Computing and telescopes at the frontiers of optical astronomy

recording and understanding the stars and planets back thousands of years. But it was not until the early 17th century with the telescope’s invention that we recorded the first astronomical “images,” hand drawings of our Moon’s surfaces, the Sun, Venus, and Saturn, and Jupiter’s satellites. Detailed drawings by Galileo Galilei and others surpassed anything previously seen and were pivotal in advancing the Copernican hypothesis that our Sun—rather than the Earth—was the center of all motion. This revolutionized our perspective of the heavens and planted a seed of curiosity about the existence of other Earth-like places. Early astronomers quickly realized that bigger is better when it came to telescopes. Larger telescopes provide better sensitivity and resolution—they let us see fainter and smaller objects. But although astronomical imaging systems’ sensitivity improved steadily since Galileo’s time, only during the second half of the 20th century did we start to achieve some of the expected resolution increases. The problem is that the Earth’s atmosphere has pressure and temperature variations that lead to refractive-index changes along the light path from a star to a telescope. This atmospheric turbulence causes received signal intensity (scintillation) and phase fluctuations (aberrations), which produce blurred images. The wind’s impinging on the telescope causes additional image blur and gets worse as a telescope’s size increases. Without any correction for these image-blurring sources, we can’t get images with any better resolution—no matter how large a telescope is— than Isaac Newton and his 10-cm reflector telescope obtained. Figure 1 shows the components and light path that make up a Cassegrain reflecting telescope. Today, atmospheric turbulence and unwanted telescope motion are much less limiting factors to obtaining sharp imagery. Sophisticated adaptive-optics (AO) systems provide real-time wave-front compensation that makes the distorted light a telescope receives resemble what it looks like outside Earth’s atmosphere, and