In this series, we explore the weird and wonderful world of astronomy jargon! Match your glasses to read about today’s topic: adaptive optics!
Let’s say you are an astronomer. You have built a gigantic new observatory to study the sky above you. You look through the eyepiece (or more precisely the computer screen) and expect the glory of space to be revealed to you. Instead, all you will find is a blurry, shaky mess to your frustration.
Earth’s atmosphere is pretty good when it comes to keeping living things alive, but pretty terrible when it comes to astronomy. No matter how big your telescope is, how sophisticated, and how powerful it is, as long as it’s on the ground, it has to deal with all these miles of atmosphere.
The problem is the ever-changing turbulent movements of hot and cold air, which struggle to distribute heat evenly across the globe. Warm and cold air have different indices of refraction, which means that they bend the light path differently. The light of a distant star does not follow a straight line on its way through our atmosphere – it is constantly shifting, zigzagging and zigzagging as the air moves.
It is exactly the same process that makes stars sparkle. It’s pretty, but annoying.
Sure, you can mitigate some of this by building your observatory in a desert (to keep the air as calm as possible) and / or on a mountain (to minimize the amount of air between you and space), but you can’t Get rid of.
You could just launch your observatory into space, but rockets are only so big and launches are so darn expensive that it is much cheaper to leave your huge observatory on the ground.
The solution? Break out the lasers and do some adaptive optics.
Shoot a bright laser into the sky. Watch it dance due to the same atmospheric distortions that mess up your observations. Glue the mirror of your telescope onto an adjustable table. As the laser shifts, move your mirror with it to cancel out the effects of the turbulent atmosphere.
It’s a simple idea, but very difficult to put into practice. One of the origins of the development of the technology was secret research by the US military to better track enemy satellites. It wasn’t until the 1990s that the technology was mature enough to make it a mainstay of modern astronomy.