The Ptolemaic dynasty was a Hellenistic royal family which ruled the Ptolemaic Empire in Egypt for nearly 300 years, from 305 BC to 30 BC.

Ptolemy, a somatophylax, one of the seven bodyguards who served as Alexander the Great’s generals and deputies , was appointed satrap of Egypt after Alexander’s death in 323 BC. In 305 BC, he declared himself King Ptolemy I, later known as “Soter” (saviour). The Egyptians soon accepted the Ptolemies as the successors to the pharaohs of independent Egypt. Ptolemy’s family ruled Egypt until the Roman conquest of 30 BC.

All the male rulers of the dynasty took the name Ptolemy. Ptolemaic queens, some of whom were the sisters of their husbands, were usually called Cleopatra, Arsinoe or Berenice. The most famous member of the line was the last queen, Cleopatra VII, known for her role in the Roman political battles between Julius Caesar and Pompey, and later between Octavian and Mark Antony. Her suicide at the conquest by Rome marked the end of Ptolemaic rule in Egypt.

In cosmology, the Copernican principle, named after Nicolaus Copernicus, states the Earth is not in a central, specially favoured position.[1] More recently, the principle is generalised to the relativistic concept that humans are not privileged observers of the universe.[2] In this sense, it is equivalent to the mediocrity principle, with significant implications in the philosophy of science.