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The Conversation
The Conversation
Jarred Roberts, Project Scientist, University of California, San Diego

Do photons wear out? An astrophysicist explains light’s ability to travel vast cosmic distances without losing energy

Light, whether from a star or your flashlight, travels at 186,000 miles per second. Artur Debat/Moment via Getty Images

My telescope, set up for astrophotography in my light-polluted San Diego backyard, was pointed at a galaxy unfathomably far from Earth. My wife, Cristina, walked up just as the first space photo streamed to my tablet. It sparkled on the screen in front of us.

“That’s the Pinwheel galaxy,” I said. The name is derived from its shape – albeit this pinwheel contains about a trillion stars.

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