Editing Tide (section)

=== Earth tides ===
{{Main|Earth tide}}
Earth tides or terrestrial tides affect the entire Earth's mass, which acts similarly to a liquid [[gyroscope]] with a very thin crust. The Earth's crust shifts (in/out, east/west, north/south) in response to lunar and solar gravitation, ocean tides, and atmospheric loading. While negligible for most human activities, terrestrial tides' semi-diurnal amplitude can reach about {{convert|55|cm|in}} at the Equator—{{convert|15|cm|in}} due to the Sun—which is important in [[GPS]] calibration and [[VLBI]] measurements. Precise astronomical angular measurements require knowledge of the Earth's rotation rate and [[polar motion]], both of which are influenced by Earth tides. The semi-diurnal ''M''<sub>2</sub> Earth tides are nearly in phase with the Moon with a lag of about two hours.{{Citation needed|date=August 2008}}