Universe Puzzle No. 2

To start your working week, here’s a little something to help you sharpen your brain (OK, it’s already the end of the day for our viewers in New Zealand and Australia, so for you a little pick-me-up after a hard day’s work).

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. And a reminder: this is a puzzle on a “Universal” topic – astronomy and astronomers; space, satellites, missions, and astronauts; planets, moons, telescopes, and so on.

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.

What’s the next number in the sequence? 1655, 1671, 1672

Post your guesses in the comments section, and check back on Wednesday at this same post to find the answer. To make this puzzle fun for everyone, please don’t include links or extensive explanations with your answer, until after the answer has been given. Good luck!

PS There’s an open question on last week’s puzzle too (scroll down to the bottom of the comments).

UPDATE: Answer has been posted below.

Was this too easy perhaps? Maybe only five minutes’ spent googling was all that was needed to find the answer?

Christiaan Huygens discovered the first known moon of Saturn. The year was 1655 and the moon is Titan.

Giovanni Domenico Cassini made the next four discoveries: Iapetus (in 1671), Rhea (in 1672), …

… and Dione (in 1684), and Tethys (also in 1684).

What about Cassini’s discovery of the Cassini Division, in 1675?

Well, the discovery in 1655 was not made by Cassini, the rings of Saturn were discovered by Galileo (in 1610), and so on.

So, no, 1675 is not the next number in the sequence.

So the answer is: 1684

Source: JPL/NASA

It’s amazing to reflect on how much more rapid astronomical discovery is, today, than back then; 45 years from the discovery of Saturn’s rings to Titan, another 20 to the discovery of the Cassini Division; 16 years between the discovery of Titan and Iapetus; … and 74 years from the rings to Dione and Tethys.

And today? Two examples: 45 years ago, x-ray astronomy was barely a toddler; and 74 years ago radio astronomy had just begun. Virtually all branches of astronomy outside the visual waveband went from scratch to today’s stunning results in less time than elapsed between the discovery of Saturn’s rings and its fourth brightest moon!

Check back next week for another Universe Puzzle!