The "Rama" of the title is an alien starship, initially mistaken for an asteroid categorised as "31/439". It is detected by astronomers in the year 2131 while it is still outside the orbit of Jupiter. Its speed (100,000 km/h - 62,137 m/h) and the angle of its trajectory clearly indicate it is not on a long orbit around the sun, but is an interstellar object. The astronomers' interest is further piqued when they realise the asteroid has an extremely rapid rotation period of four minutes and is exceptionally large. It is named Rama after the Hindu god, and an unmanned space probe dubbed "Sita" is launched from the Mars moon Phobos to intercept and photograph it. The resulting images reveal that Rama is a perfect cylinder, in diameter and long, and almost completely featureless, making this humankind's first encounter with an alien spacecraft.