December 23

1672 – Astronomer Giovanni Cassini discovered Saturn's moon Rhea, the fifth major satellite of the planet.
1954 – The first successful kidney transplant was carried out, done between identical twins.
1968 – Astronauts on Apollo 8 became the first men to orbit the Moon. During ten lunar orbits, the astronauts took star sightings to pinpoint landmarks, surveyed landing sites, took both still and motion pictures and made two television transmissions to Earth. It was also the first manned flight to escape the influence of Earth's gravity.