North Star is central to all

I know this may be old hat to a lot of regular readers of my column and veteran stargazers, but for the sake of new fans of the night skies I want to go back to the basics — the Big Dipper and the Little Dipper.

If you’re just getting started with stargazing, the Dippers are a natural launching pad to get your love affair going with the celestial theater and understanding basic celestial mechanics.

This is a great time of year to get started as the Big Dipper is riding high in the higher northern skies these early spring evenings. While much of the cold of the winter is in the past you have to stay up much later for stargazing.

Get an afternoon snooze in because you’ll have to wait until around 9:30 p.m. to see the Big Dipper perched upside down just below the overhead zenith. These seven stars are some of the brightest in the sky.

Two stars in the Big Dipper’s pot section opposite the handle, Dubhe and Merak, can point you to Polaris, otherwise known as the North Star.

Draw a line between Merak and Dubhe and that’ll act as a pointer to the North Star. Continue that line down from Dubhe about three of your fist widths held at arm’s length and you’ll be right at Polaris, or darn close. There should be no doubt in your mind because the North Star is the only bright star in that immediate area.

Polaris is certainly not the brightest star in the sky, but it sure is an important one. I call it the “Lynch pin” of the night sky because everything in the heavens, even the sun and the moon, complete one circle every 24 hours around the North Star.

That’s because the North Star is shining pretty much exactly above the Earth’s North Pole. If you’re standing at the North Pole, Polaris would be more of less directly overhead at the zenith and everything in the celestial sphere would circle it every night and day.

Stars close to Polaris would make tight little circles around it. The farther stars are away from Polaris in the sky the larger and larger their circles will be around the North Star. But no matter how far or near to Polaris, all stars would make one complete circle in 24 hours.

Since we don’t live at the North Pole but just over halfway between Earth’s North Pole and equator, Polaris around here is not overhead but almost halfway between the northern Butler horizon and overhead.

The general rule of the thumb here is that the altitude of Polaris above your northern horizon equals your degrees in latitude.

Stars and constellations in the northern part of the sky make such small circles around Polaris that they never get below our horizon. They’re called circumpolar stars, such as the stars of the Big and Little Dippers.

Stars farther south from Polaris have such large circles that part of the circuit lies below our horizon. That makes most of the stars in our sky rise in the east and set in the west.

The further south a star is from Polaris the more time it’ll spend below the horizon. In fact stars in the low southern sky spend much more time below the horizon than above it.

The North Star is also the brightest star of the Little Dipper, shining at the end of its handle. The Little Dipper is nearly upright below the Big Dipper and is a lot tougher to see, especially in city lights.

Look for two moderately bright stars to right of Polaris. They’re Kochab and Pherkad, on the opposite side of the Little Dipper’s pot section. The other two stars in the pot and the other two handle stars can be really tricky to see if there’s any light pollution where you’re viewing.

The Little Dipper is also known as Ursa Minor, the Little Bear. The Big Dipper is actually just the rear end and tail of the much bigger constellation, Ursa Major, the Big Bear.

As you can see in the diagram the stars that outline the derrière and tail of Ursa Major are by far the brightest members of the great celestial beast.

Celestial hugging this week

The planet Jupiter is now at its closest point to the Earth in more than three years this week at just under 410 million miles away.

Without a doubt it’s the brightest starlike object through the night. Over the next several nights the virtually full moon will be passing it by from night to night.

On Sunday night the moon will be above and just to the right of Jupiter in the low eastern sky. On Monday night it’ll be kissing Jupiter just to the lower left of the big boy of our solar system. On Tuesday evening the moon will be farther away down and to the left of Jupiter. Don’t miss this show.

Make the stars your old friends

If you have any astronomical questions or want me to write about something you’re seeing in the night sky, drop me a line at mikewlynch@comcast.net.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul and is author of the book, “Stars, a Month by Month Tour of the Constellations” published by Adventure Publications and available at bookstores and at http://www.adventurepublications.net.