Where does this come from, and can I check it?

Planetary orbits are ellipses with the Sun at one focus, not perfect circles. The figure is taken from NASA, 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 2,600 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.

Mondo Knows Facts

Kepler replaced circles with ellipses

Planetary orbits are ellipses with the Sun at one focus, not perfect circles Using Tycho Brahe's careful observations of Mars, Johannes Kepler found that no circular orbit fitted the data. In 1609 he published the first two of his laws, describing elliptical paths and equal areas swept in equal times. The third law, relating orbital period to distance, followed a decade later. It sits in Mondo's science collection, one of 200 facts that each trace back to the reference below.

Where this comes from

NASA

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, astronomy, history

Kepler replaced circles with ellipses: the short answers

Where does this come from, and can I check it?: Planetary orbits are ellipses with the Sun at one focus, not perfect circles. The figure is taken from NASA, 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 2,600 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.