'Tis the Week to Explain the Solstice

The Winter Solstice will occur at 3:44 am MST on Wednesday, December 21. It always amazes me at how many adults do not understand the cause of the seasons, or why the length of day varies throughout the year. A significant percentage think that the seasons are caused by Earth being closer to the Sun in the summer, and farther in the winter. Actually, Earth is closest to the Sun in early January and farthest in early July! As for the length of day, I think many do connect it with Earth's tilt, but few can really explain the dynamics. Try this sometime this week . . . Give your students a few minutes at the start of class to answer two questions on a slip of paper. Have them hand them in, and then use the resources below to explain the answers.

1. What causes Earth to experience seasons?

2. Why is the length of daylight longer in the summer and shorter in the winter?

CLICK HERE to see an animation courtesy of the Santa Barbara City College Dept. of Physics and Engineering. I project the animation onto a big screen and use it to explain the solstice (and its relationship to the length of daylight). CLICK HERE for more information about the solstice. CLICK HERE to see another animation (courtesy of Prentice Hall). CLICK HERE to get sunrise and sunset times for your city.

CAUTION: Animations and diagrams often depict the shape of Earth's orbit as being more elliptical than it really is. If you were to draw our orbit on the board, it would look like a circle. Here is another resource that may help. Once the page open, the diagram titled "Eccentricity" is a good one. This Hours Explorer is pretty slick too! (Thanks, Rick)

Merry Christmas!