Today we began both a new week and a new month - the shortest month of the year but just a day longer. This month, as you may know, has an extra day due to it being leap year. I mention this because this is very relevant to this section of the Earth in the Universe unit.
One of the concepts being covered is how the Earth revolves, or orbits around the sun in a slightly elliptical path.
This is what I explained to the students: it takes about 365¼ days to make a complete orbit around the sun each year. This causes a buildup of time and if isn't accounted for, at some point the calendars would be so messed up as to being useless! For example, the calendar can state that it is the month of July but we can have snow and cold temperatures.
Therefore, every 4 years we have a leap year in which an extra day (¼ + ¼ + ¼ + ¼ = 1 whole) is added to the month of February, it being the shortest month. Since this year is a leap year, it is even more meaningful.
After we reviewed the notes, I proved that seasons are not based on the distance of the Earth from the sun but the relative position of the axial tilt. When a hemisphere (northern or southern) is tilted TOWARDS the sun, it is summer there and winter in the opposite hemisphere.
How was it done? I had a powerful spotlight with a halogen bulb and a globe. I placed a piece of masking tape at the first latitude line north of the equator and labeled it Northern Hemisphere and drew an arrow pointing left to show that the Earth spins in a counterclockwise direction. I did the same for the southern hemisphere and then repeated the process on the exact opposite side of the globe.
To have a basis for comparison, I took an initial temperature reading using a non-contact IR thermometer and had the students record it (I also recorded it on the board). Then, I turned on the spot light and shined it for a minute at the globe with the northern hemisphere facing away. This represents winter in the northern hemisphere (which is the season now) and summer in the southern hemisphere. After a minute, I again took the temperatures of both and recorded them. The data show that the southern part of the globe, the part that received more direct light, had a higher temperature than the hemisphere (north) that received less direct light. I repeated it by turning the globe around to do summer in the north and winter in the south. Again, the results were the same! Here is a slide show of what I did:
I then wanted to give one more proof so I went to the Weather Channel's website and showed the temperature contrasts from Green Bay, WI contrasted with Sydney, Australia. Below is a screen capture of both......
Then, I did another contrast with some real extremes: Fairbanks, AK and Alice Springs, Australia:
As an addendum, I talked about the Coriolis Effect. It causes wind patterns and water (sometimes) to drain either clockwise or counterclockwise depending upon whether one is in the northern or southern hemisphere. In small bodies of water (such as a sink) the effect is much smaller. But, I made a brief video to show it.