Refers to the radiation intensity of celestial bodies in microwave band, usually expressed in degrees Kelvin. The brightness of microwave spectrum is an important concept in astrophysics, which can be used to study the physical properties and structure of celestial bodies. In microwave astronomy, observing the microwave radiation of celestial bodies can provide information such as temperature, density, velocity and magnetic field of celestial bodies. By measuring the radiation intensity of celestial bodies in different microwave bands.