Seasons is a Flash Animation. If you don't see the animation after clicking the link above, or are not sure you have Flash installed, please see the FAQ / Help pages. Note, the animation assumes you are an observer in the northern hemisphere (sorry to all of our friends below the equator!). For an observer in the southern hemisphere, the seasons would just be reversed.
Please note the scale of the sun, earth, and the orbit of the earth are not accurate, but have been shown as such to emphasize what is going on!
Seasons has a lot going on. There are three main "panels" to watch:
Orbit Panel: This shows the earth as it orbits, or revolves around the sun. As it goes through its orbit, the date and seasons display in text below the action. Note the and the location of the Earth relative to the Sun on those days.
Declination Panel: This panel shows the declination of the sun as it goes through its orbit. Note that, unlike the "fixed" stars, the declination of the sun changes throughout the year. Click on the ? next to the panel for more information.
Intensity Panel: This panel is designed to show you how a patch of sunlight gets spread out and more concentrated throughout the year. This is one of the main causes for the changing seasons (not how close we are to the sun!). Click on the ? next to the panel for more information.
Some things to look for and some notes about the seasons in general:
Winter: This is where the animation begins. Notice the date, and the location of the Earth with respect to the sun. Winter in the Northern hemisphere occurs when we are close to the sun. Notice how spread out a patch of sunlight on the ground is due to the low altitude of the sun.
Spring: Roughly 1/4 of the way through the orbit. Notice the declination of the sun. Since the sun lies on the celestial equator, we are at an equinox -- day and night have equal length. Also, the sun will rise due east and set due west. Notice the patch of sun is becoming more "concentrated."
Summer: The sun has now reached its highest declination. We are most distant from the sun. Notice that the patch of sun on the ground is most concentrated.
Autumn: The earth has now gone 3/4 of the way around the orbit. The sun is now getting lower in the sky, and is again on the celestial equator -- the Autumnal Equinox. The patch of sunlight is getting more spread out.