Its famous in astronomy. A telescope on the ground will never be able to achieve the same results than the same one in space. Why? Because of the atmosphere. The atmosphere has always been astronomers’ worst enemy, for several reasons:

1. Turbulances
2. Shifts in Temperature
3. It blocks certain wavelengths (Ultraviolet), which are valuable to astronomers
4. Water Vapour deteriorates visibility
5. Objects low on the horizon are blurry
6. And many more reasons…

Even though both will never match, we will continue developping Ground Based Telescopes, mostly because of the differences in budget. The Hubble Space Telescope cost several billions of dollars, while the Very Large Telescope (VLT) project by the European Southern Observatory (ESO) only cost a few millions of dollars. Hubble’s mirror diameter is 2.4 m, while the VLT is composed of 4 Telescopes, each with a mirror of over 8 meters in diameter! But Hubble does match the VLT… Not for long (maybe). Scientific Equipment Opticians around the world are working around a revolutionary concept for grown based telescopes, called Adaptive Optics

What these little jewels do is fairly simple. They Calculate the movement of air turbulences and light distortions above the telescope, and, using a mirror that can be moved, act on it, move it, and twist it, so that it compensates exactly the distortions. The twisting of the mirror, of course, is on a tiny scale (nanometers). The technology was first applied on telescopes in the 1990s, and the system is getting better day by day. Today, these systems can calculate and act on the telescope’s mirror up to a million times a second! Gee… That’s a lot! I met one of those scientific opticians one day, who had also worked on the Rosetta mission, called Kjetil Dohlen, and he helped clarify how they worked. He was working on the Adaptive Optics set on the VLT telescopes.

You must not mix adaptive optics with active optics. Active Optics are used when a telescope’s mirror is deformed under its own weight, and little mechanisms placed behind it compensate the gradual distortion of the mirror.

Even though adaptive optics can’t correct everything wrong with the atmosphere, they definitely help astronomers getting the most out of their Ground Based Telescopes