known sightings of mercury date back to at least the first millennium bc. before the 4th century bc, greek astronomers thought that mercury was two different objects: the one that they were only able at sunrise, they called apollo; the other one that they were only able to see at sunset, they called hermes. the english name for the planet is from the romans, who named it after the roman god mercury. the symbol for mercury is based on hermes' staff.