Editing Axial precession (section)

==Changing pole stars==
[[Image:Precession N.gif|right|thumb|upright=1.2|Precession of Earth's axis around the north ecliptical pole]]
A consequence of the precession is a changing [[pole star]]. Currently [[Polaris]] is extremely well suited to mark the position of the north celestial pole, as Polaris is a moderately bright star with a visual [[apparent magnitude|magnitude]] of 2.1 (variable), and is located about one degree from the pole, with no stars of similar brightness too close.<ref name="hipparcos">{{cite web | url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=11739 | title=HIP 11767 | work=Hipparcos, the New Reduction | author=van Leeuwen, F. |year=2007 | access-date=1 March 2011}}</ref>
[[Image:Precession S.gif|left|thumb|upright=1.2|Precession of Earth's axis around the south ecliptical pole]]

The previous pole star was [[Beta Ursae Minoris|Kochab]] (Beta Ursae Minoris, β UMi, β Ursae Minoris), the brightest star in the bowl of the "Little Dipper", located 16 degrees from Polaris. It held that role from 1500 BC to AD 500.<ref name=StardateKochab>{{cite news|last1=Benningfield|first1=Damond|title=Kochab|url=http://stardate.org/radio/program/2015-06-14|access-date=14 June 2015|work=Stardate Magazine|publisher=University of Texas McDonald Observatory|date=14 June 2015}}</ref> It was not quite as accurate in its day as Polaris is today.<ref name=StardateKochab/> Today, Kochab and its neighbor Pherkad are referred to as the "Guardians of the Pole" (meaning Polaris).<ref name=StardateKochab/>

On the other hand, [[Thuban]] in the [[constellation]] [[Draco (constellation)|Draco]], which was the pole star in 3000 BC, is much less conspicuous at magnitude 3.67 (one-fifth as bright as Polaris); today it is invisible in [[Light pollution|light-polluted]] urban skies.

When Polaris becomes the north star again around 27,800, it will then be farther away from the pole than it is now due to its [[proper motion]], while in 23,600 BC it came closer to the pole.

It is more difficult to find the south celestial pole in the sky at this moment, as that area is a particularly bland portion of the sky. The nominal south pole star is [[Sigma Octantis]], which with magnitude 5.5 is barely visible to the naked eye even under ideal conditions. That will change from the 80th to the 90th centuries, however, when the south celestial pole travels through the [[False Cross]].

This situation also is seen on a star map. The orientation of the south pole is moving toward the [[Crux|Southern Cross]] constellation. For the last 2,000 years or so, the Southern Cross has pointed to the south celestial pole. As a consequence, the constellation is difficult to view from subtropical northern latitudes, unlike in the time of the [[ancient Greeks]].  The Southern Cross can be viewed from as far north as [[Miami]] (about 25°&nbsp;N), but only during the winter/early spring.{{clear|right}}