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ROBERT SIEGEL, HOST:

Time now for our resident astrophysicist Adam Frank. He's on a quest to help people find their inner scientist by exploring how ordinary everyday stuff can be turned extraordinary. Today, how looking up to the winter sky can offer a lesson worthy of Charles Dickens.

ADAM FRANK, BYLINE: Ebenezer Scrooge was famously visited by three ghosts in "A Christmas Carol." The past, present and future all converged on poor Scrooge in an effort to save him from his own narrow vision and wake him up to the wonders of the life that was right there before his eyes. As we navigate the frantic pace of this holiday season, we, like Scrooge, might stop to let the past and the present and the future converge on us for the same reason. All we have to do is step outside and let the winter night sky become a time machine.

OK. Once you get out there, your job is to find a star and focus on it for a second. So here's the question. Are you seeing that distant sun as it is now, right now? The answer, of course, is no. We never see the sky as it is, but only as it was. You see, the speed of light is not infinite. So that means it takes some time for light to travel across any distance in space. So when you stare into the depths of the night sky, like looking at a distant star, you're also looking back in time.

Catch a glimpse of a relatively nearby star and you're seeing it as it was when the light left its surface, perhaps when Lincoln was president, say, if the star is 150 light-years away. Stars near the edges of our own galaxy are seen as they appeared when the last Ice Age was in full bloom. The light from the star is a messenger from some other now that is long, long gone.

And here's another twist. All the other stars in the sky are at different distances, which means different depths in time. So that one now you're experiencing, seeing all those stars, is really made up of an infinite number of thens. This present moment, in other words, is made of many, many pasts.

And you can't dismiss this overlapping-pasts-making-up-the-present thing as some kind of astronomy weirdness. No. It's the fabric of everything you experience. When you look at a mountain peak 30 kilometers away, you see it not as it exists now but as it existed a 1/10,000 of a second ago. And even gazing into your child's eyes, you see her not for who she is right now but who she was, a mere 10-billionth of a second in the past.

The simple fact that nothing can travel faster than the speed of light means all of us - every man, woman and child - share the same predicament. We are all profoundly separated and yet deeply connected at the same time. And just as Scrooge's initially frightening ghosts turned out to be messengers of hope, the deepest truths of science and the infinite night are there for us as well. What else can we do but live with compassion and reverence and joy?

SIEGEL: Adam Frank teaches at the University of Rochester.

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