The International Astronomical Union divided the celestial sphere into today's 88 official constellations. Prior to this, the list of 48 constellations by the ancient Greek astronomer, Ptolemy, was still the most conclusive description of constellations. Learn more in Constellations, one of the titles in the All About Space Science series. This series examines the history and science of space exploration. It also delves into the careers and technological advancements associated with this exciting field of study.