Overview

In this activity, students use a paper plate to build a model that shows why lunar eclipses don’t happen during every full moon.

Materials

Paper plate, take-out container, or another flat surface with raised edges (thick material recommended), 1 per student or group

Pencil, pen, OR marking pen

Scissors

Small ball, approximately 3-5 centimeters (1-2 inches) in diameter, or another object to represent the Sun, 1 per student or group

(Optional) Jar, lid, or another round object that can be used to trace out a circle

Management

• Students who are unfamiliar with the phases of the Moon would benefit from first completing the Moon Phases lesson or the independent Make a Moon Phases Calendar and Calculator project.
• Cutting the disconnected half-circles in the middle of the plate can be tricky. Model cutting for students who need to see it done. Have some spare plates on hand in case students cut too much. Thicker plates will help eliminate tears in the paper at the pivot points mentioned in Step 8.
• For students with less-developed fine motor skills, consider pre-cutting the plates.

Tips for Remote Instruction

• Viewing the paper plate cutout can be difficult through a webcam, so consider using some of the images in this lesson page to display for students.
• Using a top-down view of the plate when marking the plate and moving it may eliminate confusion that can result if your camera is pointed toward the plate from a perspective that is different than the students’ view of their screen or their plate.

Background

Eclipses can occur when the Sun, Moon, and Earth align. Lunar eclipses can happen only during a full moon, when the Moon and Sun are on opposite sides of Earth. At that point, the Moon can move into the shadow cast by Earth, resulting in a lunar eclipse. However, during most full moons, the Moon’s slightly tilted orbit brings it above or below Earth’s shadow.

These side-by-side graphics show how the Moon, Sun, and Earth align during a lunar eclipse (left) versus a non-eclipse full moon (right). Credit: NASA Goddard Visualization Studio | + Expand image

The time period when the Moon, Earth and Sun are lined up and on the same plane – allowing for the Moon to pass through Earth’s shadow – is called an eclipse season. Eclipse seasons last about 34 days and occur just shy of every six months. When a full moon occurs during an eclipse season, the Moon travels through Earth’s shadow, creating a lunar eclipse.

When a full moon occurs during an eclipse season, the Moon travels through Earth's shadow, creating a lunar eclipse. Credit: NASA/JPL-Caltech | + Expand image

Unlike solar eclipses, which can only be viewed through special glasses or equipment for a few short minutes in a very limited area, a total lunar eclipse can be seen with the naked eye for up to an hour by anyone on the nighttime side of Earth – as long as skies are clear.

Procedures

1. Ask students what they know about the phases of the Moon, specifically about when the full moon and new moon phases occur. Clear up any misconceptions, and ask what students know about lunar eclipses. If necessary, explain that lunar eclipses occur during full moons when the Moon passes through Earth’s shadow. Tell students they are going to create a model that explains why lunar eclipses don’t occur during every full moon.
2. Have students draw or trace a circle 3-5 inches (8-13 centimeters) in diameter in the approximate middle of the plate.


Step 2. Image credit: NASA/JPL-Caltech | + Expand image

3. In the center of that circle, students should draw a small circle and label it "Earth."


Step 3. Image credit: NASA/JPL-Caltech | + Expand image

4. At the edge of the paper plate, students need to make a small arrow pointing outward that they will use as a reference in the next step and later in the lesson.


Step 4. Image credit: NASA/JPL-Caltech | + Expand image

5. On the inside edge of the larger circle, students will mark four evenly spaced points at the 0, 90, 180, and 270 degree marks, or for students who haven't learned degrees, at the 3, 12, 9, and 6 o’clock spots, respectively. Students should align the 90 degree (12 o’clock) point with the reference mark they made in Step 4.
6. Students should label each point as follows
   
   
   • Point 1 (at 90 degrees, or 12 o’clock)
   • Point 2 (at 180 degrees, or 9 o’clock)
   • Point 3 (at 270 degrees, or 6 o’clock)
   • Point 4 (at 0 degrees, or 3 o’clock)
   
   Guide students so that they all label their points in the same way.


Steps 5 and 6. Image credit: NASA/JPL-Caltech | + Expand image

7. Students will need to carefully cut along the larger circle they drew, as follows. Poking a starter hole with a pencil or other pointed object on the line will make starting the cut easier.
   
   They should stop cutting at the 180 and 0 degree marks, leaving a few millimeters of uncut space before continuing to cut around the circle. They should be left with a circle still connected to the plate at 180 and 0 degrees.


Step 7. Image credit: NASA/JPL-Caltech | + Expand image

8. With both cuts made, students will need to gently twist the cut circle in the center of the plate. It should pivot at 0 and 180 degrees marks so that the 90 degree point rises up slightly and the 270 degree point dips down slightly. Students should be careful not to tear the paper between the two cuts.


Step 8. Image credit: NASA/JPL-Caltech | + Expand image

9. Tell students that the edge of the tilted circle represents the tilted orbit of the Moon around Earth. Tell them the flat part of the plate represents the plane in which Earth’s shadow falls.
10. Have students align the reference arrow on their plate so it's pointing away from them. Then, have them place their object representing the Sun on the opposite side of the plate from the reference arrow.


Step 10. Image credit: NASA/JPL-Caltech | + Expand image

11. Ask students the following questions. They can use the optional student worksheet to record their answers:
    
    In this orientation…
    • Where would the full moon be located?
      Answer: Point 1
    • Is it in the same plane as Earth’s shadow?
      Answer: No
    • Would there be a lunar eclipse during this full moon?
      Answer: No
12. Have students move their plate counter-clockwise 90 degrees, or to the 9 o’clock position, relative to the Sun, while keeping their reference arrow pointed in the same direction. Tell them that as Earth orbits the Sun, the orientation of the Moon’s tilt stays the same. Ask them the questions as before:
    
    In this orientation…
    • Where would the full moon be located?
      Answer: Point 2
    • Is it in the same plane as Earth’s shadow?
      Answer: Yes
    • Would there be a lunar eclipse during this full moon?
      Answer: Yes


Step 12. Image credit: NASA/JPL-Caltech | + Expand image

13. Have students independently repeat these steps after moving the plate to the 6 o’clock and 3 o’clock positions relative to the Sun, and have them record their answers.

Discussion

• Ask students what they noticed about the pattern of eclipses.
• Tell students that the time when the Moon is in the same plane as Earth’s shadow is called an eclipse season. Ask them to predict approximately how often eclipse seasons occur based on their model.

Assessment

• Students should correctly answer the three questions for each position of their model.
• Students should be able to explain why lunar eclipses only occur during certain times of the year.

Extensions

• Ask students to make connections between when lunar eclipses occur and when solar eclipses might occur.

Explore More

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