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Palomar Shows Off New Laser
Observing >
Our favorite local --- and world famous --- observatory has just showed off a new toy, one that will allow it to continue to do premiere astronomy for a while to come.
Palomar Observatory, on Palomar Mountain in north San Diego County, for decades was The Place to go to do cutting-edge astronomy. The 200-inch mirror on the Hale Telescope (pictured at right) was the biggest in the world.
Then came bigger, more sophisticated telescopes, like the twin Keck Telescopes atop Mauna Kea in Hawaii, and Palomar's bright star began to fade.
One of Palomar's biggest problems, one in fact that assails every earthbound telescope, is that darned atmosphere of ours. For everything else our envelope of air is a pure godsend.
We need the atmosphere to provide us with oxygen, and pressure, and protection from deadly photons from space. It transports life-giving water, allows flight, warms us like a blanket, and so on.
But it makes an absolute mess of observing things in space. Why?
Have you ever looked at some distant object down a long street in the heat of the day? What you may remember seeing is what appeared as waves rippling above the asphalt making the distant object tough to see well. Look down that street with binoculars and the problem is just magnified. It's plain difficult to resolve much detail with all that distortion.
The same goes for anything above us. Trying to see through our atmosphere at night with the naked eye seems like no problem. We see the Moon and the planets and twinkling stars. But looking at them with a scope reveals that the same problem we have looking down the street at a distant tree rears its ugly head when we look up at distant stars.
Above us are tiny areas of warmer air next to cooler air moving invisibly through the skies. Such is the nature of our airy covering. The problem is that air pockets of even slightly different temperatures bend light differently, making the celestial object we are looking at appear to move about slightly.
So one may be looking at a star in the eyepiece of a telescope and the tiny point of light will literally jump around. (By the way, this atmospheric inference is why stars appear to twinkle.)
Planets are big enough in the eyepiece that they don't jerk about, but the details on their surfaces sure do, making them appear fuzzy or out of focus. Unfortunately, the way we learn in astronomy is to see more, not less, of the detail in objects, detail which reveals more and more of the way things are working up there.
What to do?! One possibility is to send a telescope above the atmosphere altogether, as was done with the famous Hubble Space Telescope, the satellite that has provided us with some of the most stunning images ever seen.
Obviously the Hale telescope at Palomar can't be sent into space. But maybe we can find a way to work with the atmosphere! How?
The latest, greatest thing in observational astronomy is called adaptive optics (AO). This method actually reads light coming in from a star and, via computer, "adapts" or reshapes a special mirror to compensate for the shaky atmosphere.
At the moment, Palomar and many other observatories use stars very near the object they are observing as corrective stars. As the image of the nearby moves about, the computer makes over 2000 corrections a second to try and steady it. The problem, though, is that you need a helper star really close to what you are observing. What if there is no star there?
You make your own star! And that's what's new at Palomar, where astronomers just recently, and successfully, tested their new star-making machinery. It works like this:
They fire off a beam of sodium laser light, just 4 watts, into the night sky right about where they are observing. When the sodium laser beam gets to about 60 miles up into the atmosphere it causes a tiny amount of sodium gas up there to glow --- just like a faint star. You can't even see it with the naked eye, it is that faint.
This convenient porta-star can be seen by the telescope, the AO system can correct for the distortion of the atmosphere, and --- ba-da-bing! --- it's almost like there isn't an atmosphere at all. Your images are sharp and information-filled, nearby star or not.
The whole system --- telescope, computers, and the new laser system --- should be working in unison by next year, breathing new life into the old and venerable Hale Telescope. It is indeed the Great Scope that just keeps getting better.
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2004.11.13 12:00 PM | Comments (0)
