Star trails

Any bright star. Every streak runs the same way and is about the same length.

1. 01

   Tracking stopped or lost

   The mount stopped tracking partway through the night. A mount that reaches its own limit before the software flips just stops, and every sub after that point is trailed.

   FixCheck the flip settings: the mount's own limit has to come later than the software's flip. Confirm the mount reports tracking before you leave the rig to run.

   Session Checklist
2. 02

   Mount not started

   Tracking was never switched on, or the mount was left parked. Every sub of the night is trailed, from the first.

   FixConfirm in the control software that the mount reports tracking before the first sub.

   Session Checklist
3. 03

   Polar alignment far off

   With the polar axis badly misaligned, stars drift fast enough to streak even in short subs.

   FixPolar align with a software routine before imaging.

   Session Checklist
4. 04

   Cable snag that stopped the mount

   A snag mid-frame streaks one sub. A snag that stops the mount trails the rest of the night.

   FixDress cables so nothing is taut at any orientation, with one bundle leaving the moving assembly.

   Session Checklist

• Elongated stars

  Elongated stars are short ovals with a core. A trail is a streak with no core.

• Stars trail partway through a sub

  If each streak starts from a sharp dot, the mount tracked for part of the sub and then something moved it.

• Walking noise

  Walking noise streaks the background of the stack, and the stars in it are round.

One frame shows the trail. Whether tracking stopped mid-session or never started needs the subs in time order and the mount's log.

Round stars in the first sub of the night and the last, and a mount that reports tracking throughout.

No outside source is cited here. The signature, the causes and their order are the atlas’s own, from imaging experience. The order is a judgment of likelihood; no measured frequency is behind it.