This Demonstration plots the scaled intensity versus frequency for a blackbody at a given temperature. The spectral radiance as a function of frequency is given by Planck's distribution law: . The dashed lines correspond to frequencies measured by the Planck telescope at 857 GHz (blue line), and the Widefield Infrared Survey Explorer: 1.36 THz (green line), 25.0 THz (purple line), 65.2 THz (orange line), and 88.2 THz (red line). Select the "low freq" button to look more closely at behavior for smaller frequencies and choose "high freq" to observe the behavior at a wider range of frequencies.