A scheduled period of data collection by gravitational wave detectors.An observing run is a scheduled period of data collection by gravitational wave detectors, during which the instruments operate continuously to capture signals from cosmic events. These runs are the primary operational mode of observatories like LIGO and Virgo, typically lasting several months to a year. During an observing run, the detectors are tuned to maximum sensitivity, and data are streamed to analysis pipelines that search for gravitational wave candidates in real time.
The first observing run (O1) of Advanced LIGO took place in 2015 and led to the first direct detection of gravitational waves in September 2015. Subsequent runs (O2, O3, O4) have increased sensitivity and detection rates, with Virgo and KAGRA joining the network.
Observing runs are carefully planned to maximize scientific output. Before a run, detectors undergo calibration and commissioning to reduce noise. During the run, data are recorded with timestamps and auxiliary channels to monitor environmental disturbances. Real-time analysis pipelines, such as GstLAL or PyCBC, filter the data for signals matching predicted waveforms from compact binary mergers. Candidate events trigger alerts to the astronomical community for follow-up observations across the electromagnetic spectrum.
Observing runs are the backbone of gravitational wave astronomy, enabling the detection of black hole and neutron star mergers, the measurement of the Hubble constant, and tests of general relativity in strong-field regimes.
During the third observing run (O3), which lasted about 11 months, LIGO and Virgo detected 79 candidate gravitational wave events, more than tripling the number of detections from previous runs combined.











