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!

1789 – Discovery of Mimas and Enceladus by William Herschel

I agree with bystander. The moons Tethys and Dione were discovered in 1684.

Mimas and Enceladus were discovered in 1789; therefor the next number in the series is :

1684

It would appear that the famous site that most went to, but didn’t check other sites, is incorrect about the dates of discovery for Tethys and Dione.

1675 – Cassini discovers his namesake division in Saturn’s rings.

?

My guess is the years of discovery of some of Saturn’s moons.

Titan – 1655

Iapetus – 1671

Rhea – 1672

8 moons of Saturn were discovered by direct observation.

1655 Titan discovered by Christian Huygens

1671 – 1672 Tethys, Dione, Rhea, and Iapetus discovered by Giovanni Cassini

1789 Mimas and Enceladus discovered by William Herschel

1848 Hyperion discovered by WC Bond, GP Bond, and William Lassell

Actually 1684 was when Tethys and Dione were discovered

Doh! Got caught up in the first three numbers and forgot to post the next number in the sequence! Well, others have beaten me to it. 😛

Next in sequence is 1789 –

When William Herschel Discovered Mimas, a satellite of Saturn.

1655 = Christiaan Huygens found Titan Saturns Largest satellite.

1671 = Giovanni Cassini discovered Iapetus, one of Saturns moons.

1672 = Giovanni Cassini discovered Rhea, one of Saturns moons.

1674 ? Maybe.

Next no: 1675: Cassini discerned the Cassini Division

And 1684: Cassini discovered Tethys & Dione

Dates:

1655: Hyugens discovered Titan

1671: Cassini discovered Iapetus

1672: Cassini discovered Rhea

Not 1672.16? History trumps math?

’68 -Oxford’s Savilian professor of geometry John Wallis publishes “The Arithmetic of Infinitesmals” which assigns numerical values to spatial indivisibles as a way to include negative and fractional exponents in determining ways to find a square whose area is equal to that of a given circle.

This allowes for Cassini, after discovering Saturn’s satellite Iapetus in ’71, and his discovery of another sattelite (Rhe), and later or earlier, not sure, but to dare to approximate the distance between the sun and Earth, becoming the first to arrive at a close calculation.

Cassini also discovered Tethys and Dione in 1684 after discerning in 1675 the gap in Saturn’s rings, this is later known as Cassini’s Division….

??? am I even close.

I’m liking these Jean!

1789 – Mimas,Enceladus

New planetary satellites came into focus: Saturn’s Titan (Huygens, 1655), followed by Lapetus (1671), Rhea (1672), and Tethys and Dione (1684), all discovered by Cassini.

So, my answer is 1684.

If its right, then it took less than 5 minutes on google… 🙂

1676 – Cassini discovers the Cassini Division between the A Ring and the B Ring.

1678

The development of intergral calculus:

1655: “Arithmetica Infinitorum” [Infinitesimal Arithmetic] by John Wallis

(3 Dec 1616-?) describes infinite series, and advances towards Integral Calculus

1671: James Gregory discovers what we call the Leibniz Series (an

infinite series that sums to pi/4)

1672: “Il Problema della Quadratura del Circolo” [The Problem of

Circle-Squaring] by Pietro Mengoli (1625-?) has an assortment of infinite

series, infinite products, the sum of the reciprocals of traingular

numbers, and the divergence of the harmonic series (i.e. that the sum

increases without limit of 1/1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + …)

Probably not the correct answer but worth a shot.

Left off the last part…

1676: There is a mostly polite but very intense controversy between Newton

and Leibniz as to who invented what parts of Calculus first.

I suspected that it was a moon discovery thing, but I had no idea exactly what moons (or other objects) were discovered on those dates until reading the comments.

Even though I didn’t know the answer (without Googling… and whatever you say I could have Googled that almost instantly just with those dates;)), I still think that these are great puzzles.

1684 – next discovery of a moon(s) of Saturn

1655 – Titan

1671 – Iapetus

1672 – Rhea

1684 – Tethys & Dione

Interesting that they didn’t get these names until 1847 (!) (even after Enceladus and Mimas were discovered in 1789) but were just Saturn I, II etc depending on distance from Saturn, changing numbers as more moons were discovered.

Enjoyable puzzle but pretty easy to find these answers, although I frankly hope the calculus answer above is correct as it shows the most inventiveness (and tricks the rest of us!)

I object. Is googling the new science?