Today, the constellation Leo takes center stage. The Sun officially enters the constellation Leo today, although Leo will not be visible at night until next spring. The constellation Leo is one of the 48 ancient constellations recorded in the Almagest, a work by the Egyptian astronomer, geographer and astrologer Ptolemy. The constellation Leo was already known to the Babylonians more than 4,000 years ago, as well as to other civilizations. There are numerous depictions of Hercules wearing the hide of the Nemean Lion over his shoulders and head.