speed of light Archives

What Is the Speed of Light? The Number That Defines the Meter

October 20, 2026October 18, 2026 by Marcus Webb

What is the speed of light? In vacuum it is exactly 299,792,458 meters per second, or about 186,282 miles per second. Since 1983 that number has not been a measurement. It is a definition, and the meter is the thing being defined by it. That reversal is the strangest part of the story. For three … Read more

What Is a Light-Year? (It’s Not Time, and That’s the Point)

October 18, 2026 by Marcus Webb

Ask someone what a light-year is and you’ll usually get “a really long time.” It isn’t. What is a light-year is one of the most common mix-ups in all of science: the word “year” is sitting right there in the name, doing nothing but confusing you. A light-year is a distance. Specifically, it’s how far … Read more

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