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SESK: Stuff Everyone Should Know · sesk.info/astro-jansky-first-radio

Karl Jansky discovered the first cosmic radio waves in the early 1930s. Where were they coming from?

The Milky Way Galaxy.

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  1. The Sun
  2. The Moon
  3. The Milky Way ✔

Why: Jansky, a Bell Labs engineer, noticed static that peaked about four minutes earlier each day. That matches Earth's spin relative to the stars, so the source was fixed among the stars: our galaxy.

Huh, didn't know that: The unit of radio flux used by astronomers, the jansky, is named after him.

The dad joke
Jansky was trying to fix static and found the galaxy instead. Best wrong number ever.
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References

Answer: The Milky Way. Jansky, a Bell Labs engineer, noticed static that peaked about four minutes earlier each day. That matches Earth's spin relative to the stars, so the source was fixed among the stars: our galaxy.

  1. OpenStax Astronomy 2e, 6.4 Radio Telescopes openstax.org/books/astronomy-2e/pages/6-4-radio-telescopes
    Subsequent investigation showed that the source of this radiation was part of the Milky Way Galaxy
    Checked 2026-10-10.

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