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 (+/- 2 deg) across the separate snapshots.

Exposure

This term is used only to organize the UVOT data. An exposure is defined as the time UVOT contiguously observes the target in a particular configuration (mode, window size and filter). Each exposure corresponds to a different extension in the UVOT FITS file.