Where's the Big Dipper?


Last updated 2/15/2024 at 11:27am

The Big Dipper is a star grouping, not a constellation as many mistakenly believe.

One question I'm asked frequently during my January night sky tours is, "Where the Big Dipper?" Look for it after dark during January and you, too, will discover that it's nowhere to be found.

The Big Dipper is one of the most famous star groupings and one that nearly all stargazers instantly recognize. Notice I didn't call it a "constellation," because it's not a constellation. It's an "asterism," a group of stars that seems to look like something familiar.

If you've followed my column for a while, you've learned that constellations are simply areas of the sky designated by ancient sky watchers to represent objects, animals and people. But try to see these figures and you'll be in for a disappointment.

The Dipper's familiar shape is formed by tracing the seven brightest stars of the constellation Ursa Major, the Great Bear, into a bowl with a bent handle. We in North America call it the Big Dipper, but in the U.K., it's known as the "Plough," in Germany as the "Great Wagon" and elsewhere by other creative names.

So back to the original question ... where the heck is it? Unfortunately, it's below the horizon at this time of year. Let me explain.

Our Earth rotates once about every 24 hours and, as it spins from west to east, the entire sky appears to turn in the opposite direction. Since our rotational axis aims roughly in the direction of Polaris, this star never seems to move. It's as if the North Star forms the hub of a great celestial wheel with all the stars spinning counterclockwise around it. And that is why the North Star is so important.

Look toward the northern sky on January nights and you'll see the North Star with Cassiopeia high above it – almost overhead from many places. Cassiopeia represents an ancient Ethiopian queen, but you'll do much better if you search for a zigzag of five stars that, right now, appears like the letter "M."

The Big Dipper lies on the opposite side of the North Star from Cassiopeia. And since both these asterisms turn about Polaris as if on a fixed wheel, the position of one will tell you the location of the other.

If you're willing to wait a few hours, you'll see Cassiopeia gradually swing toward the northwestern side of Polaris while the Big Dipper begins to rise from out of the northeastern horizon. And if you wait patiently until early morning hours – or set your alarm to go out before dawn – you'll notice that Cassiopeia appears quite low in the northwest while the Dipper shines brightly high in the northeast.

In other words, when Cassiopeia is high in the sky (as it is during early evenings in January), the Big Dipper is very low. And vice versa.

So when's the best time to see the Big Dipper during the early evening hours? That comes in late spring and summer when it appears nearly overhead. This depends not only on our planet's rotation but also on our annual revolution about the sun.

And where will Cassiopeia be at that time? You now know exactly where to look!

Visit Dennis Mammana at dennismammana.com.