Auroras form when particles from the Sun, steered by Earth's magnetic field, slam into the upper atmosphere. Green, the most common colour, comes from oxygen around 100 to 250 km up. Higher still, oxygen gives off a rarer red. Blue and purple hues come from nitrogen, often along the lower edges of the shimmering curtains.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.