Colorful stars reveal their life stories and future deaths

With spring rapidly heading in the direction of summer, our world has become a burst of colors. There’s even color to be found in the late-spring Western Washington night sky, but you have to dig for it a little.

Although they may look like it, most stars are not just little white lights. Even with the naked eye, you might be surprised to see that there are tinges of color in many stars, mainly red or blue. The color of the star can actually tell you a lot about it, especially its temperature.

It’s really very simple. The bluer the star, the hotter it is, and the more red that distant giant ball of glowing gas is, the cooler it is. It’s like staring into a campfire. The coolest flames are the reddish ones and the hottest are the bluish ones in the middle.

A good example of a blue-tinged star is Vega, a really bright summer star on the rise in the eastern sky. Around 9:30 to 10 p.m. look for it in the east-northeast. By 10 p.m. it will be about 30 degrees above the horizon, which is about three fist-widths at arm’s length. If you can’t see it with your naked eye, you’ll certainly see that it has a bluish tinge when using a pair of binoculars. You’re definitely looking at a hotter star, over 15,000 degrees at its outer edge and a lot hotter inside.

The color of a star can also help you deduce something about its fate. Hotter stars have shorter life times. Deep in the cores of all stars are giant nuclear fusion furnaces that convert hydrogen fuel into helium and tremendous amounts of energy. Hydrogen is the fuel of all stars, and the hotter stars such as Vega go through their hydrogen much faster than cooler stars.

Because of that, hot stars like Vega have life spans of only a few billion years. Stars like our sun are cooler, about 10,000 degrees at the surface, and have a longer life span of 8 to 12 billion years. If you’re a star and you want to live a long time, be a slower burner like our sun. Astronomers also know that Vega is more than three million miles in diameter, almost four times larger than our sun, and more than 26 light-years (about 150 trillion miles) away.

A great example of a reddish cooler star is also in the eastern half of the sky, and a lot higher up than Vega. Arcturus is actually a very bright orange-red star in the high southeastern sky. It’s the brightest star in the constellation Bootes, which looks like a giant sideways kite with Arcturus at the tail of the kite. A really good way to find Arcturus is to use the nearby Big Dipper. Follow the curve or arc of the handle beyond the end of the handle and you’ll run right into Arcturus. Just remember the saying “Arc to Arcturus.”

Arcturus is definitely cooler than both Vega and our sun, less than 7,000 degrees, but its reddish hue is a sign that Arcturus is in the stages of the end of its life. Like many other bright reddish stars it has nearly depleted what’s left of its hydrogen fuel and has bloated out into a red giant star. The details get a little hairy, but as a star begins to run out of hydrogen at its core, nuclear fusion starts taking place at the more outer layers of the star, causing it to bloat out into a red giant.

Eventually, in about 1 to 2 billion years, Arcturus will blow off what’s left of its gaseous shell and will shrink into a very small white dwarf star. Our own sun will bloat out to become a red giant in about 5 billion more years, and when it does, it will swallow up the planets Mercury and Venus and will fry and boil everything and everybody on Earth. Now there’s a day brightener. The final fate of our sun will also be one of a fading white dwarf, not much bigger than Earth.

So now you know that just by scanning the starry skies, with or without binoculars, you can tell a lot about stars just by looking for a little bit of color.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and author of the new book “Washington Starwatch,” available at bookstores and on his Web site, www.lynchandthestars.com.