Matter is made up mostly of charged particles which vibrate, rotate, and move. We feel this motion as temperature. The rate and freqency of light emitted depends only on the temperature of the blackbody. The hotter something is, the more light it emits. The frequency range emitted also depends on the temperature.
Higher temperature gives light at higher frequencies.
Most opaque objects roughly approximate a black body, so measuring their emitted light determines their temperature. Blackbody radiation is a form of continuous spectrum . By measuring these shifts in wavelength, we can measure the speed of moving objects. The same process is used to measure automobile speeds using radar. The number of protons in the nucleus determines the chemical element.