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Five days ago, Sunday morning, I set an alarm and woke up at 3:15am to watch a little spacecraft land on the Moon. This was the "Blue Ghost" lander from Firefly Aerospace. Most of these private Moon landings have ended in failure or limited success, but this one was textbook.

An hour or two after landing (I was in and out of sleep), Firefly Aerospace posted a dramatic photo of the spacecraft's shadow. See below. It appears that they landed on the rim of a small, well-weathered crater. It's just after dawn on the Moon so shadows are long. The almost full Earth is in the sky directly ahead, and the Sun is behind us. Assuming the lander is on the rim, how big is that crater? Basically, this amounts to determining the distance to the shadow. I can think of two ways to do this. They seem to yield somewhat conflicting answers. One note: the horizon looks curved. It shouldn't be. That's an indication that this is a sort of "fisheye" effect in a small, tough camera, probably an off-the-shelf purchase, might be a GoPro.

Try it out. What numbers do you get? How big is that crater?? While it's not really navigating, this puzzle depends on some basic tools of celestial navigation...

A few days after the initial photo, the team released a video that combined imagery captured during descent including the actual moments of touchdown. "Picking up some dust...", the robot pilot might have said. Here's the video.

Frank Reed

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