The earth is the third planet from the centre of our Solar System, orbiting the Sun. The Moon is a natural satellite of the Earth, orbiting it in a circular orbit. The moon is in eastern quadrature at first quarter. On the sky's dome, the sun is 90º east. A last quarter moon, on the other hand, is the same as a moon in western quadrature, when the moon is 90 ° west of the sun.