Stars in the east

Weather permitting, Christmas weekend bodes well for shining celestial visitors

by Bob Berman
December 23, 2010 12:18 PM | 0 0 comments | 7 7 recommendations | email to a friend | print
Dots. Pinpoints. White specks on a dark background. Those are the starry heavens to the naked eye. It’s not Paris. Why does it thrill us?

No one can explain how this simple motif touches us so deeply. Perhaps it’s because our ancestors stared at the same sky. Being imprinted into our collective memories, it evokes feelings rather than opinions.

Before widespread rural electrification less than a century ago, most folks lived on farms, and moonless nights were absolutely crammed with stars. Maybe that’s why today’s city skies seem so Blade Runner-alien. In the Big Apple, no more than 30 anemic stars appear at a time. Our sense of wonder isn’t stirred by seeing a star, but rather lots of them together. It’s all or nothing. My experience is that people start to find the heavens beautiful when they show at least 500 stars at once.

We’ll get that here this Christmas weekend. Cold air is super-dry, and the winter stars – peppering the east – are the year’s brightest. A single brilliant yellow-white “star” dominates the west the first few hours after nightfall; that’s Jupiter. After 9 p.m., the blue Dog Star Sirius, to the lower left of Orion, becomes the dominant light. Then, a couple of hours before dawn, Venus rules. Always one dominant entity.

Want to see if your own skies are in the “excellent” class? Okay: Away from any town, can you see Orion’s belt, in the east, being surrounded by innumerable faint stars, like a swarm of fireflies? Then you’re in the sixth-magnitude realm and possess the full guaranteed 2,600-star inventory. Try this on Christmas Eve before 7:30 p.m. or Christmas night before 9 p.m. to avoid the Moon.

But it’s not just sheer numbers alone. To look great, stars need contrast. In bright ‘burbs, stars float against a milky background that’s inspirational for nobody. So the other vital factor is the degree of darkness between the stars.

The sky’s background can be unpleasantly bright from man-made lighting or simply high humidity and a fat Moon. When all these are thankfully absent, the biggest natural contributor to celestial milkiness is airglow. Caused by our atmosphere’s atoms fluorescing from solar ultraviolet (UV) energy, its intensity varies enormously. From 2006 to 2009, the sun’s UV emissions were at their lowest of the past century, which gave us the darkest night skies that we have ever seen. The new sunspot cycle #24 is starting to crank up the solar UV, so let’s enjoy these final months of intense sky-blackness.

Alternatively, you can go to places like Crestone, Colorado at 8,000 feet, where the air is not only bone-dry, but you’re also above a quarter of the atmosphere. Result: sharply reduced airglow and an inky darkness between the stars, paid for by your increased radiation exposure. (No, nothing is free.) Such a wondrous vista, resembling sugar sprinkled on black velvet, has been forever cherished by such disparate skywatchers as the desert-dwelling Arabs who named the stars and the magically mad Van Gogh who painted their portraits.

Finally, let binoculars take you from 2,600 stars to 35,000. Look at Orion’s belt or the Pleiades: beyond-words-spectacular. Moreover, the optics’ three-magnitude brightness boost changes your eyes’ color cutoff. Humans cannot perceive colors in stars fainter than third magnitude, which means that the “Seven Sisters” look white. But binoculars make them seem first-magnitude, and now their pastel blue is obvious.

Imagine loaning Hipparchus or Kepler a modern $30 binocular! They would have been your best friend forever.

So, yes, on so many levels: Who lives better than us?

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