Intervalometer
A timer, built in or external, that fires the shutter automatically at set intervals for a set number of frames.
Measured in
seconds
In depth
An intervalometer makes time-lapse and long unattended sequences possible, and it is also the tool for star trails shot as many short exposures rather than one long one. The interval must exceed the exposure time plus the write time, or frames will be dropped and the resulting motion will stutter.
Examples in practice
Setting a 30-second exposure with a 33-second interval leaves the camera time to write each file before the next.