The nighttime lunar surface has been scanned at a variety of phases both before and after new Moon. A differential chopping technique was used which records the flux difference between adjacent resolution elements along a scan. In principle the differential scan can be integrated to provide the flux distribution, but slow drifts in the sensor null level frustrated this procedure. However, some cold limb temperatures have been calculated using the planet Jupiter for calibration. The measurements were made with a resolution element of 27 arc seconds on the 28-inch telescope at the University of Arizona. Scan positions were determined by noting features on the illuminated portion of the Moon through a bore-sighted guide telescope. Positional accuracies are within two resolution elements. The technique is particularly sensitive to the detection of nighttime anomalies, and more than 150 of these have been identified. Prior to new Moon is seen large scale thermal structure, corresponding to a previously unknown nonlinear cooling property of the lunar highlands. The nonlinear behavior consistently disappears 3.5 to 4 days after sunset. The effect could be due to the large scale roughness of the highlands or to a significant rock population with a mean size on the order of 10 cm.