gap of semiconductor materials to provide very precise optical (i.e. non-contact) temperature measurements. BET systems require a specialized optical system, as well as custom data analysis software. All objects above absolute zero emit blackbody radiation for which the spectra is directly proportional to the temperature. This property is the basis for a pyrometer or infrared thermometer and thermography. It has the advantage of remote temperature sensing; it does not require contact or even close proximity unlike most thermometers. At higher temperatures, blackbody radiation becomes visible and is described by the colour temperature. For example a glowing heating element or an approximation of a star's surface temperature. Fluorescence Phosphor thermometry Optical absorbance spectra Fiber optical thermometer Electrical resistance Resistance thermometer which use materials such as Balco alloy Thermistor Coulomb blockade thermometer Electrical potential Thermocouples are useful over a wide temperature ranges from cryogenic temperatures to over 1000°C, but typically have an error of ±0.5-1.5°C. Silicon bandgap temperature sensors are commonly found packaged in integrated circuits with accompanying ADC and interface such as I2C. Typically they are specified to work within about —50 to 150°C with accuracies in the ±0.25 to 1°C range but can be improved by binning. Electrical resonance Quartz thermometer Nuclear magnetic resonance Chemical shift is temperature dependent. This property is used to calibrate the thermostat of NMR probes, usually using methanol or ethylene glycol. This can potentially be problematic for internal standards which are usually assumed to have a defined chemical shift (e.g 0 ppm for TMS) but in fact exhibit a temperature dependence. Magnetic susceptibility Above the Curie temperature, the magnetic susceptibility of a paramagnetic material exhibits an inverse temperature dependence. This phenomenon is the basis of a magnetic cryometer. Applications Thermometers utilize a range of physical effects to measure temperature. Temperature sensors are used in a wide variety of scientific and engineering applications, especially measurement systems. Temperature systems are primarily either electrical or mechanical, occasionally inseparable from the system which they control (as in the case of a mercury-in-glass thermometer). Thermometers are used in roadways in cold weather climates to help determine if icing conditions exist. Indoors, thermistors are used in climate control systems such as air conditioners, freezers, heaters, refrigerators, and water heaters. Galileo thermometers are used to measure indoor air temperature, due to their limited measurement range. Such liquid crystal thermometers (which use thermochromic liquid crystals) are also used in mood rings and used