Phases, tides and eclipses
Half of the Moon is always lit by the Sun. What changes over a month is how much of that lit half faces us.
New moon
Sunlit side faces away
Waxing crescent
A thin arc after sunset
First quarter
Right half lit, high at dusk
Waxing gibbous
Most of the disc, growing
Full moon
Opposite the Sun, up all night
Waning gibbous
Rises later each evening
Last quarter
Left half lit, seen at dawn
Waning crescent
A sliver before sunrise
One face toward Earth
The Moon is tidally locked: it turns once on its axis in the same time it takes to orbit Earth, so the same hemisphere always faces us. A slight wobble called libration lets observers see about 59% of the surface over time.
Tides
The Moon's gravity pulls the oceans into two bulges, one facing the Moon and one on the opposite side, so most coasts see two high tides a day. Friction from the tides slowly lengthens Earth's day and pushes the Moon about 3.8 cm farther away each year.
Eclipses
A lunar eclipse happens at full moon when the Moon passes through Earth's shadow and turns a coppery red. A solar eclipse happens at new moon when the Moon passes between Earth and the Sun. Because the Moon's orbit is tilted by about 5 degrees, eclipses do not happen every month.