50 Fun Facts About Temperature

At what Fahrenheit reading does water boil at sea level?

On the same scale water freezes at 32 °F, a 180-degree span versus Celsius's 100.

The kelvin is one of how many SI base units?

The unit name is spelled with a lower-case k, and since 2019 it is defined through the Boltzmann constant.

By what exact offset do the Celsius and Kelvin scales differ?

A one-degree Celsius step equals a one-kelvin step; only the zero point moves.

What was the Celsius scale formerly called?

The name came from the 100-degree interval between water's freezing and boiling points.

What is the officially recognised highest air temperature ever recorded on Earth?

Furnace Creek Ranch in Death Valley logged it on 10 July 1913; a higher 1922 Libyan reading was decertified in 2012.

In which country was a 1922 temperature record decertified after 90 years?

The 57.8 °C reading at ʽAziziya was thrown out in 2012, handing the record back to Death Valley.

Where was the lowest natural ground-level temperature on Earth recorded, in 1983?

The then-Soviet base registered −89.2 °C on 21 July 1983.

What was the record low reading at Vostok Station in July 1983?

Satellites have since spotted ice surfaces near −98 °C, but those are not counted as official thermometer records.

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 standard air-temperature measurement is taken at what height above ground?

The thermometer must also be shielded from direct sunlight.

Who set the long-quoted 'normal' human body temperature of 37 °C in 1868?

His book put temperature charts into clinical use; newer studies put the average nearer 36.4 °C.

21st-century studies put the average internal human temperature at what value?

Analyses published in 2017 and 2020 put it near 36.4 °C, below the 37 °C set by Wunderlich in 1868; body temperature also dips lowest about two hours before waking.

At what core temperature does hypothermia begin?

Intense shivering, numbness and bluish skin mark the threshold.

Hyperthermia at or above what temperature is a life-threatening emergency?

Fever-reducing drugs are useless for it; cooling and rehydration are the treatment.

When during the day is human body temperature typically lowest?

The cycle is governed by the circadian rhythm.

Who proposed the absolute scale that uses Fahrenheit-sized degrees, in 1859?

One Rankine degree equals one Fahrenheit degree, and 0 °R is absolute zero.

On the Réaumur scale, at how many degrees does water boil?

The scale is also known as the 'octogesimal division' for that reason.

What liquid did Réaumur use in his original thermometers?

He liked that it expands more visibly, but its low boiling point made the bulky instruments impractical.

Which direction did Anders Celsius originally run his scale?

Jean-Pierre Christin proposed flipping it a year later and called the result centigrade.

Fahrenheit adapted his thermometer and scale from which Danish astronomer?

Fahrenheit's key change was switching the liquid to mercury.

What mixture originally defined 0 °F?

Fahrenheit's upper fixed point was healthy body temperature, set at 96 so it divided by 12.

Fahrenheit set body temperature at 96 °F so the number would be divisible by what?

As body temperature varies, the scale was later changed to use a different upper fixed point.

In which year did Fahrenheit invent his reliable mercury thermometer?

He proposed the scale that bears his name ten years later, in 1724.

Which ancient physician proposed measuring hotness and coldness in 'degrees'?

His reference point was a mix of equal parts ice and boiling water, with four degrees of heat above and four of cold below.

Who published the first thermoscope drawing with a scale, in 1625?

It was an air thermometer: a bulb of air atop a tube whose lower end opened into water.

Early air thermometers had what awkward flaw?

Being sensitive to air pressure, they were unreliable until sealed liquid-in-glass designs appeared.

What liquid filled the first described sealed thermometer, in 1629?

Joseph Solomon Delmedigo, a student of Galileo and Santorio in Padua, published the description.

Which Florentine academy actually invented the so-called Galileo thermometer?

Galileo's pupil Torricelli was among its members; an Italian nickname for the device was termometro lento, the slow thermometer.

Which London institution revived the Galileo thermometer as a product in the 1990s?

The floats in the modern version rise and fall as the liquid's density changes with temperature.

A maximum-minimum thermometer is also known by whose name?

The original design uses mercury only as an indicator for a column of alcohol that does the measuring.

Below what temperature does mercury become solid, limiting mercury thermometers?

For colder readings a mercury-thallium alloy that stays liquid to −61.1 °C can be used.

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

Thomas Johann Seebeck first noticed a magnetic needle deflect near a heated junction of two metals in 1821.

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

Every object above absolute zero emits it, with a spectrum that tracks temperature.

What is the triple point of water on the Kelvin scale?

Until 2019 the kelvin was defined so that this value was exact; it is now an experimentally measured constant.

Who first used the term 'triple point', in 1871?

He was Lord Kelvin's brother.

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

The triple point of water, the previous anchor, became something to be measured rather than defined.

In which year did the SI stop defining the kelvin via the triple point of water?

From 1954 until then, the triple point was the second fixing point after absolute zero.

If a system at negative absolute temperature touches an ordinary one, heat flows how?

Heat flows from the negative-temperature system to the positive one; laser population inversion is a classic example.

Who first predicted the possibility of negative temperatures, in 1949?

He was studying 2D vortices confined in a finite area when he realised their phase space must be bounded.

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

The sudden expansion of that superheated air is what we hear as thunder.

Wind chill tables were first developed by Siple and Passel working where?

They timed how fast water in a small plastic bottle froze while it hung in the wind on a hut roof.

Can wind chill freeze water pipes when the air temperature is above freezing?

Wind chill describes how cold skin feels, not how cold things get.

What is used instead of wind chill when the apparent temperature is above the air temperature?

Wind chill values are always lower than the air temperature where the formula applies.

What is the lowest temperature ever attained in a laboratory experiment?

That is 38 trillionths of a kelvin; absolute zero itself can never be reached.

Sound speed in a gas is proportional to what function of its absolute temperature?

That relation lets a sound-speed measurement give a very precise gas temperature.

Roughly how many times per second does lightning strike somewhere on Earth?

That adds up to nearly 1.4 billion flashes a year, about 70% of them over tropical land.

At the hottest temperature physics can describe, radiation's wavelength equals what?

No known physics describes anything hotter; a quantum theory of gravity would be needed.

Which law links a black body's peak radiation frequency directly to its temperature?

It is why the colour of a glowing object tells you how hot it is.

The International Temperature Scale of 1990 extends from 0.65 K up to about what?

That upper end is roughly 1,085 °C, the freezing point of copper.

In what year did Lord Kelvin publish his proposal for an absolute temperature scale?

He built it on Carnot's theory, before the first law of thermodynamics had even been formulated.