# Golf Ball Phases and Embroidery Hoop Eclipses

In the first half, students explore the dynamics of lunar phases to develop an understanding of the relative positions of our Moon, Earth, and Sun that cause the phases of the Moon as viewed from Earth.  Using a golf ball glowing under the ultraviolet light of a “blacklight” makes it easier to see the actual phase of the Moon.

In the second half, students adjust their orbits of their moons to gain a deeper understanding of eclipses.

The Activity

Step 1: Model the Moon’s motion first for the students.

Choose a student to hold the golf ball representing the Moon. The child's head will represent our Earth. Choose another student to stand with the blacklight representing the Sun. Turn out the room lights.  Before turning on the “Sun,” ask the students to observe the golf ball.

• Does the golf ball make its own light? (No)
• Does our Moon make its own light? (No)

Turn the light on and have the student with the golf ball hold it low in front of them, between the student and the light. Ask the student with the “Moon” to describe its appearance.

• What does he observe about the Moon? Is the part of the Moon we see from Earth illuminated? (No)
• What part is illuminated? (The part facing the “Sun” that they cannot observe from “Earth”)
• Based on this observation, does the Moon really have a “dark” side? (No)
• What phase of the “Moon” is he observing from “Earth”? (The new Moon)

Ask the student holding the “Moon” to slowly turn 90° while raising the golf ball to shoulder-height, keeping the Moon at arm's length.

• As the Moon revolves around the Earth, what happens to its appearance?  How does the illumination of the Moon change as viewed from the Earth? (It increases to 1st Quarter)

Ask the student holding the “Moon” to continue moving and raising the golf ball, until the ball is 180° away from the blacklight and just over the student’s head.

• What phase of the Moon is he observing when the Moon has orbited halfway around the Earth? (A full Moon)

Ask the student holding the “Moon” to slowly turn another 90° while lowering the golf ball to shoulder-height, keeping the Moon at arm's length.

• What phase of the Moon is he observing now, when the Moon has orbited three quarters of the way around the Earth? (3rd quarter, or last quarter Moon)

Step 2. Student Exploration

Once the students are comfortable with the motion of the Moon, starting low in front of the lamp and moving up to above their heads for full Moon, have each student take a golf ball and model the motions of the Moon, while the teacher holds the blacklight.

Have the students observe the changing illumination of the Moon, repeat the exercise so that each Moon phase is revealed. Start with the new Moon and have the students rotate in steps of 45degrees, pausing at each of the eight phases (waxing crescent, 1st quarter, waxing gibbous, full, waning gibbous, 3rd quarter, waning crescent) to invite the students to make observations about the illumination and to identify the phase.

Step 3.  Modeling Eclipses

After the students are comfortable with the motion of the Moon, remind them that the Moon’s orbit isn’t a perfect circle—it’s an ellipse.

• What are some objects that have elliptical shapes?

Show the students an embroidery hoop.  Hold the hoop at an angle to the blacklight that mimics the positions that the students have been moving their golf balls—low in the front and high in the back.  Ask the students about the effect this orbit has on the Moon’s appearance.

• Will the Moon block the Sun for people on Earth when it moves in this orbit?  Will the Earth block the sunlight from reaching the Moon in this orbit?  (no)

Explain that the Moon’s orbit remains tilted as the Earth orbits the Sun.  Walk with the embroidery hoop around the blacklight, stopping when you have moved one quarter of the way around the Sun.  Have a student demonstrate the motion of the Moon with a golf ball from this position for the class.

• Now when the Moon is low, what is its phase?  Where will it be at new Moon?  What will people on Earth see? (People on the right part of the Earth will see solar eclipse)
• Two weeks later, when the Moon is at full, what will people on Earth see? (A lunar eclipse, visible to everyone on the part of the Earth facing the Moon)

Continue moving the embroidery hoop around the blacklight, rotating the blacklight as needed.  Stop at another quarter of the way around the Sun.  Discuss the Moon’s appearance with the class.

• Will the Moon block the Sun for people on Earth when it moves in this orbit?  Will the Earth block the sunlight from reaching the Moon in this orbit? (no)

Continue moving the embroidery hoop around the blacklight, rotating the blacklight as needed.  Stop at the 3rd  quarter of the way around the Sun.  Discuss the Moon’s appearance with the class.

• Now when the Moon is low, what is its phase?  Where will it be at New Moon?  What will people on Earth see? (People on the right part of the Earth will see solar eclipse)

• Two weeks later, when the Moon is at full, what will people on Earth see? (A lunar eclipse, visible to everyone on the part of the Earth facing the Moon)
• How much time has past since we had the last solar eclipse and lunar eclipse?  (6 months)

Let the students practice moving their golf balls from these different locations, modeling both lunar and solar eclipses.  Ask them to demonstrate the position of the Moon during a solar eclipse, and then a lunar eclipse.

• What is the Moon’s phase for a solar eclipse?  (new)
• What is the Moon’s phase for a lunar eclipse? (full)

Conclude by letting them know that sometimes the Moon brushes through just part of the Earth’s shadow, resulting in a partial lunar eclipse, and sometimes the Moon only covers part of the Sun, resulting in a partial solar eclipse.  There are a total of 5 to 7 eclipses each year; some of these are partial eclipses, often a month apart.

Extensions
Several phases activities are available at http://www.lpi.usra.edu/education/skytellers/moon_phases/