Beyond the answers - interesting background to this quiz

A city at the centre of a global pilgrimage

Mecca, in Saudi Arabia, is the birthplace of Islam and the destination of the Hajj, the annual pilgrimage that every able Muslim is expected to make at least once. During Hajj, millions of people travel to the city, making it one of the largest regular gatherings of humans anywhere on Earth. Non-Muslims are not permitted to enter the city itself, which makes it unusual among major world destinations.

The Caspian's unusual status

The Caspian Sea is the largest inland body of water on the planet, bordered by five countries: Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan. Because it has no outlet to the ocean and sits below sea level, its legal status has been debated for decades - is it a sea or a lake? That distinction matters, because it determines how the resources beneath it, including oil and gas, are shared.

Chile's long, thin shape

Chile stretches over 4,000 km from north to south but averages only around 180 km in width, which explains why it shares land borders with just three countries: Argentina to the east, and Bolivia and Peru to the north. The Andes run along much of its eastern edge, forming a natural boundary with Argentina. This geography gives Chile everything from the driest desert on Earth to glaciers in the south.

Venus and its surprisingly tidy path

Venus has the most circular orbit of any planet in the solar system, with an eccentricity of less than 0.01 - meaning its distance from the Sun barely changes over the course of a Venusian year. By contrast, Mercury and Mars have noticeably elliptical orbits. Venus is also the slowest-spinning planet, taking longer to rotate once on its axis than to complete an orbit around the Sun.

Why 180 degrees never changes

The interior angles of any flat triangle always add up to 180 degrees, no matter how stretched or squashed the shape is. This rule follows directly from the geometry of parallel lines and is one of the first theorems taught in school mathematics. On curved surfaces, however, the rule breaks down - which is part of why cartographers can never flatten the globe onto a map without some distortion.