If you‘re in the market for a podcast recommendation, here it is: go listen to 13 Minutes to the Moon, produced by the BBC World Service. It‘s an in-depth walk-through of topics around the nearly 13 minute-long final descent1 of the Eagle lander from the Columbia command module down to the surface of the Moon.
I have read about, listened to, and watched tons of material about this expedition. But one thing I learned from listening to episode 9 of the series was that the landings in all cases have been expressly planned to happen in a region close to the terminator when the Moon was in a waxing phase2.
Thanks to the low position of the sun (in the back of the LEM) over the horizon, the overall amount of light was reduced and the structures on the surface cast long shadows. These create contrasting markers in the blinding whiteness to assist the LEM pilots in recognizing and avoiding potential obstacles that might be a hazard to the landing procedure.
In hindsight, it seems totally natural and obvious to plan the landings this way, but it never actually occurred to me until I listened to 13 Minutes to the Moon.
- That inspired the title of the podcast series ↩
- This conclusion is also backed up by the flight path of the mission, see e.g this illustration. ↩