Cold refers to the condition or perception of having low temperature; it is the absence of heat or warmth. Many things are associated with cold, such as ice and the color blue. Fluids used to cool objects are commonly called coolants.

The coldest possible theoretical temperature that can be reached is absolute zero, which is 0K on the Kelvin scale, a thermodynamic temperature scale, and −273.15° on the Celsius scale. Absolute zero is also precisely equivalent to 0° R on the Rankine scale (also a thermodynamic temperature scale), and −459.67 degrees on the Fahrenheit scale.

Cooling

Main article: Refrigeration

Cooling refers to the process of becoming cold, or lowering in temperature. This could be accomplished by removing heat from a system, or exposing the system to an environment with a lower temperature.

Air cooling is the process of cooling an object by exposing it to air. This will only work if the air is at a lower temperature than the object, and the process can be enhanced by increasing the surface area of decreasing the mass of the object.

Another common method of cooling is exposing an object to ice, dry ice, or liquid nitrogen. This works by convection; the heat is transferred from the relatively warm object to the relatively cold coolant.

Notable cold locations and objects

• The Boomerang Nebula is the coldest known natural location in the universe, with a temperature that is estimated at 1K (kelvin) (−272.15 °C/−457.87 °F).^[1]
• Herschel Space Observatory instruments and detectors are kept at temperatures below 2 K, using large helium tank for cooling. ^[2]
• The Universe is bathed in electromagnetic radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.725 kelvin.^[3]
• Neptune's moon Triton has a surface temperature of -235 °C (-390 °F).
• Uranus with an atmospheric temperature of -215 °C (-355 °F).^[4]
• Saturn with a temperature of -175 °C (-285 °F) at cloud tops.^[5]
• Mercury, despite being close to the Sun, is actually cold during its night, with a temperature of about -170 °C (-275 °F). Mercury is cold during its night because it has no atmosphere to trap in heat from the Sun.^[6]
• Jupiter with a temperature of -145 °C (-230 °F) at the cloud tops.^[7]
• Mars has a temperature of about -125 °C (-195 °F).^[8]
• The coldest continent on Earth is Antarctica.^[9] The coldest place on Earth is the Antarctic Plateau,^[10] an area of Antarctica around the South Pole that has an altitude of around 3000 meters. The lowest reliably measured temperature on Earth of −89.2 °C (−128.6 °F) was recorded there at Vostok Station on 21 July 1983^[11] (See List of weather records).
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