Editing Celestial pole (section)

==Finding the south celestial pole==
[[File:South Celestial Pole.ogv|right|thumb|400px|A series of shots show the rotation of Earth's axis relative to the south celestial pole. The [[Magellanic Clouds]] and the [[Southern Cross]] are clearly visible. Near the end of the video, the Moon rises and illuminates the scene.]]
[[File:Swirling Star Trails Over Yepun.jpg|thumb|The south celestial pole over the [[Very Large Telescope]]<ref>{{cite web|title=Swirling Star Trails Over Yepun|url=https://www.eso.org/public/images/potw1301a/|work=Picture of the Week|publisher=ESO|access-date=11 January 2013}}</ref> ]]
[[File:South celestial pole.png|thumb|South celestial pole]]

The south celestial pole is visible only from the [[Southern Hemisphere]]. It lies in the dim [[constellation]] [[Octans]], the Octant. [[Sigma Octantis]] is identified as the south pole star, more than one degree away from the pole, but with a magnitude of 5.5 it is barely visible on a clear night.

===Method one: The Southern Cross===

The south celestial pole can be located from the [[Crux|Southern Cross]] (Crux) and its two "pointer" stars [[Alpha Centauri|α Centauri]] and [[Beta Centauri|β Centauri]]. Draw an imaginary line from [[Gamma Crucis|γ Crucis]] to [[Alpha Crucis|α Crucis]]&mdash;the two stars at the extreme ends of the long axis of the cross&mdash;and follow this line through the sky. Either go four-and-a-half times the distance of the long axis in the direction the narrow end of the cross points, or join the two pointer stars with a line, divide this line in half, then at right angles draw another imaginary line through the sky until it meets the line from the Southern Cross. This point is 5 or 6 degrees from the south celestial pole. Very few bright stars of importance lie between Crux and the pole itself, although the constellation [[Musca]] is fairly easily recognised immediately beneath Crux.

===Method two: Canopus and Achernar===

The second method uses [[Canopus]] (the second-brightest star in the sky) and [[Achernar]]. Make a large [[equilateral triangle]] using these stars for two of the corners. But where should the third corner go? It could be on either side of the line connecting Achernar and Canopus, and the wrong side will not lead to the pole. To find the correct side, imagine that Archernar and Canopus are both points on the circumference of a circle. The third corner of the equilateral triangle will also be on this circle. The corner should be placed clockwise from Achernar and anticlockwise from Canopus. The third imaginary corner will be the south celestial pole. If the opposite is done, the point will land in the middle of [[Eridanus (constellation)|Eridanus]], which isn't at the pole. If Canopus has not yet risen, the second-magnitude [[Alpha Pavonis]] can also be used to form the triangle with Achernar and the pole. In this case, go anticlockwise from Achernar instead of clockwise, form the triangle with Canopus, and the third point, the pole, will reveal itself. The wrong way will lead to Aquarius, which is very far away from the celestial pole.

===Method three: The Magellanic Clouds===

The third method is best for moonless and clear nights, as it uses [[Magellanic Clouds|two faint "clouds"]] in the [[Southern Celestial Hemisphere|Southern Sky]]. These are marked in astronomy books as the [[Large Magellanic Cloud|Large]] and [[Small Magellanic Cloud]]s (the LMC and the SMC). These "clouds" are actually [[dwarf galaxy|dwarf galaxies]] near the [[Milky Way]]. Make an equilateral triangle, the third point of which is the south celestial pole. Like before, the SMC, LMC, and the pole will all be points on an equilateral triangle on an imaginary circle. The pole should be placed clockwise from the SMC and anticlockwise from the LMC. Going in the wrong direction will land you in the constellation of [[Horologium (constellation)|Horologium]] instead.

===Method four: Sirius and Canopus===

A line from [[Sirius]], the brightest star in the sky, through Canopus, the second-brightest, continued for the same distance lands within a couple of degrees of the pole. In other words, Canopus is halfway between Sirius and the pole.