My first glimpse of Titan in real time wasn't through a toy telescope or even through the respectable telescopes that one finds at star parties. It was a hot August in 1995 and I was at Palomar Observatory during Saturn ring plane crossing, that rare time when the bright rings appear edge-on and nearly disappear to reveal the whole of Saturn's six major inner moons, encircling the planet like a string of pearls, suspended on some imaginary scaffolding in the skies. The biggest gem of all was Titan, a ghostly white orb silently looming in space, lit with the soft reflected light of the Sun, inviting us to come closer (Figure 7.1). I had seen much better images from Voyager 1 depicting this mysterious, cloud-enshrouded world, but never had the moon been so palpably close as during this live-action view. I could not have imagined the enchanted world that lurked beneath those clouds.

Titan was discovered in 1655 by Christiaan Huygens (1629–1695), a Dutch astronomer and mathematician who designed and constructed technologically advanced telescopes, which again shows how technology drives science. He is perhaps best known for his discovery that the velocity of light is finite. Huygens even built a refracting telescope with its lenses in the open air – no unwieldy tubes to drag it down (Figure 7.2). But Huygens's clever invention wasn't very practical: it was just too difficult to align, and there was no way of keeping out stray ambient light. Huygens's great discoveries were made with more pedestrian “bread and butter” telescopes. Titan, for example, was discovered with a 12-foot, 50 power telescope that is today surpassed by the typical equipment in a college's observatory.

Most moons of the Solar System appear as fading tenuous blinks of light in the sky, even when seen through a moderately sized telescope. Intently studying these tiny points, astronomers have used their clever tricks through the ages to infer a surprising amount of information. For example, if a rotating moon or planet dims and brightens in a regular fashion, one can be sure – at least if the body is round – that one hemisphere contains materials that are much brighter than the other – perhaps patches of frost.