Children reinforce their understanding of seasonal dynamics by reading and graphing annual day-length data to determine the relative north or south latitude, and name, of their “mystery city.”

The children should have a basic understanding of why Earth experiences seasons. Information can be found in “About Seasons” and an activity to reinforce the causes of Earth's seasons can be found at Season Sequences.

Clarify any misconceptions about hours of daylight being the only cause of seasons. Relative seasonal temperatures are caused by Earth's axial inclination and angle of incoming sunlight, as well as by day length (how many hours our Sun is above the horizon and how long it spends at its highest elevation).

Find out what the children know about changing daylight hours through the year. Gather their ideas — correct and incorrect — to revisit at the close of the activity.

• Ask the children how daylight hours change through the year. (“Longer days” in the summer and fewer hours of daylight in the winter)
• Do the number of daylight hours change the same way throughout the year everywhere on our Earth?
• When is it summer at the north pole? (July)
• South pole? (January)
• What is day length like in the summer at the north pole? (24 hours of light)

Invite the children to explore daylight duration in different cities across our Earth during the year.

• Do they have any predictions for day length trends? Note their predictions.

Divide students into groups of 3 or 4. Provide each group with a copy of the Daylight Hours Across the Globe table, graph paper, and colored pencils. Assign each group a different letter (city) to plot. The groups are going to compare their data for the different locations.

Have the groups plot the number of daylight hours in their city for each month of the year on their graph.

• How might they best illustrate the changes throughout the year? (Graph the number of hours)
• What should they consider when making their graphs to compare? (Scales and axes should be the same; work with the groups to determine the appropriate scale)
• What should each graph have? (Labels on axes, title)

After completing their graph, groups should be able to determine at what times of year particular seasons occur in the city they plotted.

• Which seasons have more daylight hours? (spring and summer)
• Fewer daylight hours? (fall and winter)
• How does this compare with the time of year the seasons occur where they live? (Seasons in their hometown may provide clues to the approximate location of their unknown city)
• Which groups have cities in the northern hemisphere? (groups A, C, E, F, and H)
• The southern hemisphere? (groups B, D, G, and I)
• How do they know? (Northern hemisphere summer months — such as July — have more hours of daylight; southern hemisphere summers also have more hours of daylight, but occur “opposite” the northern hemisphere summer. Some cities just north or south of the Equator will only vary slightly from one another, and slightly throughout the year in their number of daylight hours)

Ask the groups to post their graphs and discuss the patterns they observe.

Invite the students to use the model of Earth's seasons to illustrate the distribution and duration of light for their city.

• What trends or patterns do they observe as they look at all the graphs?
• Based on their model of what causes Earth's seasons, what can they conclude about the placement of the cities? (those cities without extreme differences in day length are located near the equator, whereas locations at the poles do experience extreme differences in day length. Cities north or south of the equator experience longer days in summer and shorter days in winter)
• Are there times when all the cities experience approximately the same number of daylight hours? (Spring and fall)
• Why? (because during spring and fall, the Earth is tilted neither toward nor away from the Sun)
• Which cities are in the northern hemisphere? (Miami, Nairobi, Nome, Singapore, and Seattle)
• The southern? (Brisbane, Punta Arenas, Cape Town, and Vostok)
• Which are closer to the equator? (Those with smaller differences between the summer and winter day lengths i.e. Nairobi and Singapore)
• Which are closer to the polar regions? (Those with more extreme differences in summer and winter day length, i.e. Nome and Vostok)

If the children are unclear about any of these concepts, revisit a model of Earth's seasons to illustrate the differences between the timing of northern and southern hemisphere seasons, and the duration of summers versus winters in the polar regions compared to the equator.

Tape the index cards with the city names onto a wall in random order. Invite the groups to place their graph by the name of the city they think their graph represents. Have them refer to the globe and use the patterns of daylight hours they discussed to try to discover which city is theirs. They may alter their conclusions as they get more information and compare to other teams.

After all graphs have been correlated with a city, have the children place the graphs in order from the northernmost city to the southernmost city.

• Do the patterns of day length follow the children's previous observations about which graphs were from cities closer to the equator, which were closer to the south pole, etc.?

Extensions

Provide the children with names of other cities and ask them to predict what the graph would look like for those cities relative to their graphs.

• When does winter occur?
• Summer?
• Is there a significant amount of difference between winter and summer?

Key: Daylight Hours Across the Globe
Time is indicated as number of hours (h) and number of minutes (m)

Daylight Hours Across the Globe
Time is indicated as number of hours (h) and number of minutes (m)

More Activities

Last updated
January 4, 2007

Who?
Ages 13–16

How Long?
60–90 minutes

What's Needed?

• Graph paper
• Colored pencils or markers
• Globe
• Annual data tables of daylight hours for unidentified cities
• Tape

Connections to the National Science Standard(s):

Standards A&G (grades 9–12): Identify questions about seasonal changes using their own observations. Using logic and mathematical data, formulate an explanation about, and conceptual understanding of, how latitude affects seasonal variations. Critique and communicate explanations.