Editing Lunar Laser Ranging experiments (section)

==Results==
Lunar laser ranging measurement data is available from the Paris Observatory Lunar Analysis Center,<ref>{{cite web |url=http://polac.obspm.fr/llrdatae.html |title=Lunar Laser Ranging Observations from 1969 to May 2013 |publisher=SYRTE Paris Observatory |access-date=3 June 2014}}</ref> the International Laser Ranging Service archives,<ref>{{Cite web|title=International Laser Ranging Service|url=ftp://cddis.gsfc.nasa.gov/pub/slr/data/npt_crd/}}</ref><ref>{{Cite web|title=International Laser Ranging Service|url=ftp://edc.dgfi.tum.de/pub/slr/data/npt_crd/}}</ref> and the active stations. Some of the findings of this [[long-term experiment]] are:<ref name="millimeter challenge" />

=== Properties of the Moon ===
* The distance to the Moon can be measured with millimeter precision.<ref name=":1">{{cite journal|last1=Battat|first1=J. B. R.|last2=Murphy|first2=T. W.|last3=Adelberger|first3=E. G.|last4=Gillespie|first4=B.|last5=Hoyle|first5=C. D.|last6=McMillan|first6=R. J.|last7=Michelsen|first7=E. L.|last8=Nordtvedt|first8=K.|last9=Orin|first9=A. E.|last10=Stubbs|first10=C. W.|last11=Swanson|first11=H. E.|display-authors=3|date=January 2009|title=The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO): Two Years of Millimeter-Precision Measurements of the Earth-Moon Range1|journal=Publications of the Astronomical Society of the Pacific|volume=121|issue=875|pages=29–40|bibcode=2009PASP..121...29B|doi=10.1086/596748|jstor=10.1086/596748|doi-access=free}}</ref>
*The Moon is spiraling away from Earth at a rate of {{val|3.8|u=cm|up=year}}.{{r|ApolloLaser}}<ref name="link.springer.com">{{Cite journal|last1=Williams|first1=James G.|last2=Boggs|first2=Dale H.|date=2016|title=Secular tidal changes in lunar orbit and Earth rotation|url=http://link.springer.com/10.1007/s10569-016-9702-3|journal=Celestial Mechanics and Dynamical Astronomy|language=en|volume=126|issue=1|pages=89–129|doi=10.1007/s10569-016-9702-3|bibcode=2016CeMDA.126...89W|s2cid=124256137|issn=0923-2958}}</ref> This rate has been described as anomalously high.<ref>{{Cite journal |last1=Bills |first1=B. G. |last2=Ray |first2=R. D. |year=1999 |title=Lunar Orbital Evolution: A Synthesis of Recent Results |journal=[[Geophysical Research Letters]] |volume=26 |issue=19 |pages=3045–3048 |bibcode=1999GeoRL..26.3045B |doi=10.1029/1999GL008348|doi-access=free }}</ref>
*The fluid core of the Moon was detected from the effects of core/mantle boundary dissipation.<ref>{{Cite journal|last1=Williams|first1=James G.|last2=Boggs|first2=Dale H.|last3=Yoder|first3=Charles F.|last4=Ratcliff|first4=J. Todd|last5=Dickey|first5=Jean O.|date=2001|title=Lunar rotational dissipation in solid body and molten core|journal=Journal of Geophysical Research: Planets|language=en|volume=106|issue=E11|pages=27933–27968|doi=10.1029/2000JE001396|bibcode=2001JGR...10627933W|doi-access=free}}</ref>
*The Moon has free physical [[librations]] that require one or more stimulating mechanisms.<ref>{{Cite journal|last1=Rambaux|first1=N.|last2=Williams|first2=J. G.|date=2011|title=The Moon's physical librations and determination of their free modes|journal=Celestial Mechanics and Dynamical Astronomy|volume=109|issue=1 |pages=85–100|doi=10.1007/s10569-010-9314-2|bibcode=2011CeMDA.109...85R |s2cid=45209988|url=https://hal.archives-ouvertes.fr/hal-00588671/file/PEER_stage2_10.1007%252Fs10569-010-9314-2.pdf}}</ref>  
*Tidal dissipation in the Moon depends on tidal frequency.<ref name="link.springer.com"/>  
* The Moon probably has a liquid core of about 20% of the Moon's radius.{{r|jwjd1}} The radius of the lunar core-mantle boundary is determined as {{val|381|12|u=km}}.{{r|viswanathan2019grl}}
*The polar [[flattening]] of the lunar core-mantle boundary is determined as {{val|2.2|0.6|e=-4}}.{{r|viswanathan2019grl}}
*The free core [[nutation]] of the Moon is determined as {{val|367|100|u=yr}}.<ref name="viswanathan2019grl">{{cite journal|last1=Viswanathan|first1=V.|last2=Rambaux|first2=N.|last3=Fienga|first3=A.|last4=Laskar|first4=J.|last5=Gastineau|first5=M.|date=9 July 2019|title=Observational Constraint on the Radius and Oblateness of the Lunar Core-Mantle Boundary|journal=[[Geophysical Research Letters]]|volume=46|issue=13|pages=7295–7303|arxiv=1903.07205|doi=10.1029/2019GL082677|bibcode=2019GeoRL..46.7295V|s2cid=119508748}}</ref>
*Accurate locations for retroreflectors serve as reference points visible to orbiting spacecraft.<ref>{{Cite journal|last1=Wagner|first1=R. V.|last2=Nelson|first2=D. M.|last3=Plescia|first3=J. B.|last4=Robinson|first4=M. S.|last5=Speyerer|first5=E. J.|last6=Mazarico|first6=E.|date=2017|title=Coordinates of anthropogenic features on the Moon|journal=Icarus|language=en|volume=283|pages=92–103|doi=10.1016/j.icarus.2016.05.011|bibcode=2017Icar..283...92W|issn=0019-1035|doi-access=free}}</ref>

=== Gravitational physics ===
*[[Albert Einstein|Einstein's]] theory of gravity (the [[General relativity|general theory of relativity]]) predicts the [[Orbit of the Moon|Moon's orbit]] to within the accuracy of the laser ranging measurements.{{r|jwjd1}}<ref name=":2" />
* [[Gauge fixing|Gauge freedom]] plays a major role in a correct physical interpretation of the relativistic effects in the Earth-Moon system observed with LLR technique.<ref>{{cite journal |last1=Kopeikin |first1=S. |last2=Xie |first2=Y. |year=2010 |title=Celestial reference frames and the gauge freedom in the post-Newtonian mechanics of the Earth–Moon system |journal=[[Celestial Mechanics and Dynamical Astronomy]] |volume=108 |issue=3 |pages=245–263 |bibcode=2010CeMDA.108..245K |doi=10.1007/s10569-010-9303-5|s2cid=122789819 }}</ref>
* The likelihood of any [[Nordtvedt effect]] (a hypothetical differential acceleration of the Moon and Earth towards the Sun caused by their different degrees of compactness) has been ruled out to high precision,<ref>{{cite journal|last1=Adelberger|first1=E. G.|last2=Heckel|first2=B. R.|last3=Smith|first3=G.|last4=Su|first4=Y.|last5=Swanson|first5=H. E.|year=1990|title=Eötvös experiments, lunar ranging and the strong equivalence principle|journal=[[Nature (journal)|Nature]]|volume=347|issue=6290|pages=261–263|bibcode=1990Natur.347..261A|doi=10.1038/347261a0|s2cid=4286881}}</ref><ref name=":2">{{cite journal|last1=Williams|first1=J. G.|last2=Newhall|first2=X. X.|last3=Dickey|first3=J. O.|year=1996|title=Relativity parameters determined from lunar laser ranging|journal=[[Physical Review D]]|volume=53|issue=12|pages=6730–6739|bibcode=1996PhRvD..53.6730W|doi=10.1103/PhysRevD.53.6730|pmid=10019959}}</ref><ref>{{cite journal|last1=Viswanathan|first1=V|last2=Fienga|first2=A|last3=Minazzoli|first3=O|last4=Bernus|first4=L|last5=Laskar|first5=J|last6=Gastineau|first6=M|date=May 2018|title=The new lunar ephemeris INPOP17a and its application to fundamental physics|journal=Monthly Notices of the Royal Astronomical Society|volume=476|issue=2|pages=1877–1888|arxiv=1710.09167|doi=10.1093/mnras/sty096|doi-access=free|bibcode=2018MNRAS.476.1877V}}</ref> strongly supporting the [[strong equivalence principle]].
* The universal force of [[gravity]] is very stable.  The experiments have constrained the change in [[Isaac Newton|Newton's]] [[gravitational constant]] ''G'' to a factor of {{val|2|7|e=-13}} per year.<ref>{{cite journal|last1=Müller|first1=J.|last2=Biskupek|first2=L.|year=2007|title=Variations of the gravitational constant from lunar laser ranging data|journal=[[Classical and Quantum Gravity]]|volume=24|issue=17|page=4533|doi=10.1088/0264-9381/24/17/017|s2cid=120195732 }}</ref>