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All posts for the month July, 2007

The Night Sky

In her column in Parade Magazine, a writer named Marilyn vos Savant made a list of “Questions too Funny to Answer.” Some of the questions were truly funny, belying people’s mis-understanding of science. Sad, in a way.

But, the saddest question, one that I didn’t find to be funny at all (and I’m surprised she listed it as “funny) was this: “Where did all the stars go? In the ’50s, the sky was loaded with them.”

It really isn’t even a dumb question. It’s a query that reflects a changed perception of the sky: we’re not seeing as many stars as we used to. Back in the ’50s we didn’t have much light pollution as we do now. Populations were somewhat smaller, and we were scattered more. Less light pollution per square meter, you might say.

Today, we light the night sky up with photonic pollution that tells the universe, “Look here! These people have money to burn!” Because, of course, when we light the night sky unnecessarily, we’re wasting money. And harming the environment in more ways than one.

If you ever have a chance to be in a truly dark-sky site, you’d see why I label the night sky as one of the seven wonders of the universe. To quote David Bowman in 2001: A Space Odyssey,, “My god, it’s full of stars!”

And that gorgeous scattering of distant starlight is what set our minds wondering throughout the centuries. They caused us to wonder about what they were, how they got there, what makes them shine, and what will happen to them in the future. The science of astronomy, followed by astrophysics, augmented by physics, planetary science, atmospheric physics, and so many others, flowed from our wonder about the night sky.

Star Death

The Kepler supernova remnant (courtesy Chandra X-Ray Satellite Center).

The Kepler supernova remnant (courtesy Chandra X-Ray Satellite Center).

So, from star birth we get star death. That follows, sure as…um… death and taxes. These things move in cycles. Starbirth regions almost always have some elements created by the deaths of the stars that went before them. Much as dying vegetable matter seeds a field here on Earth with the essential nutrients for the next generation of plants and animals, old stars recycle themselves into interstellar space. The elements they leave behind—carbon, nitrogen, oxygen, on up to silver, gold, and iron, and even the radioactive elements like thorium and uranium—get re-used in newborn stars and planets. It’s a pretty efficient mechanism for the universe to re-create itself through the billions of years it has existed, and it will continue for as long as there are stars to give off material.

Of course, the most famous stardeath sites are supernovae, particularly the kind known as Type 1a, which occur when massive stars explode and hurl their outer layers to interstellar space.

Planetary nebula M2-9, from Hubble Space Telescope. Could our own Sun look like this, four or five billion years from now? Its destined to become a planetary nebula, pushing its atmosphere out to space as it dies.

Planetary nebula M2-9, from Hubble Space Telescope. Could our own Sun look like this, four or five billion years from now? It's destined to become a planetary nebula, pushing its atmosphere out to space as it dies.

There are other ways for stars to die and pass on their “legacy” of elements to the cosmos. The Sun won’t die as a supernova, but it will swell up to become a red giant. Much of its mass will get blown off to space, and THAT mass will also be recycled into new stars a few billions of years from now. There’s evidence that material from several dying stars provided the seed material for the Sun and planets, which puts us and our home world smack in the middle of the cosmic cycle of life and death.

Regions of stardeath are nearly everywhere we look in our own galaxy and in countless other galaxies, too. They look remarkably similar, a testament to how the laws of physics and astrophysics work across time and space.