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Use the Big Dipper to find the Little Dipper

A photo showing the Big and Little Dippers.
View at EarthSky Community Photos. | Cecille Kennedy in Depoe Bay, Oregon, caught the Big Dipper and the Little Dipper on June 9, 2021. She wrote: “The 2 stars that form the side of the Big Dipper, opposite the handle, point to Polaris, the North Star. Polaris is the last star in the handle of the Little Dipper. Trivia: Alaska’s state flag features The Big Dipper and Polaris the North Star. Benny Benson, a 13-year-old 7th grader from an orphanage in Seward, Alaska, created the flag design.” Thank you, Cecille!

The Big Dipper – also called the Plough – is easy. You’ll find it high in the north on April evenings. Notice it has two parts: a handle and a bowl. The two outer stars in the Big Dipper’s bowl are sometimes called the pointers. They point toward Polaris, the North Star. Polaris is at the end of the Little Dipper’s handle.

Many people say they can spot the Big Dipper easily, but not the Little Dipper. The Little Dipper’s stars are fainter, and its dipper pattern is less dipper-like than its larger neighbor. The best way to find the Little Dipper is to use the Big Dipper as a guide.

Still can’t see the Little Dipper? Try looking in a darker sky.

The Big and Little Dippers aren’t constellations. They’re asterisms, or noticeable patterns – in this case within a single constellation – on the sky’s dome. Both the Big and the Little Dipper belong to the constellation Ursa Major, the Great Bear.

Diagram of Big and Little Dippers with arrow from pointer stars to Polaris.
Kochab and Pherkad are the 2 outermost stars in the bowl of the Little Dipper. They used to be pole stars!

Now about the star Polaris. It’s special because Earth’s northern axis points (nearly) to its location in the sky. It’s the star around which the entire northern sky appears to turn.

Polaris is less than a degree away from the true north celestial pole on the sky’s dome now. It’ll be closest to true north – less than half a degree away – in the year 2102. The change in the location of the celestial pole with respect to Polaris is due to a motion of Earth called precession. This motion causes Earth’s axis to trace out a circle among the stars every 26,000 years.

Polaris wasn’t always the North Star. Thousands of years ago, it was an ordinary star in the northern sky, known to the Greeks by the name Phoenice. Slowly, over eons of time, the north celestial pole moved closer to Polaris.

Other ordinary stars in the northern sky have also had the honor of being the pole star, aka the north star. That includes Kochab and Pherkad, the two outermost stars in the bowl of the Little Dipper (see chart above).

Kochab and Pherkad served as twin pole stars from about 1500 B.C. to about 500 B.C.

They’re still sometimes called the Guardians of the Pole.

Kochab is located about 126 light-years away. Pherkad is more distant, at about 480 light-years by some estimates. Meanwhile, Polaris is a bit more than 400 light-years away.

Sky photo with Big Dipper outlined and arrow to North Star.
View larger. | It doesn’t matter how the Big Dipper is oriented in your sky. If you can see it, the 2 outer stars in its bowl will point to Polaris. In this shot, Tom Wildoner caught the Big Dipper and Polaris at around 3:30 a.m. in July 2013. Thanks, Tom!
Big Dipper with red line to Polaris next to horizon from southerly latitude.
View larger. | Here’s a differently oriented Dipper, with its 2 outer stars still pointing to Polaris, the North Star. Photo by EarthSky Facebook friend Abhijit Juvekar Thank you, Abhijit!

Bottom line: The Big Dipper is usually pretty easy to find, but the Little Dipper is less easy. This post tells you how to use the Big Dipper to find Polaris and the Little Dipper. It also introduces you to two former pole stars, Kochab and Pherkad.

Thuban: Past North Star

Star Errai: Future North Star

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Posted 
April 8, 2021
 in 
Tonight

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