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[[Mercury]] is the smallest planet in the [[Solar System]], and it is the closest to the [[Sun]].  It orbits the [[Sun]] in 88 (Earth) days. It rotates on its axis every 58.6 days,<ref>"The theory that Mercury is in [[synchronous rotation]] with its orbital motion was shattered in 1965. Astronomers Gordon Pettengill and Rolf Dyce used a radio telescope to make radar observations of Mercury’s spin rate. They found that Mercury’s rotation period is only 58.6 Earth days, not the 88 days accepted for nearly a century." [http://btc.montana.edu/messenger/elusive_planet/modern_times.htm]</ref> which is 3 rotations for every two orbits (called "3:2 resonance").  It can be seen from [[Earth]] only at sunrise and sunset.<ref name="spacemag">[http://www.space.com/spacewatch/mercury_view_030404.html Seeing Mercury at sunset], April 2003</ref>

[[Mercury]] is the smallest planet in the [[Solar System]], and it is the closest to the [[Sun]].  It orbits the [[Sun]] in 88 (Earth) days. It rotates on its axis every 58.6 days,<ref>"The theory that Mercury is in [[synchronous rotation]] with its orbital motion was shattered in 1965. Astronomers Gordon Pettengill and Rolf Dyce used a radio telescope to make radar observations of Mercury’s spin rate. They found that Mercury’s rotation period is only 58.6 Earth days, not the 88 days accepted for nearly a century." [http://btc.montana.edu/messenger/elusive_planet/modern_times.htm]</ref> which is 3 rotations for every two orbits (called "3:2 resonance").  It can be seen from [[Earth]] only at sunrise and sunset.<ref name="spacemag">[http://www.space.com/spacewatch/mercury_view_030404.html Seeing Mercury at sunset], April 2003</ref>

{{quotebox|Mercury has a very elliptical orbit. At its farthest distance from the Sun, it is nearly 50% farther than at its nearest distance to the Sun. <ref> [http://astroprofspage.com/archives/139 ] </ref> }}

Mercury is one of the five brightest planets.

The [[precession]] of Mercury's eccentric orbit was detectable to 19th century astronomers.<ref name=Wudka>Wudka, Jose. "[http://phyun5.ucr.edu/~wudka/Physics7/Notes_www/node98.html Precession of the perihelion of Mercury]." September 24, 1998. Accessed April 17, 2008.</ref><ref name=Britannica>"[http://www.britannica.com/eb/article-241978/Mercury Mercury: Mercury in tests of relativity]."  In "Mercury," ''Encyclopædia Britannica'', 2008. Encyclopædia Britannica Online. 17 April 2008</ref>

== Ancient History ==

 

As with the other planets of the solar system, it was named after after Roman mythology, in this case the messenger god Mercury who is known as [[Hermes]] in Greek.

 

Mercury is one of the five brightest planets, and has been known since ancient times.

{{quotebox|In the pre-Christian era, this planet actually had two names, as it was not realized it could alternately appear on one side of the Sun and then the other. Mercury was called Mercury when in the evening sky, but was known as Apollo when it appeared in the morning. It is said that [[Pythagoras]], about the fifth century B.C., pointed out that they were one and the same.<ref name="spacemag"/> }}

In the pre-Christian era, this planet actually had two names, as it was not realized it could alternately appear on one side of the Sun and then the other. Mercury was called Mercury when in the evening sky, but was known as Apollo when it appeared in the morning. It is said that [[Pythagoras]], about the fifth century B.C., pointed out that they were one and the same.<ref name="spacemag"/>  

== Composition ==

== Composition ==

== Orbital oddities ==

== Orbital oddities ==

It was the study of this planet's orbit that [[Albert Einstein]] used to help confirm the [[General Theory of Relativity]].<ref>Testing general relativity [http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31277 European Space Agency] Accessed July 16 2007</ref><ref>Albert Einstein [http://www.phy.hr/ Fizički odsjek] Accessed July 16 2007</ref> Specifically, Mercury's [[apsis|perihelion]] precesses by 5600 arc-seconds per century, which is 43 arc-seconds per century more than [[Sir Isaac Newton|Newtonian]] physics alone would predict from the respective masses of Mercury, the Sun, and the other planets. Astronomers of the period hypthesized either an [[Asteroid Belt|asteroid belt]] or another planet (which they named [[Vulcan (planet)|Vulcan]]) inside Mercury's orbit. Einstein's second-order correction to Mercury's orbit accounted exactly for the 43 arc-seconds of precession and obviated the need to look for any unseen asteroids or innermost planet.<ref name=Hartnett>Hartnett, John. ''Starlight, Time, and the New Physics''. Creation Book Publishers, 2007, pp. 34-36. ISBN 9780949906687.</ref><ref name=Wudka/><ref name=Britannica/>

It was the study of this planet's orbit that [[Albert Einstein]] used to help confirm the [[General Theory of Relativity]].<ref>Testing general relativity [http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31277 European Space Agency] Accessed July 16 2007</ref><ref>Albert Einstein [http://www.phy.hr/ Fizički odsjek] Accessed July 16 2007</ref> Specifically, Mercury's [[apsis|perihelion]] precesses by 5600 arc-seconds per century, which is 43 arc-seconds per century more than [[Sir Isaac Newton|Newtonian]] physics alone would predict from the respective masses of Mercury, the Sun, and the other planets. Astronomers of the period hypthesized either an [[Asteroid Belt|asteroid belt]] or another planet (which they named [[Vulcan (planet)|Vulcan]]) inside Mercury's orbit. Einstein's second-order correction to Mercury's orbit accounted exactly for the 43 arc-seconds of precession and obviated the need to look for any unseen asteroids or innermost planet.<ref name=Hartnett>Hartnett, John. ''Starlight, Time, and the New Physics''. Creation Book Publishers, 2007, pp. 34-36. ISBN 9780949906687.</ref><ref name=Wudka/><ref name=Britannica/>