Beyond the answers - interesting background to this quiz

The ringed giant that stole the show

Saturn's rings are made mostly of water ice, ranging from tiny grains to boulders, and they stretch thousands of kilometres across while staying remarkably thin. Jupiter, Uranus and Neptune all have ring systems too, but none come close to Saturn's scale or brightness. That is why Saturn is the one most people picture when they hear the word "rings".

A playwright who reshaped American theatre

Tennessee Williams wrote "A Streetcar Named Desire", a play that premiered on Broadway in 1947 and won him the Pulitzer Prize for Drama the following year. Its central character, Blanche DuBois, became one of the most quoted figures in American theatre. Williams drew heavily on his own Southern upbringing, and the play's raw treatment of desire and decline helped change what mainstream audiences would accept on stage.

The anatomy of the iris

The iris is the coloured ring around the pupil in the eye, and its muscles control how much light reaches the retina. Its colour comes from the amount and distribution of melanin, which is why eye colour varies so widely between people. The word itself comes from the Greek word for rainbow, a nod to the range of shades it can take.

A number with only two divisors

A prime number can be divided evenly only by 1 and itself. The number 3 fits that rule, while 63 and 33 are both divisible by 3. Primes are the building blocks of whole numbers, since every integer greater than 1 can be broken down into a unique product of them. That property is what makes primes so valuable in cryptography.

From Gandhi to the Terminator

Mahatma Gandhi was assassinated in 1948, less than a year after India gained independence, by a Hindu nationalist who opposed his stance on partition. Arnold Schwarzenegger, meanwhile, built a very different kind of fame, first as a bodybuilder and then as the star of "The Terminator" in 1984. Two figures from completely different worlds, yet both became shorthand for an era.