Got circles on the brain today? It’s Pi Day — (3/14 for those of us on the west side of the pond) and a celebration of math and science – as well as the infinite and irrational! It is also Albert Einstein’s birthday. What’s Pi? Π is the 16th letter in the Greek alphabet and is used to represent a mathematical constant, the ratio of a circle’s circumference to its diameter, approximately equal to 3.1415… In basic mathematics, Pi is used to find area and circumference of a circle. You might not use it yourself every day, but Pi is used in most calculations for building and construction, quantum physics, communications, music theory, medical procedures, air travel, and space flight, to name a few. A pi transfer uses the gravity of Saturn’s largest moon, Titan, to alter the orbit of the Cassini spacecraft so it can gain different perspectives on Saturn and achieve a wide variety of science objectives. During a pi transfer, Cassini flies by Titan at opposite sides of its orbit about Saturn (i.e., Titan’s orbital position differs by pi radians between the two flybys) and uses Titan’s gravity to change its orbital perspective on the ringed planet.