A star show for Saipan’s night owls

I’ve already blown my holiday budget for the year. So for Thanksgiving I thanked my lucky stars for, well, for the stars themselves. After all, they’re always putting on a show. Everyone can afford to see it. Yes, even I can.

One of the sky’s most famous sights is the Big Dipper. It’s playing coy this time of year, but that’s the fun: It’s only revealing itself to night owls. So, for the night owls out there, including the hardy folks who are working the graveyard shift while everyone else enjoys the holidays, let’s take a look at the Big Dipper.

It’s going to be a quick look, merely hitting the highlights.

I’ll nominate myself for the worst description of the year award. Here’s my summary of the Big Dipper: The Big Dipper looks like, well, a big dipper.

This cosmic paint-by numbers picture is defined by seven stars, three of which form the handle, and four of which form the bowl. Whenever you see the Big Dipper, you’ll see it in the northern part of the sky.

And this brings us to a star that’s the Big Dipper’s best friend. I refer to the north star, also known as Polaris. Polaris always stands at true north, and, from Saipan, Polaris is always fixed 15 degrees over the horizon.

With this fact in mind we can employ a neat trick. Here it goes: The early-evening position of the Big Dipper tells you what season it is. This isn’t exactly a new insight, given that I’ve read reference to it in 2,500-year-old Chinese writings.

Keeping in mind that we’re talking about the early-evening position, if the Big Dipper is under Polaris, then it’s autumn. That’s the case right now. Given Saipan’s low latitude, the Big Dipper, when under Polaris, is also under the horizon. This time of year it’s about 2:30am before the Big Dipper finally hoists itself above the horizon. That’s why it’s a sight for night owls at present.

But it’s not usually just for night owls. By mid-wintertime, the Big Dipper will migrate to the right side of Polaris for its early-evening appearance; springtime will put the Big Dipper over Polaris; and summertime will put it left of Polaris. So it’s not usually stuck under the horizon in early evening.

I am, incidentally, talking about the viewer’s perspective here: Right, left, under, and over are used as they pertain to how you see them relative to Polaris.

Anyway, this Polaris and Big-Dipper merry-go-round is a yearly cycle. Now that you know the cycle you can read the seasons from the sky.

We can certainly enjoy looking at the Big Dipper without knowing the names of its stars. After all, our puny little Earthling names are merely arbitrary labels. But I’ll note the names anyway. Moving from the tip of the handle to the tip of the bowl: Alkaid, Mizar, and Alioth are the three stars of the handle, and then Megrez, Phad, Merak, and Dubhe are the four stars of the bowl.

If you take a look at Mizar, the second star of the handle, you may note a faint little companion star. This star is called Alcor. The pair, Mizar and Alcor, are called the “horse and rider.” Alcor is faint enough to be a good tester for sky clarity. In ancient times it was also an eyesight tester for military candidates, at least according to legend.

As cool as the horse and rider are, the most famous pairing in the Big Dipper comes from the two outer (away from the handle) bowl stars, Merak and Dubhe. If you connect Merak to Dubhe with an imaginary line, and then extend that line for five times the distance between those two stars, you’ll land close to Polaris. Merak and Dubhe are therefore called the “pointer stars.” This tidy arrangement is depicted, among other places, on the flag of Alaska.

The middle five stars of the Big Dipper (meaning all but Alkaid and Dubhe) are moving through space on a common trajectory, sort of a stellar version of fighter jets flying in formation. It’s thought that these stars were launched from the same cosmic cradle.

Have you ever looked at the Big Dipper and wondered how far away the stars are? Well, those five middle stars I just mentioned are within a tight band of distance. Estimates for distances vary, but my reference puts these five at about 81 light-years, give or take a few either way.

The two outliers that aren’t part of the middle five, Alkaid (tip of the handle) and Dubhe (tip of the bowl), are more distant, at 101 light-years and 124 light-years, respectively.

I’ll note that a light-year is about 6 trillion miles. So if you ever want to keep the kids busy on a long trip, you can have them calculate some star miles for you. That’ll shut ‘em up for awhile, or at least until they learn scientific notation.

If you’re working the graveyard shift, the next time you take a coffee break have a look toward the north. The Big Dipper has enchanted people for thousands of years, so you’re part of a long tradition.