Astronomy Picture of the Day: Lapetus — Saturn’s “Yin-Yang” Moon: Discovered October 25, 1671!

 

#NASA, #Space, #astronomy, #διάστημα

Black Hole

Iapetus is one of the strangest moons in the Solar System: one hemisphere is brilliantly bright, the other almost black, as if the satellite had been deliberately split into light and dark. That stark contrast earned it the nickname “yin-yang.” On October 25, 1671, the Italian astronomer Giovanni Cassini spotted it for the first time. It was only the second known moon of Saturn — Titan had been discovered by Christiaan Huygens just six years earlier. Cassini could see Iapetus when it was west of the planet, but it repeatedly vanished when it should have been visible to the east. He eventually realized the reason: one hemisphere is far darker than the other, so the moon nearly disappears from view in certain positions. Centuries later, NASA’s Cassini probe sent back detailed images that confirmed this dramatic two-tone appearance. Cassini himself didn’t stop at one discovery — he later found three more major Saturnian moons: Rhea, Tethys, and Dione.