And another - it's in a language which if Boris Johnson gets his way we won't be allowed to speak at home in the UK (ie it's not English), but one which he speaks himself (he's a classicist by training).
OK, since if I don't give the answer sharpish some bright spark here will either know the answer already or Google it, here it is.
The anagram of course stands for: Annulo cingitur, tenui plano, nusquam cohaerente, ad eclipticam inclinato (encircled by a ring, thin and flat, nowhere touching, inclined to the ecliptic). There we are, it's obvious once one knows the answer, isn't it?
The rings of Saturn had been first seen by Galileo in 1610, but with his pioneering but primitive telescope he could not make out what they were - he referred to them as "Saturn's Ears". Then in 1612 he looked again and they had disappeared, which puzzled him mightily (we now know that in 1612 they were precisely edge-on as seen from Earth, and since they are mostly only 10 metres thick there was no way he could have seen them). In 1656 Huygens realised what they were, but since he didn't yet have the evidence to justify his hunch he announced it as an anagram to keep priority on the discovery if anyone else worked it out before he had marshalled and published his evidence which he did in 1658.