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Small Moon, Big Sun 3

This is a 4-H Solar Eclipse activity by Cynthia Canan, PhD, State 4-H STEM Specialist, Ohio State University Extension and Sara Newsome, 4-H Alumnus and STEM Student Assistant, The Ohio State University
Reviewed by: Wayne Schlingman, PhD, Director of the Arne Slettebak Planetarium,  The Ohio State University, Jessica George, Program Assistant, 4-H Youth Development,  Ohio State University Extension-Erie County and Travis West, Extension Educator,  4-H Youth Development, Ohio State University Extension-Vinton County

Topic: Space Science | Estimated time: 30 minutes | For pairs and groups (INTERMEDIATE to ADVANCED level) | PDF for PRINTING

The moon covers the sun during an eclipse.A total solar eclipse is a rare and awe-inspiring astronomical event that occurs when the moon completely covers the sun, temporarily blocking out its light. As total darkness consumes the path of totality, the temperature could drop, stars and planets could become visible, and animals could behave as if it were nighttime. But we know the moon is smaller than the sun, so how does the moon cover the sun?

Materials

  • coin (one, such as a penny, nickel, dime, or quarter)

  • measuring tape

  • masking tape

  • paper plates (various sizes, any color)

  • tables 1–6 (one copy each)

Be sure to complete this activity in a long space, such as a hallway or gym.

What To Do

  1. Tape any paper plate to a wall at eye level.
  2. Stand in front of the plate while holding the coin in your hand at eye level. Stretch your arm straight out in front of you and hold the coin against the plate.
  3. Close one eye and look at the coin with the plate in the background. Begin taking steps backward while holding the coin straight out. Stop when the coin appears to be the same size as the paper plate (covers the entire plate when you line up the coin and plate).
  4. Using masking tape, mark the ground where the backs of your feet have stopped.
  5. Measure the distance (length) in inches from the masking tape to the plate (Lp) and write it in the first row of a copy of Table 1. Always be sure to label the unit of measure.
  6. While holding the coin straight out, measure the distance in inches from your shoulder to your fingertips (Lc).
    Write this distance (length) in the second row of Table 1.
  7. Calculate the ratio of the distance between the plate (Lp) and the coin (Lc) from your eyesight by dividing the two measurements (Lp ÷ Lc). Round your results to the nearest one (whole number). Record your result in Table 1.

This result tells you how much farther the plate is from your eyes compared to the coin. If the quotient (answer) is 6.25, then the plate is 6.25 times farther from your eyes than the coin. See Example 1.

Example 1 shows a chlld holding a coin in front of a plate on the wall, with the following measurements in a chart: Length to plate (Lp) 75 inches; Length to coin (Lc) 12 inches; and Plate/coin length ratio rounded to nearest one (Lp ÷ Lc) 6.

  1. Measure the diameter of the paper plate (Dp) in inches and write it in the first row of Table 2.
  2. Measure the diameter of the coin (Dc) in inches and write it in the second row of Table 2.
  3. Calculate the ratio of the diameter between the plate (Dp) and the coin (Dc) by dividing the two numbers (Dp ÷ Dc). Round your results to the ones place. Record your results in Table 2. This tells you how much bigger the plate is compared to the coin.

For example, if the quotient (answer) rounded to the nearest one is six, then you can say that the plate is six times bigger than the coin. See Example 2.

Example two shows the diameter, or length across, a plate (Dp) is 6 inches; the diameter, or length across, a coin (Dc) is .955 inches; and the plate/coin diameter ration rounded to the nearest one (Dp ÷ Dc) is 6.

Table 1 Is a 3-column chart with rows for Length to plate (Lp); Length to coin (Lc); and Plate/coin length ratio (distance ration) rounded to the nearest one (Lp ÷ Lc). Table 2 Is a 3-column chart with rows for Diameter of plate (Dp); Diameter of coin (Lc); and Plate/coin diameter ratio rounded to the nearest one (Lp ÷ Lc).

  1. Compare your distance and diameter ratios, what do you notice?
  2. Repeat the experiment using a plate of a different size. Record your results in Table 3 and Table 4.

Table 3 Is a 3-column chart with rows for Length to plate (Lp); Length to coin (Lc); and Plate/coin length ratio (distance ration) rounded to the nearest one (Lp ÷ Lc). Table 4 Is a 3-column chart with rows for Diameter of plate (Dp); Diameter of coin (Lc); and Plate/coin diameter ratio rounded to the nearest one (Lp ÷ Lc).

  1. Compare the resulting distance and diameter ratio.
  2. Repeat the experiment using a plate of another different size. Record your results in Table 5 and Table 6.

Table 5 Is a 3-column chart with rows for Length to plate (Lp); Length to coin (Lc); and Plate/coin length ratio (distance ration) rounded to the nearest one (Lp ÷ Lc). Table 6 Is a 3-column chart with rows for Diameter of plate (Dp); Diameter of coin (Lc); and Plate/coin diameter ratio rounded to the nearest one (Lp ÷ Lc).

  1. Compare the resulting distance and diameter ratio.

Talking It Over

Write your answers to these questions and talk about them with your project helper or another caring adult. 

SHARE What happens during a solar eclipse?

REFLECT How does the distance of the sun and moon impact an eclipse?

GENERALIZE Why is the sun’s distance from Earth important to us?

APPLY Why is it important to know the distances between planets and stars?

More Challenges

Build a model to represent the size and distance differences among the sun, moon, and Earth!

The sun, moon, and earth during a total eclipse.

Background

We know the moon is much smaller than the sun. In fact, the moon is about 400 times smaller than the sun. This means that if the sun were the size of a basketball, the moon would be about the size of a
pinprick or a single dot made by a sharp pencil. How can such a small moon cover the big sun? The answer is in the distance between Earth and the sun and Earth and the moon.

When we look at an everyday item and hold it closer to our eyes, it will appear bigger compared to when the same item is held farther away from our eyes. The same phenomenon occurs when we observe objects in the sky from Earth: an object closer to Earth will appear bigger compared to the same object when it is farther away from Earth.

Even though the moon is 400 times smaller than the sun, it is also about 400 times closer to Earth compared to the sun. Because of these similar ratios in distance and size, the moon and the sun actually
appear to be similar in size when we observe the sky from Earth. This is why, when the moon moves in front of the sun, the moon can cover the sun completely.

Did you know?The moon moves to cover the sun during an eclipse.

The moon is slowly pulling away from Earth, which means the time will eventually come when the size ratio of the moon and sun will no longer match their distance ratio. Sometime in the future, the moon will appear too small to create a total solar eclipse.

Vocabulary

astronomical. Relating to the study of objects outside earth’s atmosphere.

path of totality. The path of the moon’s shadow across Earth’s surface.

phenomenon. An observable fact or event of scientific interest

ratio. A number that shows the relationship between two amounts.

Learn more!

Watch Greek Physics: Calculating the distance to the Sun and Moon and learn how Aristarchus determined the distance to the sun and moon based on several observations. youtube.com/watch?v=urgYWNCN-RA


SOURCES

“How Is the Sun Completely Blocked in an Eclipse?” NASA Science Space Place. spaceplace.nasa.gov/total-solar-eclipse/en
“Eclipse: How can the little Moon hide the giant Sun?” NASA Sun-Earth Day. sunearthday.nasa.gov/2007/materials/eclipse_smallmoon_bigsun.pdf

Unless otherwise noted, all images provided by iStockphoto.com by Getty Images.

LEARNING OUTCOMES

Project skill: Understanding the spatial relationships of the Earth, sun, and moon during a solar eclipse event | Life skill: Problem solving | Educational Standard: NGSS MS-ESS1-1. Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons. | Success indicator: Makes an analog model of a solar eclipse event

For more solar eclipse activities, visit go.osu.edu/4hsolareclipse.