Anyone know what this might be?

Glad you enjoyed it this evening, Nick.

That’s a great image of the Moon.

As regards the “mystery object” it looks like a satellite or perhaps a piece of space debris. There are quite a few south-north satellites and not all are military / spy satellite in origin. Many environmental satellites have this orbital path so that they can cover the whole planetary surface over a period of time.

There will be quite a few rocket bodies as well... and particularly remnants of old Soviet spy satellites.

SkySafari has satellites included in the database now, so that’s a good place to look. Orbitrack is another app that is quite useful for satellite data.

Looking at it again in close-up, the object does appear to be changing shape (though that could be atmospherics)... leading me to suspect that it’s an object that’s tumbling and therefore probably space debris, like a spent rocket booster or rocket body.

Yeah I think you could be right. At higher resolution it definitely appears to be changing shape. Interesting stuff! Thanks mike!

That's a fascinating capture of a mysterious transit, Nick!  And a lovely pan of the moon in its own right. But the final image is fabulous, nice work.   Also, great detective work from both of you!