Sunday, November 18, 2007

Why was the sky bright at the time of Christ's birth?

When I was a child, I wanted to be an astronomer.

I was the nerd out there with the telescope. I sat out in the winter cold looking for comets. And I read about, dreamed about, and thought about the heavens much of the time.

But that career was not to be. Because I realized early on that my math skills were not sufficient for astronomy. (Most people who check "astronomer" as their job title finish an undergrad degree in physics, followed by graduate degrees specializing in astronomy. Physics requires math. Lots of math).

But every year around Christmas, I'm reminded of my interest in the heavens. I'll talk later about the star of Bethlehem. But today, I'd like us to ponder a line from Away in a Manger, in which we're told that "the stars in the bright sky/look down where He lay."

Some versions omit "bright," but it's in the original. And what "bright" brings to mind is an astronomy term called "Olber's paradox," which asks the question, "Why is the night sky dark?" Very briefly summarized, the paradox says if the universe is infinite, there should be stars at every point in the sky, and the night sky should be at least as bright -- probably brighter -- than the daylight sky. But it's not bright.

We do not know who wrote the first 2 stanzas of this hymn. I suspect that whoever the author was meant to say by the words that the sky around the birth of Christ were bright with stars -- a "brightness" that most of us seldom see, much less appreciate, given that most of us live in light-polluted areas.

Here's a summary of Olber's paradox. I got a book in the mail yesterday which deals with the question as well. It's Edward Harrison's Darkness at Night: A Riddle of the Universe. I'll review it here when I'm done with it.

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