Optical properties of Apollo 11 Moon samples

Lunar powder samples returned by Apollo 11 are remarkably similar in their optical properties to those measured for an area of several square kilometers surrounding Tranquillity base, suggesting a ubiquitous covering of the same material in the region. However, there are minor exceptions to the close match: the powder sample shows large polarizations and a larger opposition effect than would be expected from previous observations. In the spectrum of the lunar rock samples, we detected a strong, broad absorption at 0.92 μ and a weaker band at ≳1.8 μ, which are likely to be caused by Fe 2+ in clinopyroxene. The band near one micron was absent in the powder sample (presumably because the particle sizes were too small), which suggests that the spectrophotometer may become a valuable tool in distinguishing between rocky and dusty areas on the moon.