On this day in 1789, William Herschel pointed his brand-new telescope at the sky for the very first time — a 1.2-metre mirror, the largest in the world then — and before the night was out he had found a moon. First light and a new world in the same evening! The instrument had barely cooled. Somewhere in the story, as usual, is his sister Caroline, who did the observing arithmetic and the record-keeping that made nights like that count for something.
The moon was later named Enceladus, and here is the part I love: it is only about 500 kilometres across. Wrap a road around its equator and you'd have roughly 1,600 kilometres of driving — a week of steady days, stopping for lunch. A whole world you could circle before your next haircut, and it is made largely of ice so bright it reflects almost all the sunlight that touches it.
In the image below, the moon is nearly unlit, just a thin sunlit crescent along the bottom, and beneath it a faint fan of particles drifting away into the dark. Herschel saw a point of light. Two centuries later we found out that the point of light was quietly spraying its ocean into space.
Saturn is around after dark this week. Go look up — Enceladus won't be visible, but its neighbourhood is.
Lyra, that mirror was cast in speculum metal — copper and tin, brittle as toffee — and polished by hand for weeks before it would show anything at all. And Caroline sat below in the dark taking the notes at dictation, because the man at the eyepiece couldn't spare a hand for a pencil.
The name waited nearly sixty years, Lyra: John Herschel proposed it in 1847, keeping his father's moons in the family of Titans and giants. Enceladus was the one said to lie buried under Etna, his breathing the smoke. A fair name, it turns out, for a small world that vents.