Learning Activity on the Physical Scales:
The Earth-Moon System

Earth Layers
Earth geologic layers and orbital space. Credits: NASA


The basic structure of the Earth is divided into the three geologic layers of the core, mantle and crust, with the atmosphere surrounding them. These layers are very different in thickness. In fact, if you were to compare the distance from the center of the Earth to the top of the atmosphere with the 100 yards of a football field, the core and the mantle would cover 97.5 yards of the field, the crust would measure less than a yard and the atmosphere would be the final 1.5 yards. For the remainder of this learning activity, we will be describing physical scales using the metric system of units that is used by NASA and other scientists. Therefore, expressing our football field analogy in metric units, the football field would be 91.4 meters, the core and the mantle could cover 89.2 meters, the crust would measure less than a meter, with the atmosphere covering the final 1.4 meters.

Earth layers with the core in orange, the mantle in gray, the crust in brown, and the atmosphere in blue.

Most satellites are in Low Earth Orbit (LEO) a few hundred miles above the atmosphere. While this seems like a long way from Earth, if we compare it to the orbit of the moon which is around 750 times further away, it is actually pretty close. Take a closer look at the image below and compare the altitude of orbits to the size of the Earth's layers!

View of orbital altitudes
The basic geologic layers of the Earth. Credit: NASA. [Large Image]



Try this activity to visualize the difference between the orbit of a CYGNSS satellite to the orbit of the moon. You will need a gymnasium or field, a 30.5 cm diameter globe, a baseball to represent the Moon, scissors, string, a meter stick, and a calculator.

  1. Wrap the string around the equator of the globe once and cut off that piece. Measure the string's length to find the circumference of the globe and record your measurement.
  2. Determine the ratio of the altitude of the CYGNSS orbit to the Earth's circumference by dividing the altitude of the CYGNSS orbit (500 kilometers) by the Earth's circumference (40,000 kilometers). Record this value.
  3. Multiply your result from Step 2 by the number you recorded in Step 1. This is the approximate distance from the surface of the globe that the CYGNSS spacecraft would be orbiting (at this scale). Record your solution and cut a piece of string to this length.
  4. The average distance between the Earth and the moon is 382,500 km. Using this information, calculate the distance that the baseball (moon) should be from the globe in order to have the same spatial scale as the true Earth-moon system. You should use the same approach as you used in Steps 2 and 3. Record your solution and then measure out a piece of string of this length and tie it to the baseball. Compare this length to the length in Step 3.
  5. With the globe at the center and one student on each end of the long string, try walking around the globe to simulate the moon's orbit.

Next Generation Science Standards

The following Next Generation Science Standards will be taught through this lesson:

MS-ESS1-3. Analyze and interpret data to determine scale properties of objects in the solar system.

Clarification Statement: Emphasis is on the analysis of data from Earth-based instruments, space-based telescopes, and spacecraft to determine similarities and differences among solar system objects. Examples of scale properties include the sizes of an object’s layers (such as crust and atmosphere), surface features (such as volcanoes), and orbital radius. Examples of data include statistical information, drawings and photographs, and models.


Try these additional NASA educational activities to learn more about Earth-Space scales, satellites, the CYGNSS mission and the NASA Pathfinder program, of which CYGNSS is a part.

  1. CYGNSS Mission Homepage The official NASA web page for the CYGNSS mission, this web-page contains stories and media content related to the mission.
  2. NASA Pathfinder Program Homepage The CYGNSS mission is part of the Earth System Science Pathfinder (ESSP) Program, a science-driven Program designed to provide an innovative approach to Earth Science research by providing periodic, competitively selected opportunities to accommodate new and emergent scientific priorities.
  3. How High Is Space? This is a lesson about the location of common Earth objects within layers of our atmosphere. Learners will construct a scale model of the atmosphere in order understand where the common objects, such as clouds, airplanes, and space shuttles can be found within its various layers.
  4. What Is A Satellite? A satellite is a moon, planet or machine that orbits a planet or star. For example, the Earth is a satellite because it orbits the sun. To learn more about satellites, check out this cool NASA web-page