The planets Mercury and Venus have orbits that are nearer to the Sun than the Earth's. Consequently, as viewed from Earth, they are always found near the Sun in the sky. These planets have the "aspects" (specific geometrical configurations of Earth-Sun-planet) of inferior conjunction, superior conjunction, greatest Eastern elongation, and greatest Western elongation. Mercury and Venus are difficult to observe at conjunction because they are near the Sun. They are most easily observed at elongations when they are at their greatest angle from the Sun. At these times they may be observed either just before dawn or just after sunset. This is why Venus is sometimes referred to as the "evening star" or the "morning star".

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