Polaris - 10 Fascinating Facts

Polaris - 10 Fascinating Facts
A view of the entire sky as seen from Quito, Ecuador on the evening May 7, 2014. The celestial equator crosses directly overhead while each pole star lies 90 degrees away on opposite horizons. [Credit: Astrobob, using Stellarium]

1. If you can find Polaris, you know which direction is north.
If you stand facing Polaris and stretch your arms out to your sides, your right hand will point east and your left hand will point west.

2. Polaris is easy to find.
You can locate Polaris from the Big Dipper (called “the Plough” in Britain). This is the one star pattern almost everyone knows. The two stars of the bowl which are farthest from the handle are called Merak and Dubhe. If you follow their line, as shown here, they point to Polaris. This is particularly useful at latitude 41 degrees and above, because the Big Dipper is always above the horizon there. It can sometimes be seen all the way down to just south of the Equator.

3. Polaris is not the brightest star in the sky.
Although it's a common belief that Polaris is exceptionally bright, the importance of Polaris is its position. Yet it's a second magnitude star, so it's still fairly easy to see, and it is among the top fifty brightest stars we see. (The dimmer a star appears. the higher its magnitude number. The bright star Sirius actually has a negative magnitude.)

4. Polaris indicates north because it just happens to be in line with Earth's north pole.
Imagine the north pole of Earth's axis pointing into the sky. It points to within one degree of Polaris. If you were outside trying to orient yourself, this would point you in the right direction, though navigators have to correct for the fact that it's not exact.

5. If you look at the stars more than once over several hours, you'll see the stars seeming to move during the night – except for Polaris.
You can capture this movement by pointing a camera at the sky and leaving the shutter open. As the Earth turns, the light from the stars forms star trails. In this picture taken by P-M Hedén in Sweden, you can see Polaris in the center of the circles. Since it's in line with the Earth's axis of rotation, not only does it seem to stay in the same place, all the other stars seem to revolve around it.

6. Polaris hasn't always been the pole star.
Polaris has been used for navigation since the fifth century, but when the Egyptians built the pyramids, Thuban (in the constellation Draco) was nearest to the north celestial pole. Vega (in the constellation Lyra) will be the pole star twelve thousand years from now. This is because of what's called precession. Earth's axis has a little wobble in it, and over a period of 26,000 years the axis points to different areas of the sky.

7. Polaris has been known throughout most of the northern hemisphere for thousands of years and it has names in many languages.
For astronomers, Polaris is Alpha Ursae Minoris, i.e., the alpha star of Ursa Minor (Little Bear). In English it's commonly called the North Star or the Pole Star, though Lodestar or Guiding Star are other older names. Cynosura was an ancient Greek name from the time when the constellation represented a dog. The name means “the dog's tail”.

8. Polaris is not a single star, but a triple star system.
The main star (Polaris A) is is a supergiant six times the mass of the Sun. It's also a variable star of the Cepheid type which, based on Henrietta Leavitt's work on Cepheid variables, can be used to measure galactic distances. Polaris A has a sunlike companion (Polaris B) which orbits at a great enough distance that it can be distinguished with good binoculars. William Herschel discovered it in 1780. A second companion (Polaris Ab) is so close to Polaris A that it was only discovered because of its spectrum.

9. In nineteenth century America, before the end of the Civil War, escaped slaves “followed the drinking gourd” to freedom in the north.
The “drinking gourd” was the Big Dipper which lets you locate Polaris. Along with instructions passed on by anti-slavery activists, the pole star helped them find their way to sympathizers in the northern states and perhaps on to Canada.

10. The southern hemisphere doesn't have an equivalent of Polaris.
Sigma Octantis (in the constellation Octans) is sometimes named as the southern pole star. However, although it's fairly close to the pole, it's very faint, nearly sixth magnitude. Viewing conditions would have to be quite good in order to locate it. For navigation in the southern hemisphere, the Southern Cross (constellation Crux) is used.



You Should Also Read:
Octans - the Octant
Naming Stars
Henrietta Swan Leavitt

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