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Gravitational waves are continuously stretching and squeezing the shape of Earth. Using this fact, LIGO is detecting it by interference of light. But the Sun and Moon's tidal effects are also trying to stretch the Earth. Does this affect the detection of gravitational waves? If so, then how do they eliminate these effects?

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  • $\begingroup$ The time scales of these other effects are different, they don't cause the distance between the mirrors to oscillate with a period of a few hundreds of a second. There are other effects like weak seismic effects that will cause interference. These effects are eliminated via passive and active filtering. What you do is you isolate the system from the Earth using suspension systems as best as you can, these will damp down any signals from the Earth. You also measure the seismic signals and with the known damping factor, you then know what to subtract from the detected signal. $\endgroup$ Aug 5, 2016 at 18:17
  • $\begingroup$ The Sun and Moon cause tides in the Earth's dirt. The LIGO mirrors are supported on that dirt, pick up some of that motion, and the interference pattern is effected. As an extension to your question, what about LISA which will be in free fall in space. Will movements of the Sun, Earth, Moon, or other masses with Schwarzschild gravitational fields (ie: not travelling gravitational waves) effect LISA's interference pattern? $\endgroup$ Aug 5, 2016 at 19:44

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It is a matter of frequency.

Lunar and solar tidal cycles have frequencies about once a day adding or subtracting from Earth's own gravity, so a frequency of about $10^{-5}$Hz

LIGO is trying to detect gravitational waves with a frequency of the order of about $10^2$Hz. A more serious difficulty is eliminating other vibrations of a similar frequency

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  • $\begingroup$ What is the other frequencies interfering with G.waves $\endgroup$ Aug 5, 2016 at 18:29
  • $\begingroup$ Other things interfering with LIGO are trucks hitting potholes, earthquakes, etc. That is why they need multiple, to rule out local effects. $\endgroup$ Aug 17, 2016 at 23:03

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