Mercury Mercury is the smallest planet in our solar system and the one that is closest to the Sun. It takes Mercury 88 days to complete one revolution in its orbit and it is the speediest of all planets. As a comparatively bright object in the evening or morning sky, Mercury was well known to many of the ancient people. The ancient Greeks associated this celestial body with the swift messenger of the gods, Hermes. They also distinguished between Apollo in its apparition as a "morning star" (low above the eastern horizon, just before sunrise) and Hermes as an evening star (low above the western horizon, just after sunset). However, they realised that the two names referred to the same celestial body.

Mercury is a Roman god, also known as the Roman god of trade, profit and commerce. His name is apparently derived from the Latin merx or mercator, a merchant. He is very similar to the Greek god Hermes and the Etruscan Turms. His temple on the Circus Maximus, on the Aventine Hill, was built in 495 BC. On May 15, the Mercuralia was held in his honor; merchants sprinkled water from his sacred well near the Porta Capena on their heads.