By Mike Lynch
At first glance when you gaze upon the stars, even in the dark countyside, they just look like little white lights of varying brightness.
However, with even a small telescope or a pair of binoculars you’ll see that many stars actually sport subtle colors to them. Sometimes you even see color in brighter stars with just your eyes.
Some pastels are easy to see like the red on Mars because of all the rust on its surface, but in most cases you just have to dig a little but you can make some really nice discoveries. Let me give you some example across the early evening April sky.
The easiest star color to see in Orion the Hunter is on Betelgeuse, an Arabic name that translates to “armpit of the great one.” Betelgeuse has a very distinctive orange-red glow to it. It’s also one of the biggest single things you’ve ever seen, with a diameter more than 500 million miles. Our sun isn’t even a million miles across.
Now by color contrast take a look at Bellatrix, the bright star across from Betelgeuse that marks the left shoulder of Orion. With a telescope or binoculars you should see that it has a very deep shade of almost purple.
The color of a star no matter how subtle it is can tell us quite a bit about its nature, especially its temperature: The bluer the star the hotter it is, and the redder it is the cooler it is. Yellow colors are in the medium range.
Astronomers have estimated by multiple methods that surface temperature of Orion’s armpit is just under 6,000 degrees, but the surface temperature on Bellatrix is 39,000 degrees.
Most of the other bright stars of Orion, such as the three stars in a row that make up his belt and Rigel at the knee cap, all have a slight blue tinge to them, but not nearly as blue as Bellatrix and are therefore not as hot.
Most reddish stars like Betelgeuse are classified as red giants, which are bloated stars reaching the end of their lives as they’re running out of hydrogen fuel. Depending on how massive they are they will either eventually shed much of their material away and what’s left shrinks down to what’s called a white dwarf star not much bigger than Earth.
This is the eventual fate of our sun in roughly another 6 billion years. Stars much more massive than our sun will go out with a tremendous bang. They become very unstable and burst out in supernova explosions. What’s left of those exploded stars shrink down to very dense neutron stars or possibly to the infamous black holes.
Most bluish stars are massive ones to begin with and are not long for this universe as they gobble up their hydrogen fuel at incredible rates. Compared to low mass stars like our sun, they’re short lived, lasting in some extreme cases less than a billion years. Our sun has an expected lifetime of 11 to 12 billion years.
The sun has a surface temperature of about 10,000 degrees and is considered by astronomers to be yellow-white. To the left of Orion in the western sky is the bright star Capella, the brightest star in the constellation Auriga. It’s also a yellow-white star, but Capella is actually a pair of stars revolving around each other about 42 light-years from Earth.
Both stars are way larger than our sun but similar to our sun in temperature at about 10,000 degrees, but it takes a big visual effort to see yellow pigment in Capella.
Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores. Check his website, www.lynchandthestars.com.
The Everett Astronomical Society: www.everettastro.org/.