Diagram of Capella location in the early evening.

Four out of the five brightest stars we can see are now readily visible in the early evening Butler celestial dome.

Of course, the sun is our brightest and closest star. Once the sun has finally set this time of year, the brightest star is Arcturus, lighting up the southern sky, and next in line is Vega, showing off its brilliance in the high eastern sky.

Capella is the fifth brightest star we can see from our planet. Look for it as soon as you can in the low northwestern sky, poking out of the evening twilight. Don't wait too long to look for Capella though, because it slips below the horizon shortly after 11 p.m.

Even though it’s only fifth place in stellar brightness, Capella’s claim to fame is that it’s the brightest nighttime star that we see most often in our northern hemisphere.

Capella can make that claim because it’s the nearest, brightest star to Polaris, the North Star. Polaris marks the position of the north celestial pole. Every celestial object we see in the sky — day or night — whether it’s the sun, the moon, planets or stars, all appear to rotate around the North Star Polaris once every 24 hours. Polaris is the “linchpin” (sorry) of the sky because it shines directly above the Earth’s terrestrial North Pole.

If we lived at the North Pole, the North Star would be directly overhead, and everything in the celestial dome would pivot around it. Around here, we live about halfway between the North Pole and the Earth’s equator, so in our sky, Polaris is permanently fixed about halfway between the northern horizon and the overhead zenith.

Stars close to Polaris in the sky, like those that make up the Big Dipper and Little Dipper and the W-shaped constellation Cassiopeia, are so close to the north celestial pole that they’re always above the horizon, moving in a tight circle around the North Star. They are called circumpolar stars, and we see them night after night.

Capella is not quite close enough to Polaris to be considered a circumpolar star, but it’s close. Because of its northward position, Capella can be seen in our evening skies from late August to mid-June. Throughout the year it never goes an entire night without making at least a brief appearance.

Astronomically, Capella is around 42 light-years away, with just 1 light-year equaling nearly 6 trillion miles. While it looks like one giant star, it’s actually made up of four stars, two binary systems of stars, all revolving around each other. In each of the binary pairs, one of the stars is a huge giant, way larger and more massive than our sun, and the smaller star is considered a red dwarf, way smaller than our sun.

According to Greek mythology, Capella is known as the "goat star.” That’s because it’s the brightest star in the constellation Auriga the Charioteer. The constellation Auriga basically resembles a lopsided pentagon that’s supposed to be a retired chariot driver turned goat farmer, with a mama goat on his shoulder and baby goats in the crook of his elbow.

How you get all of that out of a lopsided pentagon is beyond me. There must have been quite a party when that constellation was conjured up! Capella is supposed to mark the position where the mama goat is sitting on the chariot driver’s shoulder, and that’s why it’s known as the goat star.

Unfortunately, all we can see right now of the constellation Auriga in the early evening is Capella. By early August, though, the lopsided pentagon will be available for very early morning viewing in the pre-twilight northeast sky.

Until then, all we have is Capella, or what I like to call the "Old Faithful” of nighttime stars!

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