun take this strange path? There are three reasons and they are completely independent from each other.
1. The Earth is tilted on its axis 23.5° in relation to the plane of its orbit around the sun.
2. The Earth does not orbit the sun in a circle, but in an ellipse.
3. The apse line of the ellipse does not correspond with the solstice.
It is simply the sum of these three effects that causes the analemma. With the aid of a few diagrams and animations, the analemma can be readily understood.