The Moon completes its cycle of phases, and realigns with the Sun once every 29.5 days.
Solar eclipses are more rare than lunar ones, and much more spectacular.
By an amazing coincidence, although the Sun is 400 times the size of the Moon, it is also 400 times further away, meaning that both objects look the same size in our sky. But the exact size of the match means that to see a solar eclipse you have to be in exactly the right place at the right time - the Moon's shadow moves rapidly along a thin strip of the Earth's surface. From the ground, the black disk of the Moon slowly covers over the bright face of the Sun, leaving a shrinking crescent, until it finally reaches 'totality'. This period only lasts for a few minutes at most, but allows a wonderful view of the faint outer regions of the Sun's atmosphere - the 'corona' of thin, superhot gas which streams out along the Sun's magnetic field, and solar flares and 'prominences' looping up from the surface. As the Moon passes on, the first fragment of the bright 'photosphere' to re-emerge turns the Sun into a brilliant 'diamond ring'.