I'm sure you've enjoyed plenty of starry nights, and if you haven't you really ought to sometime soon. There's nothing like staring up thousands of glittering points of light, contemplating the vastness and complexity of it all. It really puts everything in perspective.
One of the best parts of a nice dark sky is getting to see the twinkle of the starlight. It's almost as if the stars are alive, wiggling back and forth in place, trying to tell you the deepest secrets of the universe.
That twinkling is caused by our atmosphere. Our air is constantly in motion, with warm and cold layers fighting for dominance. It’s just constant turmoil from ground level to a hundred miles up. As light from those distant points makes its through all that turbulence, the light gets shifted back and forth, causing the characteristic twinkle.
(As a side note, this is why the planets themselves don't twinkle. Not because they're brighter, but because they're close enough to be solid disks rather than single points of light. While they're like to experience the same turbulence as the starlight, it all just gets mixed up within that same disk and so you don't get any twinkle.)
To an astronomer, that beautiful twinkling starlight is one of the most aggravating things in the universe.
I mean, come on, we're trying to do science and get as precise measurements as possible. If those stars would just stop wiggling for one second we can get a lot better data.
To solve for this astronomers have three basic approaches:
- Build telescopes really high up in really arid environments, so that there's as little atmosphere between us and the stars as possible, and that air is as calm as possible to minimize twinkle.
- Skip the atmosphere altogether and just put our telescopes up in space. No air, no twinkle. Pure science. But also kind of pricey.
- Shoot a really bright laser up into the sky and watch it wiggle back and forth as it passes through the shifting layers of the atmosphere. Attach motors to the mirror of your telescope to compensate for that motion that you observe in the laser.
The last approach is called adaptive optics it is the latest technique for dealing with your pesky atmosphere.
It’s the adaptive optics approach that allows us to build giant ground-based observatories. Without it, the telescopes would be useless. Sure, we'd have bigger mirrors, but we would be limited in our precision by the twinkle of the stars themselves. But thanks to this new technique we can enter an era of new mega-telescopes far larger than astronomers of past generations would have even thought possible.