LIGO Event Trigger Timing Sensitivity
LIGO was designed to detect a tiny ripple in Earth's crust caused by a gravitational wave from a distant inspiral merger.
The LIGO 'trigger timing' is interesting; this trigger determines when LIGO will declare a gravitational wave detection event.
There is a pattern for a trigger for LIGO detections.
The timing of tidal events is related to the Earth's rotation and the revolution of the moon around the Earth. If the moon was stationary in space, the tidal cycle would be 24 hours long. However, the moon is in motion revolving around the Earth. One revolution takes about 27 days and adds about 50 minutes to the tidal cycle. As a result, the tidal period is 24 hours and 50 minutes in length.
The second factor controlling tides on the Earth's surface is the Sun's gravity. The height of the average solar tide is about 50% the average lunar tide. At certain times during the moon's revolution around the Earth, the direction of its gravitational attraction is aligned with the Sun's. During these times the two tide producing bodies act together to create the highest and lowest tides of the year. These spring tides occur every 14-15 days during full and new moons.
The combination of the ocean tide and Earth's rotation results in essentially a slow wave moving across the ocean's surface over the course of a day.
Earth tide is the displacement of the solid earth's surface caused by the gravity of the Moon and Sun. Its main component has meter-level amplitude at periods of about 12 hours and longer.
A new moon or full moon cause a significant earth tide with the Sun also aligned. A perigee has an earth tide regardless of the Sun.
The Earth's crust is solid, unlike the fluid oceans. This disturbance is spread across many square miles but it cannot begin or end smoothly like a fluid.
However it is essentially a slow wave in the crust.
This wave is affecting LIGO which is looking for a gravitational wave affecting the crust.
All LIGO gravitational wave detection events are within a few days of an earth tide event.
One result that no one seems to notice there are gaps of about a week between a set of events barely separated by a few days.
The reason for this is the moon completes in cycle in about 29 days so there is either full moon separated by about 14 1/2 days. LIGO can report multiple detections before or after the peak of each moon event so the larger gap fills with a few events.
Since LIGO began reporting, within any span of a few weeks there will be more LIGO events than earth tide events.
This observation implies the high sensitivity the LIGO system was designed to be. The result is multiple detections before and after the peak of that single earth tide event.
Rather than repeating the data please click here to get the LIGO detection event trigger data.
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Last updated (10/03/2019)
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