Empirical Earth · The Sky — Sun, Moon & Stars

Libration — the Moon rocks, and we see 59%

The claim

“We see one fixed face — a disc that never turns.”

What is measured

We see about 59% of the Moon’s surface over time as it rocks ~±8°/±7° ( libration ). A fixed flat disc could never show more than one face.

What would show this is wrong

the identical lunar hemisphere always presented with no rocking, revealing 50% or less of the surface over time.

Sources

  1. Lunar libration. The Moon appears to rock ~±8° in longitude and ~±7° in latitude, so ~59% of its surface is seen from Earth over time. libration . link
  2. Lunar libration — amplitudes and what it reveals. Longitude libration reaches ±7.9° (eccentric orbit, period 27.55 d) and latitude libration ±6.68° (the Moon’s 6.68° tilt, period 27.21 d); w link
  3. Diurnal libration. Because we observe the Moon from Earth’s rotating surface rather than its center, our viewpoint shifts by up to a full Earth-diameter between moonrise and moonset, letting link
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