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Scale of Things: The Earth and Moon


Last week we began a discussion about the scale of things by talking about how big the Earth is and our size on the Earth.  Today, let’s talk about the Earth and Moon.  The Moon, our companion in space, has a diameter of about 2,100 miles, which means it is about one-fourth the size of the Earth.  Now while the Moon is smaller than the Earth, that is actually big compared to other moons in the Solar System relative to the planets they orbit.  Most of the moons in the Solar System are only about one-hundredth the size of their planet.  Our Moon is so big that it actually stabilizes the rotation of the Earth.  The distance between the Earth and the Moon is about 240,000 miles; this is about 30 Earth diameters.

So to try to visualize the Earth-Moon system on a proper scale for both size and distance, take two regular piece of papers and tape them together length-wise so you have one really long piece of paper.  Near the left hand side, draw a circle one-half of an inch in diameter.  This will be our Earth.  Now from the center of this circle, measure to the right 15 inches (which is 30 Earth diameters on this scale).  At that spot draw a tiny circle with a diameter of one-eighth of an inch; that is our Moon!  Take a look at what you have; that is the Earth-Moon system at a proper scale.  If you go to a computer and ask to see a picture of the Earth-Moon system, see how few are actually depicted at a proper scale. 

Next week we’ll discuss the size and scale of our Solar System!


Follow your curiosity to the Fred G. Dale Planetarium at Wayne State College.

Dr. Todd Young hails from Minnesota and received his undergraduate degree in Physics & English from the University of Minnesota – Morris, his Master’s degree in Physics from Purdue University, and his Ph.D. from the University of Nebraska – Lincoln in Astrophysics. He has worked at Wayne State College since receiving his doctorate in 1998 and is currently a full professor of physics and astronomy. He teaches a variety of courses at Wayne State College, including university physics, astronomy, general education science, and astrophysics.
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