Light, Shadows, and Seasons

Students measure shadows weekly to chart if the shadow gets larger or smaller


Date Long-Term Project Schedule
Sept Practice measuring classroom objects using cm or inches
Present intro lesson on year-long project
Choose consistent time of day for taking measurements throughout the year
Take the first reading with students
Oct Take readings every other week at the same time of day on sunny days and transfer info to data sheets
Nov Adjust time for Daylight Savings Time on November 5th
Take two readings per month. Each student plots data on the data sheets
Dec Take one reading (unless you can get 2 in)
Plot all the data students have collected up until now on a graph (can be done in January)
Jan RTake readings every other week at the same time of day on sunny days and transfer info to data sheets
Feb Take readings every other week at the same time of day on sunny days and transfer info to data sheets

OBJECTIVES:
  1. Natural light is produced by stars including our Sun.
  2. Light moves and if something gets in the way it produces a shadow.
  3. Understand that day and night are caused by the Earth's rotation.
  4. Understand that seasons are caused by the Earth's tilt on its axis as it revolves around the Sun during the year.
  5. Students act as scientists by measuring shadows, recording the data, plotting the data and then interpreting why the shadows change its length.
VOCABULARY:
MATERIALS:

BACKGROUND:

This long-term project helps students understand about the properties of light and what causes shadows. In their larger study of light, they will learn what causes day and night as well as what causes the seasons—why days get longer and shorter.

A shadow is an area where light from a light source is obstructed by an object. The shadow occupies all of the space behind an opaque object with light in front of it.

A year is the time it takes for the Earth to orbit the Sun once. As it orbits, the Earth has a tilt on its axis relative to the Sun, causing different seasons. Also, the tilt of the Earth's axis causes the angle of the sun (its apparent height in the sky) to differ during the year. This angle difference causes a change in the length of shadows. Low angles create longer shadows and high angles produce shorter shadows.

For the northern hemisphere, summer is when the northern hemisphere is tilted toward the Sun and winter is when it is tilted away from the sun. The days are longer and the shadows are shorter in summer. Conversely, the days are shorter and the shadows are longer in winter.

PROCEDURES:

  1. The teacher needs to find a place on the playground that can be sunny at the time the class will take the reading. (Note: Due to shadows from trees and buildings, an ideal place at 10am may not be an ideal place at 1pm. Be sure to check the shadows at the time students will be taking measurements. Remember to adjust for Daylight Savings time in November and March).
  2. Each student will measure shadows and record shadow length on a shadow card. The cards are marked with the cardinal directions and a center point where the shadow stick will be set.
    3. If it is rainy or overcast, delay the reading until the next sunny day that works. It is important that the cards are aligned similarly for each reading with the north symbol (N) pointed as close to north as possible. This will allow students to practice cardinal directions and to notice that the sun appears to move from east to west during the day. Painted lines on the playground are ideal so multiple students can align their cards to the same orientation. After orienting their cards, students use their pencils to mark the end of the shadow on the card. They will write the date next to the mark.
  3. In the classroom, students should use a ruler to draw a line from the center point of the shadow graph and then measure the line and record the length on the card. Students transfer the date and length data from their shadow cards to their Data Sheet Summary.
  4. Measurements should be taken bimonthly where possible. Teachers will decide whether measurements will be taken in centimeters or inches (we recommend centimeters).
  5. At the end of the project, information from the Data Sheet Summaries will be used to make a line or bar graph for the year showing the changes in shadow length from month to month.
  6. Ask students what patterns they see in the graph. Which months had longer shadows? Which months had shorter ones? Review why shadow length changes throughout the year in terms of the earth’s tilt relative to the Sun.