This lesson will help to explain why we experience different seasons. First, have the students get in groups to discuss the cause of seasons. For example, why does it get colder in the winter and warmer in the summer? In fact, the seasons are caused not by the distance between sun and earth changing but by the orientation of the sun and the earth. In other words, the seasons are caused by the fact that the earth is tilted so that the sun shines on different parts of the earth during different seasons. On December 21, (the winter solstice for the Northern Hemisphere), the sun is shining the furthest south of the equator it will ever shine. This is our shortest day of the year; there is the least amount of sunlight. It would be expected that the sun would rise the latest on that day and set the earliest. On June 21, (the summer solstice for the Northern Hemisphere), the sun is shining the furthest North of the equator it will ever shine. It is the longest day of the year; there is the most amount of sunlight. It would be expected that the sun would rise the earliest on that day and set the latest. On September 21 and March 21, the autumnal and vernal equinoxes respectively, the sun is shining directly on the equator; therefore, the amount of sun light is 12 hours. In other words, the length of day and night is exactly equal all over the world. This lesson will also show whether our expectations about the sunrise and sunset times for the winter and summer solstices are true.

In the Philadelphia Inquirer weather section, the times of sunrise and sunset can be found for each day. This data can also be found at the web site: http://www.weatherimages.org/interactive.html#sunsetrise

solstice

vernal equinox

autumnal equinox

(Sample data is shown on the attached sheets.)

1. Look in the newspaper or on the computer to find the sunrise and sunset times for a particular day(s) that the teacher asks.
2. Graph the sunrise and sunset times on the y axis and the dates on the x axis.
3. Note that June 21, the date of most sunlight is not the date of earliest sunrise and latest sunset.
4. Note that December 21, the date of least sunlight is not the day of latest sunrise and earliest sunset.

Have the students turn in their data and graphs.

Have the students also answer the following questions:

1. When you are enjoying summer in Philadelphia, what do you think children are doing in Argentina? Why? (Hint: Look on a map, and think about where Argentina is located. An illustration of the earth and the sun may help you explain your answer.)

1. What kind of weather would you expect to experience if you lived in Ecuador? Why? (Hint: Look at a map to see where Ecuador is?)
2. If you are going to visit your friend in Chile over your winter vacation, what kind of clothes would you pack? Why?
3. What's your favorite season? Why do you like this season?

Point out to the students that they may have already noticed the fact that the days get shorter in the winter and longer in the summer. For example, they may have realized that they can play outside much later in the summer because the sun sets later. On the other hand, in December and January, the sun sets around 5 PM.

Think about why we change our clocks back in autumn and forward in spring?

For a fun activity dealing with autumn, see "Fall Colors".

SCIENCE CONTENT STANDARD #2: PHYSICAL SETTING:

This activity helps to satisfy Benchmark 1 for grades 5-8: "Understand and illustrate the effects of the solar system on the earth's day and year." It also satisfies Benchmark 6 for grades K-4 which states that students should "understand that the earth is one of several planets that orbit the sun".

SCIENCE CONTENT STANDARD #6: BRIDGES TO THE MATHEMATICAL AND TECHNOLOGICAL WORLD:

Since this activity involves reading the newspaper or looking on the internet to collect data and graphing this data, Benchmark 1 for grades 5-8 is satisfied: "understand that multimedia communication devices as well as writing, drawing, and measuring using correct units are ways to communicate information to others". For the same reasons, Benchmark 3 is satisfied: "understand that technology and mathematics are essential to science for access to outer space and other remote locations, for sample collection and treatment, for measurement, data collection and storage, and for computation and communication of information".

Clearly this lesson fits well into a unit on space or seasons. Moreover, it incorporates skills pertinent to many other subject areas. Finding and understanding information in the newspaper or on the internet are very useful skills. This lesson also ties in with social studies since the students are asked to think about other areas of the world. Finally, it incorporates graphing skills, writing skills, and map skills.