Empirical Earth · The Sky — Sun, Moon & Stars

The round shadow — Aristotle's eclipse argument, still unbeaten

The claim

“A lunar eclipse is just the Moon dimming; it says nothing about Earth’s shape.”

What is measured

Earth’s shadow on the Moon is always a circular arc, in every eclipse at every angle, and only a sphere casts a round shadow from every direction (Aristotle, ~350 BCE).

What would show this is wrong

a single lunar eclipse showing a straight or angular shadow edge instead of a circular arc.

Sources

  1. Shape of Earth's shadow in lunar eclipses. During a lunar eclipse the Earth's shadow on the Moon is always a circular arc, implying Earth ~3.7× the Moon's diameter; only a sphere casts a rou link
  2. Why the eclipsed Moon turns red. NASA: during a total lunar eclipse the only sunlight reaching the Moon is filtered through a thick slice of Earth’s atmosphere, which scatters out the blue a link
  3. Sizing the Moon from the eclipse shadow. For a central lunar eclipse the diameter of Earth’s umbra at the Moon averages about 2.65 lunar diameters; by timing how long the eclipsed Moon takes link
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