The Super Bright Star Which Shines Overhead
Every Year On The Autumnal Equinox
Horkheimer: Greetings, greetings fellow star gazers. Next Monday September 22nd is the first day of autumn, the autumnal equinox. But did you know that if you go outside any night during the first week of autumn of any year and look straight up you will see one of the brightest stars in the heavens almost overhead? And that our Sun and Earth are actually flying toward it and getting closer every day? Let me show you.
O.K. we've got our skies set up for any clear night the first week of autumn between the hours of 8 and 9 p.m. your local time. And if you look straight up almost overhead you will see an extremely bright star right next to four dimmer stars which if connected by lines would make a lopsided rectangle which is more properly called a parallelogram. These stars plus a handful of others make up the ancient constellation Lyra the harp.
But Lyra's brightest star Vega is the real attention grabber. It is the fifth brightest star and compared to our Sun is a doozy. For starters while our Sun is 865 thousand miles wide, Vega is over twice as wide, two million miles. And Vega's bluewhite color tells us that it is a super hot star, much hotter than our own yellow-orange Sun. In fact our Sun's surface temperature is a mere ten thousand degrees Fahrenheit whereas Vega's is a blistering 17,000 degrees. So because Vega is much bigger and hotter it is 60 times brighter! Talk about getting a suntan in a hurry!
But one of the really nifty things about Vega is that it once was and will again be our North Star, a much brighter one than our current North Star, which is the end star of the handle of the Little Dipper. You see the North Star is simply the star directly above our Earth's north pole, the one towards which our Earth's axis points. But because of a regular, very slow wobbling motion of our Earth, like a top slowing down, our Earth's axis doesn't always point to the same spot in the heavens. In fact our Earth's axis traces out a great circle in the sky. Right now our Earth's axis is pointed to a spot on that circle very close to our current North Star.
But the Earth's axis slowly drifts, constantly changing where it points in that circle. A hundred years from now it will point even closer to our current North Star but a thousand years from now it will be well past it. And once every 26,000 years it points to Vega. So 14 1/2 thousand years ago Vega was the North Star of our cave man ancestors and Vega will be our North Star once again eleven and a half thousand years from now. Wow!
But what I really love about Vega is that it marks the direction our Sun and Earth are headed. In fact our Sun and Earth are racing towards Vega at the incredible speed of 12 miles per second. But Vega is so far away it would take our Sun almost 500 million years to reach it. And unfortunately by the time we get there Vega will have already moved. So don't pack your bags for Vega yet.
Just go out any night next week the first week of autumn between 8 and 9 p.m., look overhead and contemplate the incredible beauty of this brilliant blue white star. And in your mind's eye see if you can almost feel our Earth and all of us on it zooming through space at 12 miles per second toward it. You know sometimes I feel as if I almost need a seat belt. Keep looking up!
Jack Horkheimer : Star Gazer....
