is part of the International Astronomical Union
with responsibility for activities related to TIME. Its Terms of Reference are:
- Maintain cooperation with national and international institutions providing atomic timkeeping information.
- Develop cooperation between observatories and other institutions providing and archiving astronomical data relevant to atomic timekeeping, such as pulsar data.
- Develop methods of analysing and evaluating astronomical data relevant to fundamental concepts of time.
- Develop methods of publicising astronomical data and results relevant to time.
The generation of time scales left the astronomical community more than 40 years ago when, in 1967,
the second became defined by an atomic transition in the
International System of Units (SI)
. But time still interacts with astronomy in many ways:
- It acts as the independent variable for the description of all dynamical systems; its stability allows one to study these systems and their perturbations (see Earth rotation, ephemerides, pulsar timing)
- Many observation techniques actually rely on the measurement of the time of propagation of electromagnetic signals; then general relativity theory yields a consistent picture of the astronomical systems under study
- Atomic time scales and modern synchronization methods enable all astronomical events to be dated with adequate uncertainty