What Is The Temperature and How To Measure It?
What Is The Temperature and How To Measure It?

Temperature is one of the fundamental measurements in physics, and it’s absolutely crucial to all kinds of life. But at ultra-high and ultra-low temperatures, things can get very weird—as you’ll see. So what is temperature exactly? Well, you know how it feels to stand outside waiting for the bus in cold weather. You also know how a hot bath feels.

What is Temperature?

We use temperature to describe the hotness. But in physics, the temperature is defined as the average kinetic energy of molecules in a substance. If the temperature of a substance is more, then its molecules will have higher kinetic energy.

Temperature is a measure of how hot or cold something is; specifically, a measure of the average kinetic energy of the particles in an object, which is a type of energy associated with motion. But how hot is hot, and how cold is cold? The terms hot and cold are not very scientific terms. If we really want to specify how hot or cold something is, we must use temperature. For instance, how hot is melted iron? To answer that question, a physical scientist would measure the temperature of the liquid metal. Using temperature instead of words, like hot or cold, reduces confusion.

What is Body Temperature?

Body temperature is a measure of how well your body can make and get rid of heat. The body is very good at keeping its temperature within a safe range, even when temperatures outside the body change a lot.

  • When you are too hot, the blood vessels in your skin widen to carry the excess heat to your skin's surface. You may start to sweat. As the sweat evaporates, it helps cool your body.
  • When you are too cold, your blood vessels narrow. This reduces blood flow to your skin to save body heat. You may start to shiver. When the muscles tremble this way, it helps to make more heat.

Your body temperature can be measured in many places on your body. The most common ones are the mouth, the ear, the armpit, and the rectum. Temperature can also be measured on your forehead.

Thermometers show body temperature in either degree Fahrenheit (°F) or degrees Celsius (°C). In the United States, temperatures are often measured in degrees Fahrenheit. The standard in most other countries is degrees Celsius.

What is a normal body temperature?

Normal body temperature is about 98.6 degrees Fahrenheit (°F) or 37 degrees Celsius (°C). The normal temperature often varies from 1° to 2°F (½° to 1°C). A normal temperature is usually lower in the morning and increases during the day. It reaches its high in the late afternoon or evening.

What are Units of Temperature?

Photo: KnowInsiders
Photo: KnowInsiders

Centigrade is the unit of measuring temperature. There are different scales and units which are used for measuring temperature. Among them, the most common are Celsius or centigrade (°C), Fahrenheit (°F), and Kelvin (K). Kelvin is considered as the basic unit of temperature in the International System of Units (SI). Generally, the Celsius scale is used widely in which 0°C and 100°C correspond to the freezing and boiling points of water respectively at sea level. Temperature is measured by a thermometer. In the Fahrenheit scale, 32°F and 212°F correspond to the freezing and boiling points of water. This scale is mainly used in the United States.

Fahrenheit: The first Precise Thermometer

In 1714, the Polish-born Dutch physicist, inventor, and scientific instrument maker Daniel Gabriel Fahrenheit unveiled a mercury-based thermometer. Mercury, a liquid metal, expands and contracts based on the surrounding temperature When Fahrenheit placed mercury in a closed tube marked with a numbered scale, he saw the mercury rise and fall when it was exposed to different temperatures. According to The Royal Society in the United Kingdom, this was the world's first known practical, accurate thermometer.

Fahrenheit had based his invention on Danish scientist Ole Roemer's alcohol-based thermometer. Roemer labeled his temperature scale with zero marked at the temperature where brine (saltwater) froze and 60 as the point at which water boiled, wrote Ulrich Grigull, the late director of the Institute for Thermodynamics at the Technical University of Munich in Germany, in a 1986 conference presentation. The ice melted at 7.5 degrees on the Roemer scale, and a human body registered at 22.5.

Fahrenheit's thermometer, though, was much more accurate. He used the same freezing and boiling reference points as Roemer's scale — referred to in his writings as "Extreme Cold" and "Extreme Hott" — but roughly multiplied the scale by four to divide each marker on the scale into finer increments. On Fahrenheit's scale, wrote Grigull, the four reference points were: 0 (at the combined freezing temperature of brine), 30 (the freezing point of regular water), 90 (body temperature), and 240 (the boiling point of water).

Fahrenheit published a paper describing his scale in the journal Philosophical Transactions in 1724. That same year, Fahrenheit was inducted into the Royal Society, the United Kingdom’s national science academy. Grigull wrote, "His fellowship of the Royal Society resulted in his thermometer, and thereby his scale, receiving particular acceptance in England and consequently later also in North America and the British Empire." Fahrenheit's measurement system, sometimes referred to as part of the imperial system, traveled the world with the British Empire.

However, only a few countries today still use Fahrenheit to measure temperature. The United States and its territories, along with the Bahamas, Palau, Belize, the Cayman Islands, the Federated States of Micronesia, and the Marshall Islands, have stuck with the temperature scale, despite the rest of the world moving to the Celsius scale, according to the online geography resource World Atlas.

After Fahrenheit's death in 1736, the Fahrenheit scale was recalibrated to make it slightly more accurate. The exact freezing and boiling points of plain water, minus the salt, were marked at 32 and 212 degrees Fahrenheit, respectively. Normal human body temperature was marked at 98.6.

Temperatures in Fahrenheit are often expressed as a number followed by ℉, or simply F.

Celsius: A More Scientific Scale

"Anders Celsius should be recognized as the first to perform and publish careful experiments aiming at the definition of an international temperature scale on scientific grounds," wrote Olof Beckman, a solid-state physicist at Uppsala University in Sweden. Celsius was a Swedish astronomer and is credited with discovering the connection between the aurora borealis, also known as the Northern Lights, and the Earth's magnetic field, as well as a method for determining the brightness of stars, according to the U.S. National High Magnetic Field Laboratory.

In a proposal to the Royal Swedish Academy of Sciences in 1742, Celsius proposed a scale based on two fixed points: 0 (the boiling point of water) and 100 (the freezing point of water). Following Celsius' death in 1744, the famous Swedish taxonomist Carl Linnaeus proposed that the fixed points are switched, with 0 indicating the freezing point of water and 100 its boiling point, according to The Legacy of Anders Celsius in JSTOR Daily, a digital library. The scale has also been extended to include negative numbers.

Celsius initially called his scale "Centigrade" from the Latin for one hundred ("centi") degrees ("grade"), because there were 100 points between water freezing and boiling. In 1948, an international conference on weights and measures (Conference General des Poids et Measures) changed the name to "Celsius" in honor of Anders Celsius, according to the U.S. National Institute of Standards and Technology (NIST).

The Celsius scale is part of the metric system, otherwise known as the International System of Units (SI). Temperatures in Celsius can be expressed as a number of degrees followed by the symbols ℃, or simply C.

The Celsius scale has 100 degrees between water boiling and freezing, while Fahrenheit has 180 degrees. This means that a single degree Celsius equals 1.8 degrees Fahrenheit. At -40°, both scales have the same value: -40 C = -40 F.

Kelvin: An Absolute Scale For Scientists

In 1848, British mathematician and scientist William Thomson (also known as Lord Kelvin) proposed an absolute temperature scale, which was independent of the properties of a substance like ice or the human body. He suggested that the range of possible temperatures in the universe far exceeded those proposed by Celsius and Fahrenheit. The concept of an absolute minimum temperature was not new, according to NIST, but Kelvin put an exact number to it: 0 kelvins is equal to -273.15 C.

"Thermodynamic temperature" is distinct from temperatures based on freezing and melting points of fluids, Julia Scherschligt, an expert in vacuum and pressure metrology at the National Institute of Science and Technology in the United States, told Live Science.

"Thermodynamic temperature is absolute, not relative to fixed points. It describes the amount of kinetic energy contained by the particles that constitute a blob of matter, that wiggle and jiggle around at sub-microscopic levels," she said. "As the temperature drops, the particles slow down until at some point, all motion ceases. This is absolute zero, which is the benchmark of the Kelvin scale."

Absolute zero occurs at −273.15 C or −459.67 F. Until recently, scientists thought that humans could not recreate this temperature (because to become that cold, energy would have to be added to the system to cool it, meaning that the system would be warmer than absolute zero). But in 2013, German physicists managed to push particles into paradoxical temperatures below absolute zero.

Which Scale Is Best?

The best scale for measuring temperatures can vary depending on the circumstance, namely the community with whom you are sharing information. Historically, Americans use the Fahrenheit scale for daily life, including for weather and cooking, so it is best to use Fahrenheit measurements in the United States. But most countries use Celsius, so it is better to use that scale across the rest of the globe, and while communicating internationally. Ultimately, the best scale for casual use depends on convention and what people around you are using.

But which scale is the most precise?

"Precision isn't really a feature of a scale," Scherschligt said. Rather, the precision of a measurement depends on the increments given by the thermometer being used and the technique of the person using it. "A number can be measured with arbitrary precision on any scale. But only the kelvin is physics-based, which means it is the most accurate scale."

The Kelvin scale, which is based on the physical properties of any gas, can be calibrated precisely anywhere in the universe with the proper equipment and a universal constant. That’s why scientists often prefer to use the Kelvin scale in their experiments.

What is the Temperature on the Moon?

The average temperature on the Moon (at the equator and mid-latitudes) varies from -298 degrees Fahrenheit (-183 degrees Celsius), at night, to 224 degrees Fahrenheit (106 degrees Celsius) during the day. Because the Moon has no significant atmosphere to block some of the Sun's rays or to help trap heat at night, its temperature varies greatly between day and night.

How Temperature is Measured?

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Photo: KnowInsiders

Temperature is measured with a device called a thermometer. A thermometer works on the principle that when the temperature of a substance rises it expands.

Some materials, like mercury and alcohol, expand more. So, they are used in the thermometers. However, electronic and infrared thermometers are also developed. They use special sensors to measure the temperature instead of mercury or alcohol.

A traditional thermometer measures temperature by containing a fluid that expands at a known rate as it gets hotter and contracts as it gets cooler. As the temperature changes, the liquid within a contained tube moves along a scale on the device. As with much of modern science, we can look back to the ancients for the origins of the ideas about how to measure temperature back to the ancients.

In the first century CE, the Greek philosopher and mathematician Hero (or Heron) of Alexandria (10–70 CE) wrote in his work "Pneumatics" about the relationship between temperature and the expansion of air. After the Gutenberg Press was invented, Hero's book was published in Europe in 1575, its wider availability inspiring the creation of the earliest thermometers throughout the following century.

How Thermometer Invented?

The Italian astronomer Galileo (1564–1642) was one of the first scientists recorded to have actually used a device that measured temperature, though it is unclear whether he actually built it himself or acquired the idea from someone else. He used a device called a thermoscope to measure the amount of heat and cold, at least as early as 1603.

Throughout the 1600s, various scientists tried to create thermometers that measured temperature by a change of pressure within a contained measurement device. English physician Robert Fludd (1574–1637) built a thermoscope in 1638 that had a temperature scale built into the physical structure of the device, resulting in the first thermometer.

Without any centralized system of measurement, each of these scientists developed their own measurement scales, and none of them really caught on until Dutch-German-Polish physicist and inventor Daniel Gabriel Fahrenheit (1686–1736) built him in the early 1700s. He built a thermometer with alcohol in 1709, but it was really his mercury-based thermometer of 1714 that became the gold standard of temperature measurement.

Where is the Highest Temperature in the world?

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Photo: KnowInsiders

On 13 September 2012, the World Meteorological Organisation disqualified the record for the highest recorded temperature, exactly 90 years after it had been established at El Azizia, Libya, with a measurement of 58°Celsius. The official highest recorded temperature is now 56.7°C (134°F), which was measured on 10 July 1913 at Greenland Ranch, Death Valley, California, USA.

As a result of an investigation in 2012, the WMO concluded that the El Azizia record measurement could be inaccurate by as much as 7°C due to a combination of factors including the asphalt-like surface over which the measurement was taken, which is not a fair representation of the native desert soil.

Randy Cerveny, a member of the WMO and professor of geography at Arizona State University, commented in 2012: "This investigation demonstrates that, because of continued improvements in meteorology and climatology, climate experts can now re-analyze past weather records in much more detail than ever before."

He added: "We accept that Death Valley temperature extreme record. Obviously, if any new materials on it surface, we will be prepared to open an investigation, but at this time all available evidence points to its legitimacy."

The air temperature of the aptly named Furnace Creek in Death Valley reaches a staggering average daily high of 115°F - making Death Valley the hottest place on Earth.

It gets even hotter on the ground: a measurement of 201°F was taken on July 15 1972 - just 11 degrees away from the boiling point of water.

One of the reasons Death Valley has the hottest temperature ever recorded is because it is approximately 190 ft below sea level, and the air warms as it gets lower.

In addition to this, there are less than three inches of rain in the desert valley each year.

Interesting facts about temperature

  1. In universe temperatures range from about 3,500,000,000 Kelvin (a supernova) to 3 Kelvin (space).
  2. Sun is known to be a class G yellow star. The average surface temperature of the Sun is 5,600 Kelvin.
  3. Absolute zero is the coldest theoretical temperature. Reaching this temperature substance does not possess any heat energy. It has been defined as zero Kelvin (0 Kelvin) which is found to be equivalent to -273.16 degrees Celsius and -459.69 degrees Fahrenheit.
  4. The temperature of a substance has been defined as a result of the speed at which its molecules move. The theory states that the faster the molecules will move, the higher the temperature of the substance will be.
  5. A very notable fact is that Fahrenheit and Celsius are equal at -40 degrees.
  6. Temperature affects the physical properties of materials whether it is solid, liquid, gaseous, or plasma: density; solubility; vapor pressure, and electrical conductivity.
  7. It affects the rate and extent to which chemical reactions take place.
  8. Temperature affects the amount as well as properties of thermal radiation which emits from the surface of an object.
  9. 57.8 °C (136 °F) is the hottest temperature ever recorded on Earth. It was recorded on September 13, 1922, in Al ‘Aziziyah located in Libya.
  10. −89.2 °C (−128.6 °F) is the coldest temperature ever recorded on Earth. It was recorded at Vostok Station located in Antarctica on July 21, 1983.
  11. Conduction (occurs in solid), convection (occurs in liquid) and radiation (takes place through space) are the three processes of transferring heat from a substance at a higher temperature to one at a lower temperature.
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