Mondo Knows Facts
Light travels at nearly three hundred million metres per second
In a vacuum light travels at an exact speed of 299,792,458 metres per second
Photons travel through empty space at a constant maximum speed that serves as the universal speed limit in physics. Nothing with mass can accelerate to this speed because doing so would require an infinite amount of energy. The metre itself is defined based on this constant velocity.
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Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.
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Tags: physics, light, speed of light
Light travels at nearly three hundred million metres per second: the short answers
- Where does this come from, and can I check it?
- In a vacuum light travels at an exact speed of 299,792,458 metres per second. The figure is taken from NIST, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
- Is this really a science fact?
- Yes. It sits on the Science shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
- What else can I read about it?
- The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.