Sirius is the brightest star in the night sky, perched on the nose of the constellation Canis Major, which is otherwise known as the Big Dog. Because of that, Sirius is called the "dog star," and it dominates the winter sky as part of what I call "Orion's Gang" of bright constellations. In Greek and Roman mythology Canis Major is Orion the Hunter's biggest and best hunting dog.

Sirius also is known as the star of winter, but now that we're more than halfway through spring, the Dog Star has left our evening skies, not to be seen again in the early evening until sometime next November.

The very bright star Arcturus, the second brightest star in the sky, rules late spring and summer skies and is doggone close to Sirius in brightness. I call it the star of summer, and it's so easy to see.

Just look for the brightest star you see in the high southern heavens. I don't think you'll need much help locating it in our Butler skies, but just to make sure you're indeed gazing at Arcturus, use the nearby Big Dipper, which is now hanging upside down in the high northern sky.

Just follow the curve or arc of the handle of the nearby Big Dipper beyond the end the dipper's handle and you'll run right into Arcturus. Just remember the old adage, "Arc to Arcturus."

Arcturus is a Greek name that translates to English as "guardian of the bear," That's a little contradictory, though, because Arcturus is the brightest star of the constellation Bootes the hunting farmer, which, according mythology, is hunting down the Big Bear constellation, otherwise known by its Latin moniker as Ursa Major.

As I told you a few weeks ago, the Big Dipper outlines the rear end and tail of the Big Bear and is the brightest part of Ursa Major. Honestly though, Bootes looks much like a giant kite with Arcturus at the tail of the kite.

You might think you're looking at Mars because of its bright orange hue you can easily see with the naked eye, even in heavy city lighting. Mars also is in our night sky right now, but much lower in the southwestern sky near the constellation Leo the Lion.

Just call up the complete May Star Map on www.lynchandthestars.com website to find Mars. Every two years, Mars rivals and can even overtake Arcturus in brightness as our Earth and the red planet swing close by each other as they orbit the sun.

Arcturus' reddish-orange hue is because it's what's known as a red giant star, a star that's temporally, at least in astronomical terms, bloated out as it's running out of hydrogen fuel in its nuclear fusion furnace core.

Its reddish color is because of the fact that it has cooled off as it has expanded. You still would get big time hot flashes as you approached Arcturus in a spaceship because it's still burning at 7,300 degrees at its outer layer. Our sun, by comparison, burns at just more than 10,000 degrees.

Arcturus, however, is more than 25 times the diameter of the sun with a girth of more than 22 million miles. Arcturus' brightness in our sky is mainly due to relatively close proximity to our sun and solar system. It's about 215 trillion miles away, and believe it or not, that's close for a star.

Its hasn't always been that close though. Arcturus is a very fast traveler in our Milky Way galaxy, definitely in the left lane on the interstellar speedway.

Actually, all the stars in our sky are moving along in all different directions and speeds as they orbit around the center of the galaxy. It certainly doesn't seem like that because we still see the same constellations in the sky people have witnessed for thousands of years.

That's because the stars are so far away, even at their breakneck speeds among each other, we can't detect any kind of movement. That's why up until about 300 years ago we thought stars were fixed in the great beyond of space as our Earth rotated beneath.

It was Sir Edmund Halley, the same guy for which the famous comet is named after, who detected changes in Arcturus' position among nearby stars in the sky by comparing ancient star charts with what he was observing in his time.

Since then, it's been determined Arcturus travels to the beat of a different celestial drummer, racing toward the direction of our solar system at more than 90 miles per second.

In the time you've taken to read this column it has traveled more than 500 miles closer to us. Arcturus is cruising along so fast it changes its position among the stars one full Moon width every 10 centuries.

That's very fast in comparison to other stars. It's thought by many astronomers that as little as 500,000 years ago, Arcturus wasn't even visible in the night sky.

At 37 light-years away, it's about as close as it's going get to us. As a matter of fact, in about 500 million years, it will fade into oblivion. We won't ever see Arcturus again because by the time it makes its own circuit around the galaxy, our Earth and sun won't be anywhere near it.

So don't take the big orange star for granted, it's just passing through!

Celestial travels

Speaking of moving along, the growing waxing moon in our evening sky will pass close by three planets this week in the evening sky as it migrates eastward at 13 degrees every 24 hours.

On Sunday, you'll see a thin crescent moon just to the upper left of the very bright planet Venus in the low western sky.

On Wednesday night, it'll pass just below Mars in the southwestern evening sky. And next Saturday evening, it slips just a little below Saturn, a little higher up in the southwest sky. Just check my website for more charts and details.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and author of the book "Pennsylvania Starwatch," available at bookstores and at his website www.lynchandthestars.com.