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I encountered this statement that the dark side of the moon is hidden from our sights. Could someone please explain?


marked as duplicate by HDE 226868, Stan Liou, David Hammen, TildalWave, Wayfaring Stranger Sep 1 '15 at 20:57

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    $\begingroup$ The dark side of the Moon is not hidden from our sight. When the Moon is nearly new, you can see a thin band of the Moon that is well lit, but you can also see the rest of the Moon. That is the dark side of the Moon. People regularly confuse the dark side of the Moon with the far side of the Moon. Most of the latter is hidden from our sight. $\endgroup$ – David Hammen Aug 29 '15 at 18:41

Yes, the dark side of the moon is mostly hidden from earthbound observers. This is due to tidal locking:

A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner. This causes one hemisphere constantly to face the partner body.

In other words, one moon-year is just as long as one moon-day.

The left-hand side shows the actual configuration of earth and moon: The orbit is locked and we can only observe one side of the moon. On the (fictional) right-hand side, the moon does not rotate around itself and we can observe different areas of the moon at different times.

Left: Tidally locked orbit. Right: Orbit without any spin.

I should note that we can actually observe not 50%, but around 59% of the moon's surface because of libration and parallax effects that cause the moon to slightly "wobble": Simulated view of the moon, demonstrating librations.

You can find all those images and further explanation in the linked wikipedia articles on tidal locking and libration.

  • $\begingroup$ Read David Hammen's comment on the question, you are talking about the far side of the Moon not the Dark Side $\endgroup$ – Conrad Turner Aug 30 '15 at 13:13
  • $\begingroup$ Yes, the question and my answer are about the far side. However, this side is typically referred to as dark side even though it does get illuminated by the sun in periods of two weeks. I don't see what else the dark side could mean in this context. $\endgroup$ – Daniel Lenz Aug 30 '15 at 20:35
  • $\begingroup$ Erroneously refered to as the dark side, you could try pointing this out $\endgroup$ – Conrad Turner Aug 30 '15 at 22:03

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