Lunar Day Twenty-Three
The slender, silent Moon is once again lit with Earthshine (Fig. 24.1). As we stand here in the moments before dawn, we behold the “New Moon in the Old Moon’s Arms.” We have almost come full circle, have not we? There is still more to learn…
Before daylight comes, we journey to the lunar surface in search of crater Foucault (Fig. 24.2). To find it, head north to landmark Sinus Iridum and locate the punctuation of crater Bianchini in the center of the ring of Juras Mountains. Just northeast, and near the shore of south-eastern Mare Frigoris, look for a bright little circle - crater Foucault. Physicist Jean Foucault played an instrumental role in the creation of today’s parabolic mirrors. His “Foucault knife edge test” made it possible for opticians to test mirror curves for optical excellence during the final phases of shaping before metallization. Thanks to Foucault’s insight, we can turn our telescopes on difficult objects such as double stars…or tiny craters!