Facts about science & nature
Science and nature supply facts that feel like they break the rules until you see the mechanism. Hot water freezing before cold, glass that flows, lightning hotter than the surface of the Sun. Each entry keeps the physics or chemistry short and readable, states plainly where the effect is still debated, and links to a source for anyone who wants the full derivation rather than the headline.
A lightning bolt is about five times hotter than the surface of the Sun.
The air in a lightning channel is heated to around 30,000 degrees Celsius in a few millionths of a second. The surface of the Sun is about 5,500 degrees.
Bananas are slightly radioactive.
Bananas are rich in potassium, and a small fraction of all potassium is the radioactive isotope potassium-40. Eating one exposes you to a tiny dose of radiation, which scientists jokingly call a banana equivalent dose.
Under the right conditions, water can boil and freeze at the same time.
At a temperature of 0.01 degrees Celsius and a pressure of about six thousandths of normal air pressure, water reaches its triple point. Ice, liquid water and steam all exist together in equilibrium.
Glass is not a slowly flowing liquid, and old window panes are not thicker at the bottom because they sagged.
The popular story says medieval glass has flowed downward over centuries. In fact, old panes were made by spinning or blowing glass, which produced uneven sheets, and glaziers often put the thick edge at the bottom.
The Amazon carries about a fifth of all the river water that flows into the world's oceans.
Its discharge is greater than the next seven largest rivers combined. The fresh water pushes so far out to sea that early sailors could drink from the ocean more than 100 kilometres from the coast.
Every helium balloon you release is gone for good: helium escapes Earth into space.
Helium is so light that Earth's gravity cannot hold on to it. Once it reaches the upper atmosphere it drifts away, and there is no natural process on Earth that makes more of it in useful amounts.
Diamond and the graphite in a pencil are both pure carbon.
The only difference is how the carbon atoms are arranged. In diamond every atom is bonded rigidly to four neighbours in a three-dimensional lattice; in graphite the atoms form flat sheets that slide over each other, which is why pencils write.
The Dead Sea is so salty that you cannot sink in it.
Its water is about 34 percent salt, nearly ten times saltier than the ocean, and much denser than a human body. Swimmers float on the surface like corks and can read a newspaper lying on their backs.
The largest desert on Earth is not the Sahara. It is Antarctica.
A desert is defined by how little precipitation falls, not by heat or sand. Much of Antarctica's interior gets less than 50 millimetres of precipitation a year, drier than most of the Sahara.
Every rainbow is a full circle. The ground just hides the bottom half.
A rainbow forms at a fixed angle of about 42 degrees from the point directly opposite the Sun. From a plane or a high mountain, with rain below you, the whole circle is sometimes visible.
Sound travels more than four times faster in water than in air.
In air, sound moves at about 343 metres per second. In water it races along at roughly 1,480 metres per second, and in steel at around 5,900.
Under some conditions, hot water freezes faster than cold water, and scientists still argue about why.
The Mpemba effect is named after a Tanzanian schoolboy who noticed in 1963 that his hot ice-cream mix froze before his classmates' cooler ones. Aristotle had described something similar 2,000 years earlier.
The Eiffel Tower is about 15 centimetres taller in summer than in winter.
The tower is made of iron, and metal expands when it is heated. On a hot day the sun-facing side expands more than the shaded side, so the top also leans slightly away from the Sun.
Mount Everest is still growing by a few millimetres every year.
The Indian tectonic plate is pushing into the Eurasian plate at about five centimetres a year, and the Himalayas are being squeezed upward as a result. Everest's official height was revised to 8,848.86 metres in 2020.