This graph shows the temperature above the surface of Mars at three different points in time: Sol 5, late afternoon; Sol 6, mid-morning; and Sol 7, early afternoon (Sol 5 occurred on the night of January 7/8, 2004). These temperature profiles were derived from data taken by the mini-thermal emission spectrometer onboard the Mars Exploration Rover Spirit. By measuring the brightness of the carbon dioxide gas that makes up the martian atmosphere, scientists can deduce the surface temperature above Mars between 20 meters (65 feet) and 2 kilometers (1.2 miles). The observations show large changes in atmospheric temperature both as a function of time of day, and as a function of height near the surface.