On the measurements of the moon’s infrared temperature and its relation to the phase angle

Radiometric measurements of the thermal radiation originating from the moon’s surface were obtained using an infrared detector operating at wavelengths between 8 and 14 μm. The measurements cover a full moon cycle. The variation of the moon’s temperature with the lunar phase angle was established. The lunar temperatures were 391 ± 2.0 K for the full moon, 240 ± 3.5 K for the first quarter, and 236 ± 3 K for the last quarter. For the rest of the phase angles, the lunar temperature varied between 170 and 380 K. Our results are comparable with those obtained previously at these phase angles. For the new moon phase, the obtained temperature was between 120 and 133 K. With the exception of the new moon phase, our measurements at all the phase angles were consistent with those obtained using Earth-based data and those obtained by the Diviner experiment and the Clementine spacecraft. At the new phase, our measurements were comparable with those obtained from the ground but were significantly higher than those obtained by the Diviner and Clementine data. We attribute this inconsistency to either the calibration curve of our detector, which does not perform well at very low temperatures, or to infrared emission from the atmosphere. A simple linear model to predict the lunar temperature as a function of the phase angle was proposed. The experimental errors that affect the measured temperatures are discussed.