Summer on Uranus lasts for 21 years – but so does winter.

Planets, meaning wanderers, are named after Roman deities: Mercury, messenger of the gods; Venus, the god of love and beauty; Mars, the god of war; Jupiter, king of the gods; and Saturn, father of Jupiter and god of agriculture; Neptune, god of the sea.

One year on earth is 365.26 days long. One day is 23 hours, 56 minutes, and 4 seconds long. The extra day in a leap year was introduced to compensate for the discrepancy in the Georgian calendar.

There are more than 326 million trillion gallons of water on Earth.

More than 70% of earth’s dryland is affected by desertification.

A US ton is equivalent to 900 kg (2000 pounds). A British ton is 1008 kg (2240 pounds), called a gross ton.

Hydrogen gas is the least dense substance in the world.

The double-helix structure of DNA was discovered in 1953 by James Watson and Francis Crick. The length of a single human DNA molecule, when extended, is 1.7 metres (5 ft 5 in).

A square piece of dry paper cannot be folded in half more than 7 times.

Since space is essentially empty it cannot carry sound. Therefor there is no sound in space, at least not the sort of sound that we are used to.

The ozone layer averages about 3 millimeters (1/8 inch) thick.

The sun is 330,330 times larger than the earth.

The deepest point in the sea: the Mariana Trench off Guam in the Pacific Ocean; it is 10,9 km (6.77 miles) below sea level.

The tallest waterfalls in the world are Angel Falls in Venezuela. At 979 m (3,212 ft), they are 19 times taller than the Niagara Falls, or 3 times taller than the Empire State Building.

The order of the planets, starting closest to the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.