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== The first dark matter ==

== The first dark matter ==

: ''Main Article: [[Vulcan (planet)|Vulcan]]''

: ''Main Article: [[Vulcan (planet)|Vulcan]]''

The first recorded instance of the invocation of anything similar to dark matter was the hypothesis of a [[planet]] named [[Vulcan (planet)|Vulcan]] in the mid-1850s. This planet was supposed to be inside the orbit of [[Mercury]] and yet was never directly observed from [[Earth]], for reasons that no astronomer ever explained. Astronomers inferred the existence of this planet because Mercury precessed in its orbit around the Sun by 43 arc-seconds per century faster than its own mass, and that of the [[sun]], as Newtonian physics would predict. Many apparently observed transits of unidentified objects across the sun were thought to be this undiscovered planet.

The first recorded instance of the invocation of anything similar to dark matter was the hypothesis of a [[planet]] named [[Vulcan (planet)|Vulcan]] in the mid-1850s. This planet was supposed to be inside the orbit of [[Mercury]] and yet was never directly observed from [[Earth]], for reasons that no astronomer ever explained. Astronomers inferred the existence of this planet because Mercury precessed in its orbit around the Sun by 43 arc-seconds per century faster than expected by Newtonian physics. Many apparently observed transits of unidentified objects across the sun were thought to be this undiscovered planet.

Then in 1915, [[Albert Einstein]] solved the problem. He showed that Mercury, at [[apsis|perihelion]], passes close enough to the Sun for [[General Relativity]] to require a second-order correction. He published the correction and accounted exactly for the precession in the orbit of Mercury, without the need for any planet, [[asteroid]] belt, or other object or objects inside that orbit.<ref name=Hartnett>Hartnett, John. ''[[Starlight, Time and the New Physics]]''. Creation Book Publishers, 2007. ISBN 9780949906687.</ref>

Then in 1915, [[Albert Einstein]] solved the problem. He showed that Mercury, at [[apsis|perihelion]], passes close enough to the Sun for [[General Relativity]] to require a second-order correction. He published the correction and accounted exactly for the precession in the orbit of Mercury, without the need for any planet, [[asteroid]] belt, or other object or objects inside that orbit.<ref name=Hartnett>Hartnett, John. ''[[Starlight, Time and the New Physics]]''. Creation Book Publishers, 2007. ISBN 9780949906687.</ref>