Stacking
Lining frames up and adding them together, and what goes wrong when they won't line up. Oldest first, so it reads from the first try to the latest.
Andromeda from both sides of the sky, the Pleiades and Saturn
The polar alignment I thought was 0.2 degrees was really 3, the camera's short exposures got fixed, and an hour and a half of Andromeda came out of two runs stitched across the meridian.
Mapping the garden, and finding home
The telescope measured my garden's skyline by itself before dark, the true home position turned out to be ten degrees from where I had been setting it, Tabby's star got its first night, and then the camera started misbehaving and a neighbour's bonfire finished the night.
Stacking
Astrophotography