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18 September 2007

trails of stars that never set as they circle the South Pole

Click once or twice. In some magnifications, the concentric circles will generate shimmering Moire interference patterns -- not an inherent phenomenon of the stars and star tracks themselves, but a common optical illusion of dense sets of curves.

Image and text © 1979 Anglo-Australian Observatory, photograph by David Malin.

By pointing a camera towards the south (or to the north in the northern hemisphere) at night, we can record the paths of stars which never set. They appear to circle the apparent position of the Earth's axis of rotation projected on the sky. The elevation of this position above the local horizon indicates our local geographical latitude, about 30 degrees south at Siding Spring. The angle swept out by the arcs is an indication of the exposure time, which was about 10.5 hours on 400 ISO colour film. This kind of exposure is only possible from an extremely dark site. More information on relationship between the measurement of time and star trails is in the caption to a similar picture here.

During the long winter nights observers using AAT occasionally peer outside to inspect the weather and as they walk around the dome their lights produce the irregular lines at the catwalk level. The upper part of the dome is however illuminated by the light of the natural night sky and stars alone.

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The Anglo-Australian Observatory is in Siding Springs, New South Wales, Australia. Hire a car in Sydney and drive northwest. Keep driving. Drive some more. Stop when you get to a town called Coonabarabran, then ask for directions to the observatory.

This world-class telescope for the Southern Skies is there because they need dark skies, and dark skies are now only to be found far from cities.

In school when you learn about the goddesses and gods and heroes and heroines and animals and monsters who live in the night sky, you usually don't understand what they're talking about. The stories are from an age long past when the skies were so clear that the connect-the-stars pictures screamed bears and serpents and scorpions, archers, huntresses, chariots, queens. Everyone could see them all on two hundred nights of the year, and it only took a little storytelling coaxing to make them all come alive.

Now a night sky like that is an extremely rare event for most people, and it's startling. I've seen such skies in the Australian desert in Alice Springs, and on ships in the Atlantic, the North Sea and the Baltic.

This is the slow and silent theft, a robbery so slow that we didn't even notice something of spectacular value was being taken from all of us, so no one ever called the police or complained to the government. Most of us live in and around cities, and most of the damage is caused by a century of the artificial light from cities and suburbs and industrial zones.

The International Dark Sky Association works to return this heritage to us, not by plunging us into darkness, but by shifting our artificial lights to kinds of lights that produce wavelengths that don't corrupt our view of the night skies, and aiming our lights carefully, to illuminate just those near-ground things for our safety. We don't need to illuminate the skies above us to be safe at night.

In a few weeks the polar bears will migrate through and around the town of Churchill, Manitoba on Hudson Bay in Canada. You can take a spectacular old train from Winnipeg through the wilderness, two and a half days in each direction, to get there. Churchill is also said to be the best spot on Earth to see the Northern Lights, the Aurora Borealis, most active and intense during the winter.

One night in the woods outside Miletus (in modern Turkey), the world's first full-time philosopher, Thales, fell down a well. He yelled for help until a slave girl heard his cries and helped haul him out. She asked him what had happened, and he said he'd been walking around looking up at the sky. "You old fool," she yelled at him. "You were paying so much attention to the stars you didn't see where your feet were going!"

But in those days, there was so much to see by looking up at night. Millions of fixed stars. Five wandering planets you could see with the naked eye. Some of them would go in one direction for months, and then stop, and then go in the opposite direction for a while. The Moon, of course, in all its waxing and waning phases. And oddball transient things that came and went, appeared and disappeared without warning -- comets, meteors, amd flocks of shooting stars a few predictable nights of the year. Sometimes the full Moon would turn blood red and disappear without warning, and then come back. During the day, now and then the Sun would vanish and return, too.

And you were there to see it all and wonder what it all was and what it all meant and why it behaved like that. Sometimes things so strange and beautiful that parents would wake their little children and take them outside to see them in the middle of the night.

Now we know what most of it is and what most of it means and why most of it behaves like that. We just can't see very much of it anymore.


StereoBalls said...

I finally got back to my blog, so if you're still interested in news from Russia I'd be glad to help :)

Vleeptron Dude said...

Hey hey hey hey stereoballs! Приветствовать!!

How's the mp3 business? How are you doing?

Yeah, uh ... what up with Viktor Zubkov? Had you ever heard of him? What's your take on him? Just tell us *anything* that you think is interesting in Russia now!