Orbit of the Moon: Difference between revisions

→‎Path of Earth and Moon around Sun: remove seemingly pointless sentence about "turning off" the Sun's gravity; it made sense in context when it was added (rev. 92048191, 19:11, 4 December 2006), but that context has gradually eroded away
m (Reverting possible vandalism by 165.24.201.194 to version by Fyrael. False positive? Report it. Thanks, ClueBot NG. (1595960) (Bot))
(→‎Path of Earth and Moon around Sun: remove seemingly pointless sentence about "turning off" the Sun's gravity; it made sense in context when it was added (rev. 92048191, 19:11, 4 December 2006), but that context has gradually eroded away)
Considering the Earth–Moon system as a binary planet, their mutual centre of gravity is within the Earth, about 4624&nbsp;km from its centre or 72.6% of its radius. This centre of gravity remains in-line towards the Moon as the Earth completes its diurnal rotation. It is this mutual centre of gravity that defines the path of the Earth–Moon system in solar orbit. Consequently the Earth's centre veers inside and outside the orbital path during each synodic month as the Moon moves in the opposite direction.<ref name="convex" />
 
Unlike most moons in the Solar System, the trajectory of the Moon around the Sun is very similar to that of Earth. The Sun's gravitational effect on the Moon is over twice as great as the Earth's on the Moon; consequently, the Moon's trajectory is always convex<ref name = "convex"/><ref>[http://www.mathpages.com/home/kmath405/kmath405.htm The Moon Always Veers Toward the Sun] at MathPages</ref> (as seen when looking Sunward at the entire Moon/Earth/Sun system from a great distance outside the Earth/Moon solar orbit), and is nowhere concave (from the same perspective) or looped.<ref name=shapes3>The reference by H L Vacher (2001)(details separately cited in this list) describes this as 'convex outward', while older references such as "[http://adsabs.harvard.edu/full/1912JRASC...6..117T ''The Moon's Orbit Around the Sun'', Turner, A. B. Journal of the Royal Astronomical Society of Canada, Vol. 6, p.117, 1912JRASC...6..117T]"; and "[http://books.google.com/books?id=QKvx4pm0QJgC&pg=PA85&lpg=PA85&dq=moon+orbit+sun+concave&source=bl&ots=Vzj7IOLHYf&sig=z_BGTd0v3gabNimk4rVKgLzxl7c&hl=en&ei=JN_JSaTXM8PR-AaXqdjoBw&sa=X&oi=book_result&resnum=6&ct=result H Godfray, ''Elementary Treatise on the Lunar Theory'']" describe the same geometry by the words ''concave to the sun''.</ref><ref name = "convex">{{cite web |last=Aslaksen |first=Helmer |year=2010 |url=http://www.math.nus.edu.sg/aslaksen/teaching/convex.html| title=The Orbit of the Moon around the Sun is Convex!| accessdate=2006-04-21}}</ref><ref>{{cite journal| url=http://www.nagt.org/files/nagt/jge/columns/CG18-v49n5p470.pdf| format=PDF| accessdate=2006-04-21| journal=Journal of Geoscience Education| issue=5| pages=470–479| month=November| year=2001| title=Computational Geology 18 – Definition and the Concept of Set| first=H.L.| last=Vacher| volume=49}}</ref> If the gravitational attraction of the Sun could be "turned off" while maintaining the Earth–Moon gravitational attraction, the Moon would continue to orbit the Earth once every [[sidereal month]].
 
==See also==