Categories: Astronomy

Universe Puzzle No. 4

As with last week’s Universe Puzzle, something that cannot be answered by five minutes spent googling, a puzzle that requires you to cudgel your brains a bit, and do some lateral thinking. This is a puzzle on a “Universal” topic – astronomy and astronomers; space, satellites, missions, and astronauts; planets, moons, telescopes, and so on.

What’s the next number in the sequence? 401, 172, 85.2

There are no prizes for the first correct answer – there may not even be just one correct answer – posted as a comment (the judge’s decision – mine! – will be final), but I do hope that you’ll have lots of fun.

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Post your guesses in the comments section, and check back on Wednesday at this same post to find the answer. Good luck!

UPDATE: Answer has been posted below.

42.5 is the answer; it’s the mean orbital period of Io, in hours; the first three members of the sequence are the mean orbital periods of Callisto, Ganymede, and Europa (source)

Well done scibuff!

Check back next week for another Universe Puzzle.

Jean Tate

Hi! When I was only six (or so), I went out one clear but windy night with my uncle and peered through the eyepiece of his home-made 6" Newtonian reflector. The dazzling, shimmering, perfect globe-and-ring of Saturn entranced me, and I was hooked on astronomy, for life. Today I'm a freelance writer, and began writing for Universe Today in late 2009. Like Tammy, I do like my coffee, European strength please. Contact me: JeanTate.UT@gmail.com