Using the U.S. Naval Observatories Astronomical Observations Department, Data Services, Table of Sunrise/Sunset, Moonrise/Moonset, or Twilight Times for an Entire Year), download sunrise and sunset data tables for several locations at corresponding north and south latitudes (for example Moscow is approximately 55 degrees north; Cape Horn is approximately 55 degrees south latitude).
Select several cities, one per group, that represent a wide variety of latitudes. For each city, highlight the last day of each month. Divide the children into groups, with a different city data table for each group. Ask each group to calculate the number of hours between sunrise and sunset for their city for the last day of each month and to make a table showing this information.
Invite the children to graph the number of hours of daylight for the months of the year.
Because they will compare their results, the graph axes also should be comparable. Help the children decide on a standard graph, axes, and key and then have each group plot the 12 points (one for each month) for their city on their graph. As each group finishes with their graph, have them look on the globe to find the approximate latitude of their city. Have the groups post their graphs sequentially on a wall, with northern hemisphere cities above southern hemisphere cities of corresponding latitude. Invite the children to examine the plots.
Invite them to use their materials to model the interaction of our Sun and Earth to explain the changes. Lead a discussion of the causes of changing day length. An animated cartoon illustrating the movement of Earth around the Sun and the resulting change in day length can be found at this site. Day and Night Cycles offers a handson enhancement of this discussion.

Who? How Long? What's Needed?
Connections to the National Science Standard(s) Standards A& D(grades 5–8): Understand and communicate the scientific explanation of how objects in the solar system have regular and predictable motion, such as the apparent daily movement of the Sun in the day/night cycle and annually across seasons. Standard A (grades 9–12): Use tables and graphs to communicate results of investigation of Earth's day/night cycle. 