What you see in the sky is not always reality. There are many illusions up there. Whenever you look at the starry sky, you are not seeing the stars in real time. In fact, you look into the past to varying degrees. Everyone knows that the stars we see at night are far away. Trying to express those distances in miles involves using trillions, and with the exception of the national debt, most of us don’t use trillions that much. It’s hard to wrap your mind around the concept of a trillion anything. Here we are talking about a thousand billion!
It is easier to express the stellar distance in light years. A light-year is the distance a beam of light travels in one year, moving at the speed of light at just over 186,000 miles per second. If you do the math, that comes out to about 6 trillion miles for just one light year. On average, most of the stars you can see in the heavens with just the naked eye are about 10 light-years away to about 3,000 light-years away.
Alkaid, the star at the end of the handle of the Big Dipper, is 101 light-years away, or about 606 trillion miles. Because it is 101 light years away, it took the light from Alkaid 101 years just to reach the eye. When you look at Alkaid, you don’t see it as it is now, but as it was in 1921, when about 20 percent of American homes had bathtubs. We can easily spot a much more distant star in the night sky right now. It is Deneb, the bright star that marks the tail of the constellation Cygnus the Swan, flying high in the southwestern evening sky. Deneb is about 1,500 light years away, so we’re seeing Deneb as it was around 500 AD, long before the United States existed.
As far away as Deneb is, there are many other even more distant stars, many of which we can see with the naked eye. The question I get asked a lot is if some of the stars you see in the night sky might not be around anymore. Are we only seeing the light from a star that has met its maker? Have they already exploded in a colossal supernova explosion, as with supermassive stars, or have they shrunk into white dwarfs like our sun? Rest assured that 99.9999 percent of the stars you can see with your eyes or a small telescope are still alive and passing. The lifetime of a fully functioning star is at least 2 billion years, and there is no way, no matter how many carrots you eat, that you can see with the naked eye a star that is 2 billion light years away. All those shining ones in the heavenly dome are still there.
Another major illusion in the sky is that the stars you see are single stars standing alone in space. Most of them are actually star systems. Some are binary stars, where two stars orbit each other. Some may be triple, quadruple, quintuplet or even more star systems, all member stars orbiting each other in sometimes very complicated cosmic dances. Our sun is itself the exception rather than the rule.
There are also double stars in the sky that are not members of the same star family, but are stars that happen to be in the same line of sight from Earth. They’re called double optics, and a great example is in the handle of the Big Dipper. The star in the middle of the handle that you immediately see is Mizar, but if you look just above and slightly to the left of Mizar, you’ll see a fainter star called Alcor. Mizar is about 78 light-years away, and Alcor is just over 81 light-years away. Physically, they have nothing to do with each other.
Another great double star, probably the most beautiful in the sky, is Albireo. This marks the head of Cygnus the Swan, also known as the foot of the famous “Northern Cross” of Cygnus. To the naked eye, Albireo looks like a single unassuming star, but even with a small telescope you can see two stars, one with a distinct bluish hue and the other with an orange glow. They are a gorgeous duo of stars, about 400 light years from our backyards. It is not known if they orbit each other in a binary system, but if they did their orbit around each other would take about 100,000 years.
Celestial is happening this week
On Monday night, November 28, the new crescent moon passes just below the moderately bright planet Saturn in the south-southwest sky. On Thursday evening, look for the first quarter moon just below the much brighter planet Jupiter in the southeastern sky
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Mike is available for private celebrity parties. You can contact him at mikewlynch@comcast.net.
