The farther a star is from the pole, the larger the circle it travels around the sky. Some stars travel a great distance over the course of the night.
Polaris is different. Because it's so close to the celestial pole, it traces out a very small circle over 24 hours. So Polaris always stays in roughly the same place in the sky, and therefore it's a reliable way to find the direction of north.
It would appear directly overhead if you stood at the north pole, but farther south, it indicated the direction of north. On this astronomers' scale, smaller numbers represent brighter objects, with the brightest stars and planets in the night sky at around magnitude zero or even negative magnitudes. The North Star it is a "pulsing" star, a Cepheid variable , which appears to vary in brightness ever so slightly — only one tenth of a magnitude — over a time frame of just under four days.
If you have a small telescope and train it on Polaris, you just might notice a tiny companion star called Polaris B shining at 9th magnitude with a pale bluish tint. This companion was first sighted by Sir William Herschel in just a year later, Herschel would discover the planet Uranus. Astronomers believe that the two stars — A and B — are separated by about 2, astronomical units — one astronomical unit a. The orbital period of the two stars may number in the many thousands of years.
In , by studying the spectrum of Polaris, a third companion star Polaris C was discovered. This one, a white dwarf, lies only Its extreme closeness to the far more brilliant Polaris A explains why it went unseen for so long. Exactly where you see Polaris in your northern sky depends on your latitude. From New York it stands 41 degrees above the northern horizon, which also corresponds to the latitude of New York.
Since 10 degrees is roughly equal to your clenched fist held at arm's length, from New York Polaris would appear to stand about "four fists" above the northern horizon.
At the North Pole, you would find it overhead. At the equator, Polaris would appear to sit right on the horizon. The Earth spins on its "axis". This axis is an imaginary line running through the Earth. If you were to be high above the Earth, looking straight down along the axis, all the points on Earth would appear to move in circles around the axis. If you followed this axis out into space from the northern hemisphere on Earth, it would point toward a particular star in the sky.
We call that star the "North Star" since it sits in the direction that the spin axis from the northern hemisphere of Earth points. At present, the star known as Polaris is the North Star. To understand that, we need to look at how the Earth spins on its axis. For the best user experience, enable javascript in your browser.
Jump to main content. It will, however, eventually become our North Star in about 13, years. The North Celestial Pole NCP is restless and over the course of 26, years will describe a 47 degree arc through the sky. Consequently, the NCP will align itself toward various stars over time. Precessional wobbling causes this NCP displacement. The influence of the Sun, Moon and, to a lesser extent, planets, cause Earth's pole to precess over a long time period.
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