Unit 1: Science Connection

How Far Away is the Moon?

Tom Murphy knows that the distance from Earth to the moon varies between 220,000 to 252,000 miles, depending on which day it is.

But that's not good enough for Murphy, a scientist at the University of Washington. He and some scientists want to know how far away the moon is from Earth in millimeters.

Murphy plans to spend the next several years bouncing laser light off small instruments left on the moon's surface by American astronauts during the Apollo moon missions of the 1960s and 1970s.

By calculating how long it takes the laser light to return to Earth, Murphy believes he can calculate the distance to the moon down to the last millimeter, roughly the width of a paper clip, if you can imagine that.

“We're not interested in distance itself,” Murphy said. “It's just a boring, arbitrary number.”

If Murphy doesn't care how far the moon is from Earth, why is he conducting this unusual space experiment?

Murphy hopes to unlock the mysteries of gravity, the force of attraction between two objects. Gravity keeps the planets revolving around the sun. Gravity also keeps our feet, cars, dogs, and houses on the ground.

Only by measuring how celestial bodies, such as Earth and its moon, interact can scientists begin to understand how gravity works, Murphy said.

Murphy's experiment may help solve all sorts of questions, such as whether gravity weakens as the universe expands.

“[With an experiment] like this, you never know what [you will find],” Murphy said.

vary:
To be different: The temperature varies from day to day.

arbitrary:
Based on or likely to rely on ones own wishes, opinions, or feelings than on reason, rule, or law.

interact:
To act on or affect each other: The children in the play group didn't interact well.

expand:
To make or become larger in size, volume, or amount.

Back to Article

Activity

Make a word web. Choose one of the words above, and write that word in the center of a piece of paper. Write down all of the words that you associate with the center word, and connect each one to the center word with a line. You may use a dictionary or thesaurus to help you. Be sure to include different forms of the word in your word web.

How Far Away Is the Moon? Quiz
Imagine that you have been asked to help the scientists at the University of Washington. You need to estimate the distance from the Earth to the moon in millimeters. Work with a partner to find out.