Seven questions
about the Moon

The questions everyone has, answered clearly — each one an interactive lesson in the Moon Explorer app.

• Why does the Moon have phases?
  Half the Moon is always lit by the Sun. The phases are just our changing view of that lit half as the Moon orbits Earth every 29.5 days — not Earth’s shadow.
• Why doesn't the Moon fall down?
  It is falling — continuously, toward Earth. But it also moves sideways at about 1 km/s, so it keeps missing. That endless falling-and-missing is what an orbit is.
• How far away is the Moon?
  On average 384,400 km — but the orbit is elliptical, so it ranges from about 356,000 to 406,000 km. We know the distance to within millimetres by bouncing lasers off reflectors left by Apollo.
• Why do we only ever see one side of the Moon?
  The Moon rotates — but exactly once per orbit, so the same face always points at Earth. This tidal locking is no coincidence: Earth’s gravity braked the Moon’s spin billions of years ago.
• Why does the Moon look upside down in the southern hemisphere?
  Observers in Australia and observers in Europe stand “head-to-head” on a sphere, so they see the same Moon rotated 180°. Neither view is the right way up.
• How does the Moon cause tides?
  The Moon’s gravity pulls hardest on the ocean nearest it and weakest on the far side, stretching Earth’s water into two bulges. Earth rotates through both — two high tides a day.
• How do eclipses happen?
  Eclipses are alignments: a solar eclipse is the Moon’s shadow touching Earth at new moon; a lunar eclipse is Earth’s shadow covering the Moon at full moon. The Moon’s tilted orbit is why they don’t happen monthly.

Dates and times are in Universal Time (UT). The free Moon Explorer app for Android converts everything to your local time and your exact location — fully offline, with no ads or accounts.