Astronomy 101: Astronomical distances

In this episode, learn how astronomers make sense of the enormous expanses in our universe.

By Bill Andrews

Astronaut Bruce McCandless shows how miniscule we are, even just compared to our planet.

Photo by NASA/STS-41B

“Space is big,” wrote Douglas Adams, and he wasn’t kidding. Familiar units of distance, like miles and kilometers, quickly become too unwieldy to use in cosmic discussions. After all, we don’t say the Empire State Building stretches 17,448 inches or describe a bacterium as measuring 0.000001 meter. Instead of ending up with similar “astronomical” figures, scientists use units like light-years, parsecs, and astronomical units to help make sense of it all.

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	Sun	Sun	Moon
RISE	—		—	PHASE	—
SET	—		—	DISK	—

	Mercury	Mercury	Venus	Venus
RISE	—		—
SET	—		—
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	Mars	Mars	Jupiter	Jupiter	Saturn	Saturn
RISE	—		—		—
SET	—		—		—
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