Fahrenheit in the context of "Temperature scale"

Temperature quantitatively expresses the attribute of hotness or coldness. Temperature is measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making up a substance.

Thermometers are calibrated in various temperature scales that historically have relied on various reference points and thermometric substances for definition. The most common scales are the Celsius scale with the unit symbol °C (formerly called centigrade), the Fahrenheit scale (°F), and the Kelvin scale (K), with the third being used predominantly for scientific purposes. The kelvin is one of the seven base units in the International System of Units (SI).

Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Virtually all of the ice on Earth is of a hexagonal crystalline structure denoted as ice I_h (spoken as "ice one h"). Depending on temperature and pressure, at least nineteen phases (packing geometries) can exist. The most common phase transition to ice I_h occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. When water is cooled rapidly (quenching), up to three types of amorphous ice can form. Interstellar ice is overwhelmingly low-density amorphous ice (LDA), which likely makes LDA ice the most abundant type in the universe. When cooled slowly, correlated proton tunneling occurs below −253.15 °C (20 K, −423.67 °F) giving rise to macroscopic quantum phenomena.

In mathematics, a negative number is the opposite of a positive real number. Equivalently, a negative number is a real number that is less than zero. Negative numbers are often used to represent the magnitude of a loss or deficiency. A debt that is owed may be thought of as a negative asset. If a quantity, such as the charge on an electron, may have either of two opposite senses, then one may choose to distinguish between those senses—perhaps arbitrarily—as positive and negative. Negative numbers are used to describe values on a scale that goes below zero, such as the Celsius and Fahrenheit scales for temperature. The laws of arithmetic for negative numbers ensure that the common-sense idea of an opposite is reflected in arithmetic. For example, −‍(−3) = 3 because the opposite of an opposite is the original value.

Negative numbers are usually written with a minus sign in front. For example, −3 represents a negative quantity with a magnitude of three, and is pronounced and read as "minus three" or "negative three". Conversely, a number that is greater than zero is called positive; zero is usually (but not always) thought of as neither positive nor negative. The positivity of a number may be emphasized by placing a plus sign before it, e.g. +3. In general, the negativity or positivity of a number is referred to as its sign.

Enceladus is the sixth-largest moon of Saturn and the 18th largest in the Solar System. It is about 500 kilometres (310 miles) in diameter, about a tenth of that of Saturn's largest moon, Titan. It is covered by clean, freshly deposited snow hundreds of meters thick, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only −198 °C (75.1 K; −324.4 °F), far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.

Enceladus was discovered on August 28, 1789, by William Herschel, but little was known about it until the two Voyager spacecrafts, Voyager 1 and Voyager 2, flew by Saturn in 1980 and 1981. In 2005, the spacecraft Cassini started multiple close flybys of Enceladus, revealing its surface and environment in greater detail. In particular, Cassini discovered water-rich plumes venting from the south polar region. Cryovolcanoes near the south pole shoot geyser-like jets of water vapour, molecular hydrogen, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totalling about 200 kilograms (440 pounds) per second. More than 100 geysers have been identified. Some of the water vapour falls back as snow, now several hundred metres thick; the rest escapes and supplies most of the material making up Saturn's E ring. According to NASA scientists, the plumes are similar in composition to comets. In 2014, NASA reported that Cassini had found evidence for a large south polar subsurface ocean of liquid water with a thickness of around 10 km (6 mi). The existence of Enceladus's subsurface ocean has since been mathematically modelled and replicated.

A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranus and Neptune are a distinct class of giant planets composed mainly of heavier volatile substances (referred to as "ices"). For this reason, Uranus and Neptune are often classified in the separate category of ice giants.

Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of their mass. They are thought to have an outer layer of compressed molecular hydrogen surrounding a layer of liquid metallic hydrogen, with a molten rocky core inside. The outermost portion of their hydrogen atmosphere contains many layers of visible clouds that are mostly composed of water and ammonia. The layer of metallic hydrogen located in the mid-interior makes up the bulk of every gas giant and is referred to as "metallic" because the very high atmospheric pressure turns hydrogen into an electrical conductor. The gas giants' cores are thought to consist of heavier elements at such high temperatures (20,000 K [19,700 °C; 35,500 °F]) and pressures that their properties are not yet completely understood. The placement of the solar system's gas giants can be explained by the grand tack hypothesis.

HD 209458 b is an exoplanet, specifically a hot Jupiter, that orbits the solar analog HD 209458 in the constellation Pegasus, some 157 light-years (48 parsecs) from the Solar System. It is sometimes informally called Osiris. The radius of the planet's orbit is 0.047 AU (7.0 million km; 4.4 million mi), or one-eighth the radius of Mercury's orbit (0.39 AU (36 million mi; 58 million km)). This small orbital distance results in a year that is 3.5 Earth-days long and an estimated surface temperature of about 1,000 °C (1,800 °F; 1,300 K). Its mass is 220 times that of Earth (0.69 Jupiter masses) and its volume is some 2.5 times greater than that of Jupiter. The high mass and volume of HD 209458 b indicate that it is a gas giant.

HD 209458 b represents a number of milestones in exoplanetary research. It was the first of many categories:

The degree Celsius is the unit of temperature on the Celsius temperature scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the closely related Kelvin scale. The degree Celsius (symbol: °C) can refer to a specific point on the Celsius temperature scale or to a difference or range between two temperatures. It is named after the Swedish astronomer Anders Celsius (1701–1744), who proposed the first version of it in 1742. The unit was called centigrade in several languages (from the Latin centum, which means 100, and gradus, which means steps) for many years. In 1948, the International Committee for Weights and Measures renamed it to honor Celsius and also to remove confusion with the term for one hundredth of a gradian in some languages. Most countries use this scale, with the exception of the United States, some island territories, and Liberia, where the Fahrenheit scale is still used.

Throughout the 19th and the first half of the 20th centuries, the scale was based on 0 °C for the freezing point of water and 100 °C for the boiling point of water at 1 atm pressure. (In Celsius's initial proposal, the values were reversed: the boiling point was 0 degrees and the freezing point was 100 degrees.)