Almost all observations of the universe
come by collecting light in various wavelengths.
This light can show variations in brightness,
reveal structure in cosmic objects, and contain huge amounts of information
in how its wavelengths are distributed across a spectrum.
Space isn't static, and recording data through a given duration called
Time-Domain Astronomy tracks how details of an object change.
An object can vary, it can move,
or it can do both.
There are three main classes of how an object can vary in time.
Periodic, quasiperiodic, and transient. Periodic change
means there is a regular fixed pattern to the change.
Quasiperiodic means that there is a pattern and the change
or event happens again and again, but not as regularly.
Transient events are less predictable and often happen only once.
These are the hardest to observe because they can be brief and start unexpectedly.