An analemma is exhibited over a year because the Earth is tilted on its axis and it orbits the sun in an ellipse.The Earth is not the only planet to have an analemma. Of the eight planets in our solar system ( far reaching Pluto is now a sub-planet but also has an analemma), six of these exhibit the right orbital characteristics for the sun to form an analemmic curve throughout the planet's solar year
Once it was proved that the Earth was a circular, globes started to display the figure eight of the analemma.
Also because of the tilt and the orbit, the Equation of time is also comes into play. To grasp this concept, think of the difference of time, at a given point in time, between a Sun Dial and a Clock. The difference can be up to eight minutes.
At certain times of the year, variations of these observed concepts are the reason that seasons do not start exactly on time.
All this to say, that nothing is on time.
