1) Thermal radiation from objects like stars and galaxies can be used to measure their temperature. The intensity of thermal radiation emitted as electromagnetic waves depends on the object's temperature based on the blackbody spectrum. 2) The blackbody spectrum describes the relationship between an object's temperature and the intensity of the electromagnetic radiation it emits. It allows astronomers to determine the temperature of celestial objects by measuring the intensity of the radiation. 3) Wien's law provides a direct relationship between an object's temperature and the wavelength of peak intensity in its thermal radiation spectrum, allowing temperature to be calculated from measurements of peak wavelength.