Monday, December 23, 2013

"In a dark time, the eye begins to see"


Back to clear dark skies. Not as clear or as dark as when we came here 19 years ago, built Starlight House, and settled in for golden years of sky-watching. The airport got lights for nighttime operation. The Queen's Highway got street lights (of the worst kind for light pollution). And the new Four Seasons/Sandals resort, five miles north of our house, is all lit up so their customers couldn't see a star if they wanted to. But by comparison to our home near Boston, our little island is still an oasis of darkness.

Here's a recent APOD (Astronomy Picture of the Day) showing one of the most familiar star configurations in the sky -- Orion's Belt. Three hot blue stars, each vastly more massive than the Sun. That's them running diagonally across the photograph from upper left to lower right (click to enlarge). Nothing else in the photo is visible to the unaided eye.

What a mess of stars! And nebulae where even now stars are being born. There's the famous Horsehead Nebula standing out against the pink glow of hydrogen at lower right. How many stars? Go ahead. Count.

No, just kidding. If you started counting with a magnifying glass you'd be at it all day. And this is just a wee corner of our galaxy.

I'm sure I've mentioned here before that when I used to teach a course called The Universe to general studies students one of my set pieces was to push back the desks and use a one-pound box of salt to make a model of our spiral galaxy on the floor. The students were always dazzled at the number of stars. Then came the kicker. Let's figure out how many boxes of salt we'd need to have the hundreds of billions of stars in the Milky Way. I'd guide the students to a few judicious estimates, averaged for the class. Ten thousand boxes of salt! Sprinkled in a vast spiral as big as the orbit of the Moon. (If a salt grain were proportional to the actual size of a typical star, the grains should be thousands of feet apart.)

As often as I did that demonstration, I was as awe-struck as the students. And now, I lie on the terrace and gaze up into a warm, clear, dark sky, Orion climbing the inky dark in the East, and with a lifetime of practice I fill in the blank spaces with those myriads of stars we see in the APOD photo.