Nature
Auroras are painted by oxygen and nitrogen
Solar particles slam into the upper atmosphere and excite gas atoms. Oxygen gives green and deep red, nitrogen adds blue and violet — colour tells you the altitude.
More in Nature
Honey never spoils
Low moisture, high acidity and natural hydrogen peroxide make honey hostile to microbes. Sealed pots from ancient Egypt are still edible.
The Sahara was green just 6,000 years ago
Grasslands, lakes and hippos covered North Africa during the African Humid Period. A slow wobble in Earth's orbit shifted the monsoon and the desert took over.
Bananas are berries, strawberries are not
Botanically a berry grows from one flower with one ovary and seeds inside. Bananas qualify; strawberries are "accessory fruits" with seeds on the outside.
Antarctica is the largest desert on Earth
A desert is defined by rainfall, not heat. Antarctica gets so little precipitation that it beats the Sahara for the title.
Most light in the ocean is made by animals
Around three quarters of deep-sea creatures glow. Bioluminescence is used to hunt, hide, and signal in a world with no sunlight.
The largest living thing by volume is a tree
General Sherman, a giant sequoia, holds about 1,487 cubic metres of wood and is still adding the equivalent of a whole tree every year.