SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/astro-kepler-first-law

Where is the Sun in a planet's elliptical orbit?

At one focus of the ellipse, not at its center.

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  1. At one focus ✔
  2. At the exact center
  3. At perihelion

Why: Kepler's first law says planetary orbits are ellipses with the Sun at one focus. The planet-Sun distance therefore changes throughout an orbit.

Huh, didn't know that: A circle is the special ellipse whose eccentricity is zero and whose two foci coincide.

The dad joke
Kepler kept his work focused, specifically on one focus.
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References

Answer: At one focus. Kepler's first law says planetary orbits are ellipses with the Sun at one focus. The planet-Sun distance therefore changes throughout an orbit.

  1. Orbits and Kepler's Laws science.nasa.gov/solar-system/orbits-and-keplers-laws
    Each planet's orbit about the Sun is an ellipse.
    Checked 2026-10-10.

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