What we learned:
Cold temperatures drain the camera’s battery. For most of the hour we thought we were capturing star trails, the shutter had closed because the battery died.
Following this experience, we purchased a used Canon F-1 (used with our telescope shots and for 1999 Iridium flare and leonid photography).
The F-1, with battery removed, operates certain shutter speeds mechanically, including “B” which allows the user to determine length of exposure.