Editing Tidal locking (section)

===Locking of the larger body===
{{See also|Synchronous orbit}}
The tidal locking effect is also experienced by the larger body A, but at a slower rate because B's gravitational effect is weaker due to B's smaller mass. For example, Earth's rotation is gradually being slowed by the Moon, by an amount that becomes noticeable over geological time as revealed in the fossil record.<ref>{{cite book
 | first=Imke | last=de Pater
 | date=2001
 | title=Planetary Sciences
 | publisher=Cambridge| isbn=978-0521482196
 | page=34}}</ref> Current estimations are that this (together with the tidal influence of the Sun) has helped lengthen the Earth day from about 6 hours to the current 24 hours (over about 4.5 billion years). Currently, [[atomic clock]]s show that Earth's day lengthens, on average, by about 2.3 milliseconds per century.<ref>{{cite web|last = Ray|first = R.|date = 15 May 2001|url = http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html|archive-url = https://web.archive.org/web/20000818161603/http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html|archive-date = 18 August 2000|title = Ocean Tides and the Earth's Rotation|publisher = IERS Special Bureau for Tides|access-date =17 March 2010}}</ref> Given enough time, this would create a mutual tidal locking between Earth and the Moon. The length of Earth's [[day]] would increase and the length of a [[lunar month]] would also increase. Earth's sidereal day would eventually have the same length as the [[Orbit of the Moon|Moon's orbital period]], about 47 times the length of the Earth day at present. However, Earth is not expected to become tidally locked to the Moon before the Sun becomes a [[red giant]] and engulfs Earth and the Moon.<ref>{{cite book| last1 = Murray | first1 = C. D.|first2 = Stanley F. |last2 = Dermott| title = Solar System Dynamics| date = 1999| publisher = Cambridge University Press| isbn = 978-0-521-57295-8| page = 184 }}</ref><ref>{{cite book| last = Dickinson| first = Terence| author-link = Terence Dickinson| title = From the Big Bang to Planet X| date = 1993| publisher = [[Camden House]]| location = Camden East, Ontario| isbn = 978-0-921820-71-0| pages = 79–81 }}
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For bodies of similar size the effect may be of comparable size for both, and both may become tidally locked to each other on a much shorter timescale. An example is the [[dwarf planet]] [[Pluto]] and its satellite [[Charon (moon)|Charon]]. They have already reached a state where Charon is visible from only one hemisphere of Pluto and vice versa.<ref name=Michaely2017>{{citation | title=On the Existence of Regular and Irregular Outer Moons Orbiting the Pluto–Charon System | display-authors=1 | last1=Michaely | first1=Erez | last2=Perets | first2=Hagai B. | last3=Grishin | first3=Evgeni | journal=The Astrophysical Journal | volume=836 | issue=1 | id=27 | pages=7 | date=February 2017 | doi=10.3847/1538-4357/aa52b2 | bibcode=2017ApJ...836...27M | arxiv=1506.08818 | s2cid=118068933 | doi-access=free }}</ref>