Planetary phase

A planetary phase is a certain portion of a planet's area that reflects sunlight as viewed from a given vantage point, as well as the period of time during which it occurs.

The two inferior planets, Mercury and Venus, which have orbits that are smaller than the Earth's, exhibit the full range of phases as does the Moon, when seen through a telescope.

Sometimes they appear to cross the solar disk, which is called a transit of the planet.

At intermediate points on their orbits, these planets exhibit the full range of crescent and gibbous phases.

Mars often appears significantly gibbous, it has a maximum phase angle of 45°.