... Comet Halley's Nucleus . ... While probably formed at the same time as Io, the difference between the surfaces of these two moons of Jupiter could hardly be greater. ... In 1994, Clementine spent 70 days in lunar orbit mapping the Moon's surface. ... Red stars are cool, with temperatures of around 3,000 degrees Kelvin (K), while blue stars are hotter and can have temperatures over 30,000 degrees K. Our own lovely yellow Sun's temperature is a comforting 6,000 degrees K. Star Trails in Northern Skies...