99 Fun Facts About Temperature

At what Fahrenheit reading does water boil at sea level?

212 °F holds only at sea level: the boiling point falls by just under 1 °F for every 500 feet climbed, which is why food takes longer to cook in the mountains.

Which of these, like the kelvin, is one of the seven SI base units?

The kilogram. For more than a century it was defined by a platinum-iridium cylinder kept in a vault near Paris; since 2019 it has been fixed by a constant of nature instead, as the kelvin is.

Which everyday point is 273.15 on the Kelvin scale?

Water's freezing point, 0 °C. A kelvin is the same size as a degree Celsius, so converting between the two only shifts the zero by 273.15, down to the coldest temperature possible.

What was the Celsius scale generally called before it was renamed in 1948?

Centigrade, from the Latin for 'hundred', was dropped in 1948 partly because in French the same word named a hundredth of a grade, a unit of angle; the scale took Anders Celsius's name instead.

As of 2025, which American valley holds the official record for Earth's highest air temperature?

Death Valley. Furnace Creek hit 56.7 °C (134 °F) on 10 July 1913; the valley floor lies below sea level between steep mountain walls, so heated air sinks back down and is trapped instead of escaping.

Ray Bradbury's novel Fahrenheit 451 takes its title from the temperature at which what is said to catch fire?

Paper. The title page calls 451 °F 'the temperature at which book paper catches fire and burns', but in tests paper ignites anywhere from about 424 to 475 °F.

As of 2025, where was Earth's lowest directly measured air temperature recorded?

Vostok Station, Antarctica. The then-Soviet base logged −89.2 °C on 21 July 1983, in the depths of the polar night and nearly 3,500 m up on the ice sheet.

Which planet has the hottest surface in the Solar System, even though another orbits closer to the Sun?

Venus. Its thick atmosphere traps heat in a runaway greenhouse effect, holding the surface at about 465 °C, hot enough to melt lead.

Which Siberian settlement recorded −67.7 °C in February 1933?

Soviet texts cited it as a record low through the 1940s, narrowly beating nearby Verkhoyansk.

The louvred box that shades weather-station thermometers was designed by a lighthouse engineer, the father of which Scottish author?

Robert Louis Stevenson. His father Thomas designed the Stevenson screen; the son trained for the family trade of lighthouse engineering, then gave it up to write.

Carl Wunderlich fixed 'normal' body temperature at 37 °C in 1868 from readings taken where on about 25,000 patients?

The armpit. Infections such as tuberculosis were rife among his patients, one reason researchers think his famous average ran a little warmer than healthy people do today.

Which part of the brain acts as the body's thermostat, holding its core near 37 °C?

The hypothalamus. A fever is this thermostat turning its own set point up, which is why you shiver and feel cold while your temperature is actually climbing.

'Paradoxical undressing', stripping off while freezing, is a late sign of which condition?

Hypothermia. It sets in once core temperature falls below 35 °C, and in its late stages a sudden feeling of warmth is thought to make confused victims undress, which only speeds their heat loss.

Which heat illness, with a core temperature above 40 °C, is a medical emergency?

Heat stroke. The body can no longer control its own temperature, which keeps rising; fever drugs such as aspirin don't help, and rapid cooling is the treatment.

When in the daily cycle is human body temperature typically at its lowest?

Late in the night's sleep, typically around 4 to 5 a.m. The body clock then starts warming you up before you wake, and your temperature peaks in the late afternoon.

Which law of thermodynamics, named as an afterthought in the 1930s, underpins the very idea of temperature?

The zeroth law says two bodies each in thermal balance with a third are in balance with each other, which is what lets a thermometer work; the other laws were already numbered, so it had to go in front.

Temperature is, at heart, a measure of the average what of the particles in a substance?

Kinetic energy. Hotter simply means the atoms and molecules are jiggling faster, which is why there is a coldest possible temperature: the point where that motion can be reduced no further.

Which metal has the highest melting point of all, the reason it was used for light-bulb filaments?

Tungsten melts only at about 3,400 °C, so a filament could glow white-hot without melting; even so, old-style bulbs turned far more of their power into heat than into light.

Which way round did Anders Celsius originally number his temperature scale?

Boiling at 0, freezing at 100: by modern eyes his 1742 scale ran upside down. It was turned round within a few years, around the time he died in 1744, with the botanist Carl Linnaeus among those credited.

Fahrenheit adapted his thermometer and scale from which Danish astronomer?

Ole Rømer, the first to measure the speed of light, showed Fahrenheit his thermometers in Copenhagen in 1708; Fahrenheit later multiplied Rømer's numbers by four to get rid of awkward fractions.

What mixture originally defined 0 °F?

Salt and ice: a slush of ice, water and the salt ammonium chloride settles at one steady low temperature, and Fahrenheit took that as the zero of his scale.

Dry ice, which sits at about −78 °C, is the frozen form of which gas?

Carbon dioxide. At normal pressure dry ice never melts into a puddle: it turns straight from solid to gas, which is why theatres use it in fog machines.

Which liquid did Fahrenheit adopt in place of alcohol for his reliable thermometers?

Mercury. Fahrenheit's instruments agreed with one another so well that observers in different places could compare readings, and their popularity spread his temperature scale with them.

Heating milk to about 72 °C for 15 seconds, enough to kill germs without cooking it, is a process named after whom?

Louis Pasteur. He worked out the gentle-heat method in the 1860s to stop French wine from spoiling, and only later was it turned on milk.

In the early 1600s, inventors such as Santorio Santorio turned the thermoscope into a true thermometer by adding what?

A numbered scale. A thermoscope only showed warmer or colder, whereas with marks to read off the physician Santorio could put a figure on his patients' heat; who added one first, he or Galileo's circle, was never settled.

The zone around a star where a planet could hold liquid water is nicknamed after which storybook character?

Goldilocks. Like her porridge, a planet there is neither too hot nor too cold but 'just right' for liquid water on its surface, which is why planet hunters prize worlds found in a star's habitable zone.

Sir James Dewar's 1892 invention for storing liquefied gases is now a household item under which brand name?

Thermos. Dewar never patented his vacuum flask, so when the Thermos company began selling it he lost his court case and made nothing from an invention found in every picnic bag.

Which liquefied gas, boiling at −196 °C, do doctors use to freeze off warts?

Nitrogen. It makes up most of the air around us, yet as a liquid it is cold enough to freeze the wart's cells, which then die and drop away.

Which metal, used in LEDs, melts at about 30 °C, low enough to turn liquid in the palm of your hand?

Gallium. Its melting point, 29.76 °C, is so dependable that it serves as one of the official fixed points used to calibrate the world's thermometers.

Which element has the lowest boiling point of all, turning to gas at just four degrees above absolute zero?

Helium. It boils at about −269 °C, and at normal pressure it never freezes solid however cold it gets; only squeezing it as well can turn it into ice.

A thermocouple produces a temperature-dependent voltage thanks to which effect?

Seebeck. In 1821 Thomas Seebeck saw a compass needle twitch beside a heated junction of two metals and took it for a magnetic effect; it was really an electric current, the principle behind every thermocouple.

What physical principle lets an infrared thermometer read temperature from a distance?

Blackbody radiation. Everything warmer than absolute zero glows with it, mostly in the infrared at everyday temperatures, and the glow strengthens as an object heats up, so a sensor can read a forehead without touching it.

At 0.01 °C, water can boil and freeze at once, a state called what?

Triple point. Ice, liquid water and vapour coexist there in balance at 273.16 K, a state so reproducible that it defined the kelvin itself from 1954 until 2019.

Which outer layer of the Sun is mysteriously far hotter than its visible surface, at over a million degrees?

The corona. It is so faint beside the Sun's glare that it shows to the naked eye only in a total eclipse, and in 2021 NASA's Parker Solar Probe became the first craft to fly through it.

Since 2019, the kelvin has been defined by fixing which constant?

Boltzmann. His constant was given an exact value in 2019, so the kelvin now rests on a fixed number of nature rather than on the behaviour of a sample of water.

As of 2025, the hottest temperature ever created on Earth, over five trillion degrees, was reached inside which machine?

The Large Hadron Collider. In 2012 physicists there smashed lead nuclei together at nearly the speed of light, briefly making a fireball of quark-gluon plasma far hotter than the centre of the Sun.

A system at a 'negative' absolute temperature is, surprisingly, what compared with anything at a positive temperature?

It is hotter. Negative temperatures arise when more particles sit in high-energy states than in low ones, as in a working laser, so on contact heat always flows out of the 'negative' system.

Which effect, found in 1911 in a metal chilled close to absolute zero, makes the magnets in MRI scanners possible?

Superconductivity. Heike Kamerlingh Onnes saw the electrical resistance of a frozen metal abruptly vanish at about 4 K; a coil in that state can carry the huge currents an MRI magnet needs without losing any as heat.

The air around a lightning flash heats to roughly what temperature?

30,000 °C, about five times hotter than the surface of the Sun. The air is heated so fast that it expands explosively, and that shock wave is what we hear as thunder.

Which compound makes chilli peppers taste hot by triggering the nerve sensors that detect real heat?

Capsaicin. It switches on the same nerve sensor that fires at painfully hot temperatures, so the brain reads chilli as a burn although nothing has heated up; tracking that sensor down won David Julius a share of the 2021 Nobel Prize.

The wind chill figure in a weather forecast is calculated from the heat lost by which of these?

Exposed skin. Wind draws heat from a warm body faster than still air, so skin feels colder than the thermometer reads; a pipe or car radiator only cools to the air's temperature sooner, so above freezing no wind can ice it up.

The heat index in US summer forecasts adds which factor to air temperature to say how hot it feels?

Humidity. Sweat cools the body only as it evaporates, and humid air slows that down, so on the heat index a 32 °C day at 70% humidity feels more like 41 °C.

Atoms chilled to within billionths of a degree of absolute zero merge into which exotic state of matter?

A Bose–Einstein condensate. One holds the cold record as of 2025: German physicists dropped a cloud of it down a tower over 100 metres tall and slowed its atoms to 38 trillionths of a degree above absolute zero.

Sound travels fastest through which kind of air?

Warm air. Density and pressure barely matter to the speed of sound, only temperature: it covers about 331 metres a second at freezing and 343 at 20 °C.

In which of these animals does the warmth of the nest decide whether an egg hatches male or female?

Crocodiles. Sex is set in the egg by warmth rather than genes: nests at around 32 °C hatch mostly males and those a couple of degrees cooler mostly females, so a run of hot summers could skew a whole generation.

The hottest temperature physics can describe, like the smallest length and time, is named after which physicist?

Max Planck. The Planck temperature is about 100 million million million million million degrees; beyond it the known laws break down, and only a quantum theory of gravity, which nobody yet has, could say what happens.

The colour of a star reveals its surface temperature, so which colour are the hottest stars?

Blue. A glowing object shifts from red through white to blue as it heats, the opposite of the colours on a tap: in Orion, blue-white Rigel's surface is about three times hotter than red Betelgeuse's.

At what temperature do Celsius and Fahrenheit thermometers give exactly the same reading?

−40. A Fahrenheit degree is only five-ninths the size of a Celsius one, so although Fahrenheit reads 32 higher at zero Celsius, the gap shrinks as both fall and vanishes at forty below.

The kelvin takes its name, via a Victorian physicist's title, from a river in which Scottish city?

Glasgow. William Thomson, who proposed an absolute temperature scale in 1848, taught at its university for 53 years; made a lord in 1892, he took his title from the River Kelvin, which runs through the grounds.

Which metal landmark's top leans up to 18 cm away from the Sun as its sunlit side expands in the heat?

The Eiffel Tower is built of some 7,300 tonnes of puddled iron, which swells on whichever side the sunshine is heating.

Dolbear's law lets you estimate the outdoor temperature by counting the chirps of which insect?

The cricket chirps faster as the air warms, a link physicist Amos Dolbear published in 1897 in an article called The Cricket as a Thermometer.

The 'Year Without a Summer' of 1816, when crops failed across Europe, followed which Indonesian volcano's eruption?

Tambora's 1815 blast, the largest eruption in recorded history, veiled the sky and cooled the world's land by about one degree Celsius.

Which compound in peppermint tricks cold-sensing nerves, so toothpaste feels cool without any drop in temperature?

Menthol switches on TRPM8, the same sensor that fires when nerve endings are genuinely chilled, so the brain reads minty as cold.

Which planet's atmosphere reaches the lowest temperature in the Solar System, though Neptune orbits farther out?

Uranus bottoms out at about −224 °C because, unlike its near twin, it gives off hardly any heat from within, and nobody yet knows why.

A NASA orbiter found a crater colder than Pluto's surface, at −247 °C, in permanent shadow on which world?

The Moon's Hermite crater, near its north pole, never sees sunlight, and in 2009 it gave the coldest reading then measured anywhere in the Solar System.

Which American pioneered quick-frozen food after watching Inuit fishermen flash-freeze their catch in Labrador?

Clarence Birdseye saw that fish frozen in moments, rather than slowly, kept its texture and tasted fresh once it was thawed.

Which kitchen pot cooks food faster by trapping steam so that water boils at about 120 °C instead of 100?

The pressure cooker descends from the steam digester that French physicist Denis Papin invented in 1679 and showed to the Royal Society in London.

Which dessert goes into a very hot oven with ice cream inside, shielded by a poorly conducting coat of meringue?

Baked Alaska survives because whipped egg white carries heat so poorly that the outside sets and colours before the ice cream has time to melt.

Which gemstone conducts heat better than any other natural material, a fact jewellers' probes use to spot fakes?

Diamond pulls heat away so fast that a tester's warmed copper tip cools measurably the instant it touches a genuine stone.

Elephants shed excess body heat through which large body part, laced with a dense web of tiny blood vessels?

Ears work as radiators: warm blood flows through them and sheds its heat, and the African bush elephant, living in the hottest climates, has the largest of all.

Which symptom, known to doctors as pyrexia, is the body raising its own temperature set point to fight infection?

Fever often begins with a feeling of cold, because the body suddenly sits below its new target and tightens its muscles to catch up.

Which unit was defined as the heat needed to warm one gram of water by one degree Celsius?

The calorie was introduced by Frenchman Nicolas Clément in lectures around 1820, and the Calorie printed on food labels is really a thousand of them.

Which Atlantic current, flowing north-east past Florida, keeps north-west Europe milder than its latitude suggests?

The Gulf Stream was mapped by Benjamin Franklin, who had asked a whaling-captain cousin why mail ships from England took weeks longer than merchant ships.

Which Pacific climate pattern did Peruvian fishermen name for its habit of bringing warm water around Christmas?

El Niño is a sustained warming of the central and eastern tropical Pacific that weakens the trade winds and cuts rainfall over eastern Australia.

Which 2015 climate treaty commits nations to try to limit global warming to 1.5 °C above pre-industrial levels?

The Paris Agreement's firm limit is actually well below 2 °C; the 1.5 °C figure is the tougher target that its signatories promised to pursue.

During which centuries-long cold spell did Londoners hold frost fairs on the frozen River Thames?

The Little Ice Age had help from old London Bridge, whose 19 piers slowed the river enough to freeze; an elephant was led across at the last fair, in 1814.

Stella Liebeck's famous lawsuit against McDonald's was about burns from which drink, served at over 80 °C?

Coffee at McDonald's was held at 82 to 88 °C, a heat her lawyers showed could cause third-degree burns within seconds of a spill.

The 1967 NFL title game, played at −26 °C and nicknamed the Ice Bowl, was hosted by which team?

The Green Bay Packers beat Dallas after the referee's metal whistle froze to his lips at the start, and officials could not use their whistles again all game.

Which form of heat transfer drives sea breezes, thunderclouds and the slow churn of rock in Earth's mantle?

Convection moves heat by moving the fluid itself: warmer, less dense material rises while cooler, denser material sinks to take its place.

Sweating cools a person, and panting cools a dog, mainly through which heat-removing process?

Evaporation cools because the highest-energy molecules are the ones that escape, carrying heat they absorbed from the body away with them.

Which property of water, among the highest of any common substance, lets the oceans moderate Earth's climate?

Specific heat is so high for water because the hydrogen bonds between its molecules soak up energy, letting the seas buffer big swings in temperature.

A forgotten cup of tea stops cooling once it matches the room's temperature, reaching a state that physicists call what?

Thermal equilibrium is where heat's one-way traffic ends: it flows from the hotter body to the colder by any route available until the two match.

Which term describes animals such as lizards that rely on sunlight, not body heat, to reach working temperature?

Ectotherms were long labelled cold-blooded, a term scientists have dropped because animals use more than two ways of controlling body temperature.

The decorative thermometer of glass bulbs floating in a liquid-filled tube is named after which Italian scientist?

Galileo found the principle, that a liquid's density shifts with temperature, but the floating-bulb device itself was invented later by a Florentine academy.

Anders Celsius, whose name is on most of the world's thermometers, was a professor of astronomy in which country?

Sweden's Uppsala University made him professor in 1730, and he was the first to link the northern lights to changes in Earth's magnetic field.

Which English brewer's son proved that work turns into heat by spinning a paddle wheel in a barrel of water?

Joule, who ran the family brewery, even planned on his honeymoon to measure whether a waterfall was warmer at the bottom than at the top.

Which engineer designed the first modern air conditioning system in 1902 for a printing company in Brooklyn?

Willis Carrier was solving an air quality problem at the plant, and his system counts as the first because it controlled the air's moisture as well as its heat.

Which French brothers flew the first hot-air balloon in 1783, sending up a sheep, a duck and a rooster?

The Montgolfier brothers chose a sheep, named Montauciel or Climb-to-the-sky, because it was thought a fair stand-in for a human body.

Satellite sensors measured sand at 70.7 °C, far hotter than the air above, in the Lut Desert of which country?

Iran's Lut Desert hit that ground reading in 2005, when the air above was at most 54 °C; a newer analysis of the satellite data put its sand near 81 °C.

Dallol, where a record yearly average of about 35 °C was logged in the 1960s, is a ghost town in which country?

Ethiopia's Dallol lies in the lowlands of the Danakil Depression, where the average daily high across the whole year is a scorching 41 °C.

Which country lost the world heat record in 2012, when experts ruled its 1922 reading of 58 °C invalid?

Libya's reading at ʽAziziya was thrown out partly because the site's damaged instrument had just been replaced by an ordinary, uncalibrated thermometer.

The world's coldest national capital, with a yearly average right around freezing, belongs to which country?

Mongolia's Ulaanbaatar is high, hundreds of kilometres from any coast and under the Siberian anticyclone, giving it a yearly average of about 0.2 °C.

Which warm mountain wind once lifted the temperature in Spearfish, South Dakota, by 27 °C in just two minutes?

The Chinook, which the Blackfoot people call the snow eater, struck on 22 January 1943; later that day the temperature fell back 32 °C in 27 minutes.

Which nebula did astronomers find in 1997 to be colder than empty space, chilled by its own fast-expanding gas?

The Boomerang Nebula's dying star throws off gas at about 164 km/s, and that rapid expansion chills it below the faint background glow of space.

Which layer of the Sun, at roughly 5,500 °C, is the glowing shell that people see as its surface?

The photosphere is overwhelmingly bright to the eye, yet through a strong enough neutral filter it appears as a hueless grey surface.

In which layer of Earth's atmosphere does the air grow hotter with height, as its ozone absorbs ultraviolet sunlight?

The stratosphere is also where airliners cruise in temperate latitudes, riding its lower reaches at about 9 to 12 km up.

Which ocean layer, where warm surface water gives way to the cold deep, can hide a submarine by reflecting sonar?

The thermocline divides the stirred-up mixed layer above from the calm deep water below, and the way sound bends there matters in submarine warfare.

Which American-born count, watching cannon being bored in Munich, argued that heat is motion and not a fluid?

Rumford sank a cannon barrel in water, set a blunted borer grinding and brought the water to the boil, showing that friction's supply of heat seemed inexhaustible.

Which predator's fur gives the best insulation of any mammal, backed up by a heat exchanger in the blood of its legs?

The Arctic fox grows a winter coat that is 70% fine underfur, and it can stand on frozen ground while keeping its paws just above the point where tissue freezes.

Which North American amphibian survives winter with up to two-thirds of its body water frozen into ice?

The wood frog floods its tissues with glucose and urea, which work as antifreeze by limiting how much ice forms and keeping its cells from shrinking.

Which disc-shaped ocean fish is the only one known to keep its whole body warmer than the surrounding water?

The opah stops heat escaping through its gills with a dense net of blood vessels, where warm blood leaving the heart heats the cold blood coming back.

Which tissue, making up about 5% of a newborn baby's body mass, burns fuel purely to make heat without shivering?

Brown fat owes its colour to a dense packing of iron-rich mitochondria, and it is also abundant in mammals that hibernate.

Which daily energy-saving state lets a hummingbird's body temperature fall from 40 °C to below 20 °C until morning?

Torpor slows a hummingbird's metabolism to a fifteenth of its normal rate, and one bird high in the Andes was recorded chilling itself to just 3.3 °C.

The reaction that gives steak and toast their colour and flavour above 140 °C is named after which French chemist?

Maillard first described it in 1912 while trying to reproduce how living things build proteins, and it is a quite separate process from the caramelising of sugar.

Which phenomenon makes water droplets skitter across a very hot pan, riding on a cushion of their own vapour?

The Leidenfrost effect needs a pan above roughly 193 °C; the vapour layer insulates each drop, so it lasts longer than it would on a cooler pan.

The temperature above which a magnet loses its permanent magnetism is named after which French physicist?

Pierre Curie tracked the change in 1895 using strong magnets and precision balances, and soldering irons now exploit the same threshold to hold a steady heat.

Which quantity did Rudolf Clausius name in 1865, modelling the word on 'energy' and a root meaning transformation?

Entropy grew out of Clausius's puzzling over the usable heat that is always lost when work is done, as it is through friction.

Which French engineer's only book, in 1824, gave the first theory of the maximum efficiency of heat engines?

Sadi Carnot published it at his own expense and died of cholera at 36, long before anyone called him the father of thermodynamics.

Which space telescope sits behind a five-layer sunshield that keeps it below −223 °C, cold enough to see faint infrared?

Webb has to be that cold because a warm telescope gives off infrared of its own, which would drown out the faint light it is trying to collect.