In the Twinkle of a Star

11/19/06 – 11/26/06
by C. Zaitz

Have you ever wondered why the stars twinkle? We all know the song by heart, but it never really tells us why they twinkle, twinkle. The song wonders what they are, the little twinkling stars. I don’t want to ruin the song for anyone, but there are answers to both questions.

We don’t have to go very far to study a star. There’s one about 8 minutes away (going at the speed of light, of course). Traveling 70 mph, it would take us 1,328,571 hours, or 55,357 days, or 152 years!

Luckily we don’t have to go there. We can collect information from the sun just by standing outside with a telescope or other device to collect its light. The information we gather tells us the story of the Sun. It’s a middle-aged star, fusing hydrogen atoms in its core to produce enough energy and light to keep its planets warm and cozy. Well, not all its planets, just the lucky closer ones.

All stars are giant collections of atoms, mostly hydrogen. Stars are so mammoth that the great pressures near their centers allow for normally repulsive forces to be overcome and for atoms to fuse into new elements like oxygen and carbon. In fact, without the stars’ atom-fusing abilities, we’d have been a pretty boring universe of hydrogen and helium with a sprinkling of lithium for spice. No mercury, gold or silver. They came later, from stars.

So when you look up at the stars, you can think of them as giant element-producing ovens, getting very hot from churning out planet-making elements like silicon and nitrogen, stuff that ends up as sand and air. Think of that next time you’re on the beach, looking at the pretty sunset. It all came from some star, ancestor to our own sun.

While we’re at the beach, we can also figure out why stars twinkle. Just look into the water. See how the pebbles on the bottom seem to jump and hop around as the waves wash over them? The water is the medium that the light must travel through to get to our eyes. Light likes to go straight in a vacuum, but will change speed or direction in thicker stuff, like air or water, especially if they are moving. The water at the beach is moving a lot, so the pebbles seem to jump around madly. The air is also moving and therefore “bending” light, but not as much, since it is much less dense than water.

However, there is much more air above us than below us. There is a veritable ocean of air above us, and we must look through this “ocean” to see the stars. The starlight may have been traveling in the vacuum of space for millions of years, steady and true, all the way to earth. But when it gets to our atmosphere, it gets jostled, nudged and pushed around by moving air currents. By the time we get to see it, starlight can be jumping around like a drop of water on a hot frying pan. In winter, the atmosphere is often more turbulent, so you will see lots of twinkling and winking of starlight. It’s annoying in a telescope, but can be very pretty to the naked eye. So while you’re humming the song, you can enjoy the very distant stars twinkling and making someone a new beach!

Until next week, my friends, enjoy the view.