Empirical Earth · The Sky — Sun, Moon & Stars

The selenelion — Sun and eclipsed Moon at once

The claim

“You can see the Sun and a fully eclipsed Moon at the same time — impossible on a globe.”

What is measured

During a total lunar eclipse the Sun and Moon are 180° apart, yet horizon refraction lifts each ~0.5–0.6°, more than its own radius, so both can clear opposite horizons for a few minutes. The effect is expected on a refracting sphere, not a refutation of one. More on refraction and the curve.

What would show this is wrong

a selenelion lasting hours, or seen far from sunrise/sunset, which atmospheric refraction could not account for.

Sources

  1. Selenelion & horizon refraction. During every total lunar eclipse, atmospheric refraction lifts the apparent Sun and Moon ~0.5–0.6° above their true positions, letting both briefly clear opp link
  2. A documented selenelion. Selenelions have been recorded since antiquity (the Royal Greenwich Observatory logged events in 1590, 1648, 1666 and 1668); the total lunar eclipse of 8 October 201 link
  3. Refraction at the horizon. Standard atmospheric refraction lifts a celestial body by about 34–35 arc-minutes at the horizon — slightly more than the Sun’s ~32-arc-minute width — so sunrise a link
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