![]() ![]() George Howard Darwin (1845–1912), the second son of Charles Darwin, the naturalist, was an astronomer-geophysicist who understood quantitatively the generation of the tides in the gravitational fields of tide-raising bodies, which are primarily the Moon and the Sun for Earth he pointed out that the dissipation of tidal energy resulted in a slowing of Earth’s rotation while the Moon’s orbit was gradually expanded. Few are aware, however, that the solid body of Earth also experiences twice-daily tides with a maximum amplitude of about 30 centimetres. The twice-daily high and low tides in the ocean are known by all who have lived near a coast. Since tidal dissipation accounts for the current spin states of several planets, the spin states of most of the planetary satellites and some of their orbital configurations, and the spins and orbits of close binary stars, it is appropriate that tides and their consequences be included in this discussion. Dissipation of part of the energy stored in these tidal distortions leads to a coupling that causes secular changes (always in the same direction) in the orbit and in the spins of both bodies. However, the gravitational field of one body in close orbit about another will tidally distort the shape of the other body. This discussion has so far treated the celestial mechanics of bodies accelerated by conservative forces (total energy being conserved), including perturbations of elliptic motion by nonspherical mass distributions of finite-size bodies. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.
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