Sirius, the brightest star in the night sky, is in the south at nightfall. If you keep your eye on it for a few seconds, though, you’ll see that Sirius isn’t steady. It twinkles fiercely. It gets brighter and fainter, and it changes color rapidly — from red to blue to pure white.
The twinkling is beautiful — unless you’re an astronomer. Twinkling blurs and distorts the view of stars and other objects. That makes pictures of the universe look fuzzy — not good if you’re trying to see the smallest possible details. But astronomers have found a way to overcome the blur — a technique known as adaptive optics.
The stars twinkle as their light passes through different layers of the atmosphere. Air masses of different temperature and density “bend” and split the light. So starlight follows a bit of a zig-zaggy path through the air, making its source look blurry.
Adaptive optics uses a small, flexible mirror to compensate for the blurring. The system looks at a “guide star” — either a real star, or a fake one created by shining a laser beam high in the sky, causing certain atoms to glow. The mirror flexes to keep the guide star sharp. That keeps the images of the sky in sharp focus as well.
Adaptive optics has been around for more than two decades. Today, scientists and engineers are working on “next-generation” versions of the technology — overcoming the beautiful but annoying twinkling of the stars.