In other words, it takes 26, years for the axis to trace out the cone one complete time. So now you can see why Polaris will not always be aligned with the north spin axis of the Earth - because that axis is slowly changing the direction in which it points! Right now, the Earth's rotation axis happens to be pointing almost exactly at Polaris.
But in the year B. Don't feel bad for Polaris, however, because in 26, more years it will once again be the Pole Star! By the way, there is not currently a star in the direction of the southern hemisphere spin axis. So we do not now have a "South Star". Thirdly, Polaris is not exactly lined up with earth's axis of rotation. There is very low probability that any star would end up exactly lined up with earth's axis. Polaris lies at a viewing angle that is 0.
Because the North Star does not lie exactly on earth's rotation axis, it actually arcs through the sky every night. The arc is just so small that humans can't see it. Furthermore, earth's rotation axis is not completely fixed.
Because earth is not perfectly spherical but bulges at the equator, the sun's gravitational effects on the earth are not completely symmetrical.
This non-symmetry creates a very small and very slow twist on the earth that is turning earth's rotation axis away from Polaris. Not only is it a curiosity, but this variation in position depending on the place of observation makes it useful.
The North Star was one of the best: just by looking at it sailors could deduce the four cardinal points like an infallible compass in the sky and by calculating its height in the sky one could know the variation in latitude with respect to the port of origin and whether it was to the north or the south.
Especially useful in those times was an instrument known as an astrolabe , easy to build, which for centuries helped sailors to know their position in the sea.
Another equally useful instrument is the nocturnal also called a horologium nocturnum or nocturlabe , which uses the position of Polaris compared to the star Beta Ursae Minoris formerly named Kochab to give the solar time at night; it provides the same information as a sundial, but can be used at night. All this is very useful until one passes the equator, when the North Star is no longer visible, and that is why in the southern hemisphere both the astrolabe and the nocturnal cease to function.
Unfortunately, over the South Pole there is no bright star as well aligned as Polaris, which is just bad luck. But it is always possible to locate the South Celestial Pole if we know how to identify the Southern Cross , which is very close.
During the night, this constellation makes a small turn around the South Celestial Pole, which in principle can be a bit confusing… but there is a trick to never lose the South, if we join the Southern Cross with the Magellanic Clouds : a tribute to the importance of astronomy for navigation, and in particular for one of the greatest seafarers of all time, the Portuguese explorer Ferdinand Magellan.
Click Enter. Login Profile. Es En. Economy Humanities Science Technology. Multimedia OpenMind books Authors. One can observe a similar behavior in spinning gyroscopes. As the gyroscope rotates, the top repeatedly describes a circle due to precessional wobbling.
Our planet's wobble is much longer, of course, so that even over a human lifetime, its effects are subtle. Because of precession, different stars will serve as north stars and the constellations arrayed along the ecliptic zodiac will gradually change positions. Their move about one degree every 73 years. Polaris will remain the North Star throughout the rest of our lives and for a few centuries later.
Throughout the past few centuries, Polaris has served as a North Star marker for navigators, escaping slaves and other explorers.
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