Pytheas of Massalia ( Ancient Greek: Πυθέας ὁ Μασσαλιώτης; Latin: Pitheas Massiliae; fl. 4th century BC), was a Greek geographer and explorer from the Greek colony of Massalia (modern-day Marseille). He made a voyage of exploration to northwestern Europe in about 325 BC, but his description of it, widely known in Antiquity, has not survived.
In this voyage he circumnavigated and visited a considerable part of Great Britain. He is the first person on record to describe the Midnight Sun. The theoretical existence of a Frigid Zone, and temperate zones where the nights are very short in summer and the sun does not set at the summer solstice, was already known. Similarly, reports of a country of perpetual snow and darkness (the country of the Hyperboreans) had reached the Mediterranean some centuries before. Pytheas is the first known scientific visitor and reporter of the Arctic, polar ice, and the Germanic tribes. He introduced the idea of distant Thule to the geographic imagination, and his account of the tides is the earliest known to suggest the moon as their cause. Pytheas may have reached Iceland.
Pytheas is a small lunar impact crater located on the southern part of the Mare Imbrium, to the south of the crater Lambert.
It has a sharply defined rim, a hummocky outer rampart, and an irregular interior due to slumping or fall-back. There is a small crater along the northern outer rampart, and a similar crater about 20 km to the west. The crater possesses a small ray system that extends for a radius of about 50 kilometers. It is surrounded by lunar mare that is dusted with ray material from Copernicus to the south.