Data Organization

Snapshot

A snapshot is the time spent contiguously observing a target. This time is shorter than a single orbit due to interruptions from other targets, Earth occultation, and other observing constraints.

Observation

This term is used to organize data in the Swift Data Archive. An observation is a collection of snapshots on a single target where the roll angle remains more or less constant across the separate snapshots.

Exposure

This term is used only to organize the UVOT data into FITS files by mode (image or event) and filter. An exposure is defined as the time UVOT spends in the same general state for all parameters: mode, window size and filter.