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SESK: Stuff Everyone Should Know · sesk.info/astro-au-light-minutes

How long does sunlight take to cross one astronomical unit, the average Earth to Sun distance?

About 8.3 minutes (about 499 seconds).

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  1. About 8.3 minutes ✔
  2. About 8.3 seconds
  3. About 1.3 seconds

Why: One AU is about 150 million km, and light covers 300,000 km each second, so the trip takes about 500 seconds. The Sun you see is the Sun of about 8 minutes ago.

Huh, didn't know that: 1 AU is defined as exactly 149,597,870,700 meters.

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The Sun is 8 minutes away, and still always on time for sunrise.
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References

Answer: About 8.3 minutes. One AU is about 150 million km, and light covers 300,000 km each second, so the trip takes about 500 seconds. The Sun you see is the Sun of about 8 minutes ago.

  1. OpenStax Astronomy 2e, 19.1 Fundamental Units of Distance openstax.org/books/astronomy-2e/pages/19-1-fundamental-units-of-distance
    The length of 1 AU can be expressed in light travel time as 499.004854 light-seconds, or about 8.3 light-minutes.
    Checked 2026-10-10.

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