Last week we explored the Big Dipper, so this week we take a look at the Little Dipper, also known as the Little Bear or Ursa Minor. In trying to find it -- high overhead at night now -- you'll get an idea how much light pollution affects your local sky.

Seven relatively faint stars make up the Little Dipper. The four faintest of these can be blotted out with very little moonlight or street lighting.

Polaris, the North Star, lies at the end of the handle. As noted last week, the best way to find your way to Polaris is to use the so-called "Pointer" stars in the bowl of the Big Dipper, Dubhe and Merak. Just draw a line, between these two stars and prolong it about 5 times, and you eventually will arrive in the vicinity of Polaris.

At the North Pole, you would find Polaris directly overhead. From New York City the North Star is almost halfway from the horizon to an imaginary point directly overhead, called the zenith. At the equator, Polaris would appear to sit right on the horizon. So if you travel to the north, the North Star climbs progressively higher the farther north you go. When you head south, the star drops lower and ultimately disappears once you cross the equator and head into the Southern Hemisphere.

In addition to Polaris, the two stars at the front of the Little Dipper's bowl are readily seen. These two are often referred to as the "Guardians of the Pole" because they appear to march around Polaris like sentries. Columbus mentioned these stars in the log of his famous journey across the ocean, and many other navigators have found them useful in measuring the hour of the night and their place upon the sea.

The brightest Guardian is Kochab, a second magnitude star with an orange hue. The other Guardian goes by an old Arabian name, Pherkad -- the "Dim One of the Two Calves." Pherkad is indeed dimmer than Kochab, shining at third magnitude. The two other stars that complete the pattern of the bowl of the Little Dipper are of fourth and fifth magnitude, pushing the limits of what most people can see even with relatively minor light pollution.

Thus, the bowl of the Little Dipper, which is visible at any hour on any night of the year from most localities in the Northern Hemisphere, can serve as an indicator for rating just how dark and clear your night sky really is. If, for example, you can readily see all four stars in the bowl, you've got yourself a good-to-excellent sky.

Unfortunately, thanks to the spread of light pollution in recent years, only the Guardians are usually visible from most city and suburban sites, meaning the quality of the sky would rank fair-to-poor.

Interestingly, the Big and Little dippers are arranged so that when one is upright, the other is upside down. In addition, their handles appear to extend in opposite directions. Of course, the Big Dipper is by far the brighter of the two, appearing as a long-handled pan, while the Little Dipper resembles a dim ladle.

Finally, there is a popular misconception that the North Star is the brightest star in the sky. Yet it actually ranks only 49th in brightness. Polaris remains in very nearly the same spot in the sky year-round while the other stars circle around it. Only the apparent width of about 1 full Moons separates Polaris from the pivot point directly in the north around which the stars go daily.

However, on account of the wobble of the Earth's axis (called precession), the celestial pole shifts as the centuries go by. Polaris is actually still drawing closer to the pole and on March 24, 2100, it will be as close to it as it ever will come, just 27.15 arc-minutes or slightly less than the Moon's apparent diameter.

Since it takes just less than 26,000 years for the Earth's axis to complete a single wobble, different stars have become the North Star at different times. The brightest Guardian, Kochab, was the North Star at the time of Plato, around 400 BC.

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