Wednesday, February 10, 2010

Starlight musings

It takes about five hours flying time to get from my home in New England to this island in the Bahamas. Light can travel the same distance quicker than a snap of my fingers. In fact, light could make the round trip 100 times in a snap of the fingers. Light travels fast.

Bonfire on the beach last evening under a moonless starry sky, the Milky Way arching overhead, red Mars blazing away in Cancer. Actually, of all the objects in the sky, Mars is the only one that's not blazing. As everyone knows, the light we see from Mars is sunlight. Twelve minutes for light to leap from the Sun to Mars -- a thousand snaps of the fingers, more or less. Then four minutes for reflected light to bounce back to Earth. The sunlight I see from Mars is 16 minutes old.

The closest star in the sky is Sirius -- or at least the closest we saw as we sat on the beach. The light from Sirius is nearly nine years old. So there.

It takes eight minutes for light to get from the Sun to Earth. Five hours to get to Pluto. Think of our solar system as ten light-hours wide, one-half (more or less) of the first day of the year of that calendar hanging on your wall. Go on, get down the calendar and in the box for January 1 draw a circle half as wide as the box. That's the Sun and all of the planets. The next closest star -- Alpha centauri -- is 4.6 light-years away. Four-and-a-half annual calendars cut out in weekly strips and all those strips pasted end to end. Got that? I wonder why I never thought of doing it when I was teaching astronomy. Cutting up and pasting calendars to represent light-time. Rolling it out across the college quadrangle. To really get a sense of how far apart are the stars.

And all those Milky Way stars spilling across the sky! Some of them are a thousand light-years away. A thousand years for light to get from there to here, traveling so fast that it can make 100 round trips between New England and here in the snap of the fingers.

But I'm babbling. And in the time I say "babble," light can travel from here to the Moon.