The Reasons for the Seasons:
How the Earth and Sun interact to Create Seasons

Incoming Solar Energy

Instructions can be found at the bottom of the page. Or you can watch this short mp4 explanation.

You set the latitude and time of year and the incoming solar energy is calculated throughout the day. The red curve represents the calculation for the conditions set by the left menu bars, the blue curve represents the calculation for the conditions set by the right hand menu bar.

Questions:

1. Set both the right and left hand cases to January 21, at a latitude of 42N. Hit calculate - you will see only one curve as the two cases are exactly the same. Now, set the left hand side to February 21, and keep the latitude at 42N, hit calculate and answer the following questions:

2. March 21 is often the first day of spring in the Northern Hemisphere and is called vernal equinox. Set the date to March 21, and the latitude to the South Pole (90S) for both cases, and hit the calculate button. You will see a plot of the incoming solar energy at the top of the atmosphere. On this day, the sun is just sitting on the horizon at the exact South Pole, so the incoming energy is very small because the low angle. Now select another latitude (e.g 60 S) and 'calculate'. Describe the incoming energy at this latitude, on this day. On March 21, the sun is directly overhead at the equator (0 degrees), so the equator should have the greastest incoming solar energy at noon. Use the activity to try and confirm this statement.

3. Now change the date to June 21, the summer solstice, and compute the incoming solar radiation at 80 N, and answer the following question.

Continue

Instructions

This chart plots the incoming solar energy at the top of the atmosphere (no absorption by the atmosphere). You can do this calculation for two locations at once. Select a month, day and latitude from each scroll down menu, and click on calculate. The red curve represents the calculation for the conditions set by the left menu bars, the blue curve is the result for the right hand case.