Polaris: The North Star
Credit & Copyright: Wally Pacholka


Explanation: Polaris is quite an unusual star. First, Polaris is the nearest bright star to the north spin axis of the Earth. Therefore, as the Earth turns, stars appear to rotate around Polaris, making it the North Star. Since no bright star is near the south spin axis of the Earth, there is currently no South Star. Thousands of years ago, Earth's spin axis pointed in a slightly different direction, and Vega was the North Star. Although Polaris is not the brightest star on the sky, it is easily located because it is nearly aligned with two stars in the cup of the Big Dipper, and is the last star in the handle of the Little Dipper. In the above picture, Polaris is the brightest star on the right, above the fleeting streak of a Perseid meteor. The surface of Polaris slowly pulsates, causing the star to change its brightness by a few percent over the course of a few days. This rare Cepheid variability of Polaris is, oddly enough, itself changing.



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Image: HERE

Image: HERE


Its full astronomical name is "Alpha Draconis"

It was once thought to be the brightest star in the constellation Draco, hence the 'Alpha' designation. The honor really goes to a star named Eltanin, "Gamma Draco". It is believed that Thuban was considerably brighter several thousand years ago.

This star was the pole star at about 2700 BC. The fact that Thuban was the Pole Star at just the time the Egyptians were building pyramids hasn't escaped the archaeologists. Several structures appear to have been set up to align with Thuban during this time.

The Pole Star -- Wichahpi Owanjila, a star that always stands in one place -- was Thuban (Alpha Draconis) around 3000 BC. Around 7500 AD, Alpha Ceiphei will be the pole star, then Deneb, then bright Vega (14000 AD), then it'll swing around to Thuban again. For many centuries there has been and will be no bright star close enogh to where the pole is to serve as pole star; the bright northern stars and constellations then seem to revolve through the night about an empty center.

Thuban, is a mag. 3.7 A type (white).

How to find Thuban in the sky:

Use as pole star

Due to the precession of Earth's rotational axis, Thuban was the naked-eye star closest to the north pole from 3942 BC, when it moved farther north than Theta Boötis, until 1793 BC, when it was superseded by Kappa Draconis. It was closest to the pole in 2787 BC, when it was less than two and a half arc-minutes away from the pole. It remained within one degree of true north for nearly 200 years afterwards, and even 900 years after its closest approach, was just five degrees off the pole. Thuban was considered the pole star until about 1900 BC, when the much brighter Kochab began to approach the pole as well.

Having gradually drifted away from the pole over the last 4,800 years, Thuban is now seen in the night sky at a declination of 64° 20' 45.6", RA 14h 04m 33.58s. After moving nearly 47 degrees off the pole by 10000 AD, Thuban will gradually move back toward the north celestial pole. In 20346 AD, it will again be the pole star, that year reaching a maximum declination of 88° 43' 17.3", RA 19h 08m 54.17s.

The fourth brightest star in the constellation Draco. Thuban used to be the pole star, a distinction it held from 3942 BC to 1793 BC when it was superceded by the faint star Kappa Draconis. In 2787 BC, it lay just 1/180 the width of the full Moon from the pole. Thuban was considered the pole star until about 1900 BC, when the much brighter Kochab began to approach the pole as well.

Although Thuban lies in the Dragon's tail, its name comes from an Arabic phrase that means "the Serpent's head." Thuban belongs to the fairly rare class of giant A stars. It has a faint unseen companion in a 51.4-day orbit that may be a red dwarf or a low-mass white dwarf.


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