Finding the Speed of Light: The 1676 Discovery that Dazzled the World

By: Mark Weston

Illustrator: Rebecca Evans

More than two centuries before Einstein, using a crude telescope and a mechanical timepiece, Danish astronomer Ole Romer measured the speed of light with astounding accuracy. How was he able to do this when most scientists didn’t even believe that light traveled? Like many paradigm-shattering discoveries, Romer’s was accidental. Night after night he was timing the disappearance and reappearance of Jupiter’s moon Io behind the huge, distant planet. Eventually he realized that the discrepancies in his measurements could have only one explanation: Light had a speed, and it took longer to reach Earth when Earth was farther from Jupiter. All he needed then to calculate light’s speed was some fancy geometry.

Afterword. Further information about Ole Romer. Time line. Full-color illustrations.

ISBN: 9780884485452

JLG Release: Sep 2019

Sensitive Areas: None
Topics: Ole Romer (1644–1710) , Light , Astronomy , Telescopes , Planets , Earth , Jupiter , Geometry , Science and technology

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Book Details



First Release

September 2019



Dewey Classification


Trim Size

9 1/3" x 11 1/3"

Page Count


Accelerated Reader

Level 5.1; Points: 1;

Scholastic Reading Counts

Level 5.6; Points: 3;


Level 860L


Print Book


Hardcover edition


Tilbury House

Potentially Sensitive Areas



Ole Romer (1644–1710), Light, Astronomy, Telescopes, Planets, Earth, Jupiter, Geometry, Science and technology,

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