The Moon does not emit its own light, shining instead by reflecting sunlight. Depending on the relative positions of the Earth, Sun and Moon, varying amounts of the lunar surface appear to be illuminated.
When the Moon
is at opposition
, i.e. on the opposite side of the Earth from the Sun
, the bright side of the Moon
is facing towards to the Earth, and we have a Full Moon
(position E in the diagram below).
The Full Moon
rises at sunset, transits the meridian
at midnight and sets at sunrise. The Full Moon
phase repeats every 29.531 days - one synodic month.
Lunar eclipses can only occur within a few days of the Full Moon
, but they do not happen at every Full Moon
. This is due to the 5.1 degree tilt of the Moon
around the Earth compared to the Earth's orbit
around the Sun
. The intersection of these two orbits
is the line of nodes, and lunar eclipses occur when this line is pointing towards the centre of the Moon
's motion around the Earth, with the Sun
illuminating only one side of the Earth and Moon