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Saturn's Moons Javascript Utility

by Adrian R. Ashford and Richard Tresch Fienberg

This article includes a JavaScript utility to help you identify the moons of Saturn in your telescope's eyepiece. You'll find instructions for its use below.

Anyone who looks at Saturn in a telescope will usually notice several pinpoints of light glimmering near the planet. Even a 60-millimeter (2-inch) telescope will show Saturn's brightest moon, Titan, which shines around 8th magnitude and has a thick, smoggy atmosphere that gives it an orange cast. A 15- or 20-centimeter (6- or 8-inch) scope may reveal up to four more satellites close to the planet, all considerably fainter.

But how can you distinguish them from background stars, and how can you tell which moon is which?

Saturn With and Without Moons
Saturn's moons are much fainter than the planet itself. A short exposure (left) captures only the planet and its rings, whereas an exposure long enough to record the moons (right) drastically overexposes Saturn. At the time these images were made, Saturn's brightest moon, Titan, was several ring diameters to the west (right) and outside the field.
Sky & Telescope photos by Richard Tresch Fienberg.
That's where Sky & Telescope's Saturn's Moons JavaScript utility comes in! For any date and time from January 1900 to December 2100, this interactive tool shows the positions of Titan and the next four easiest inner moons to find: 10th-magnitude Rhea, Tethys, and Dione, and 12th-magnitude Enceladus. Moreover, the utility can match the view through your telescope's optical system whether it shows the sky with north up or south up, and correct or mirror-reversed.

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