The Moon under another light

In this Picture of the Week, a solitary antenna points timidly at the Moon. This is not some lonesome telescope, but one of the 66 antennas that together make up the impressive Atacama Large Millimeter/submillimeter Array (ALMA), operated by ESO and its international partners.

Humans have been looking at the Moon for as long as anyone can remember, but our eyes only capture a narrow range of wavelengths: visible light. ALMA is different: it can see light at wavelengths thousands of times longer. When ALMA first pointed towards the Moon back in 2008, we saw a version of our satellite under a new light - literally! The radio waves detected by ALMA did not show the Moon’s grey, coarse surface we are familiar with, but its surface temperature, hotter in the areas facing the Sun.

Since then, ALMA has been looking at other, more distant moons circling other planets. Will ALMA and our cherished satellite ever cross paths again?