Cancelling out blur from Earth’s atmosphere lets astronomers focus like never before
ESO, P. Weilbacher/AIP, NASA, ESA, M.H. Wong and J. Tollefson/UC Berkeley
A telescope on Earth has snapped pictures of Neptune at least as clear as those from the Hubble Space Telescope. The trick? Taking the twinkle out of stars.
Released by the European Southern Observatory on July 18, the images come from a new observing system on the Very Large Telescope in Chile. The instrument uses four lasers to cancel out blurring caused by Earth’s atmosphere — the same effect that makes it look like stars are twinkling — at different altitudes.
The system is an updated version of adaptive optics (SN: 6/14/03, p. 373), a technique astronomers have long used to focus telescopes. Lasers create artificial “stars” whose size and brightness are precisely known. That gives scientists a way to measure how the atmosphere is distorting their view of real, faraway stars at any given moment. Small motors then change the shape of the telescope’s mirror in real time to correct for that distortion and see the sky as it really is.
The resulting images from the Chilean telescope are as sharp and clear as those taken from space. That’s good news, as Hubble won’t last forever, and planned future space telescopes won’t take images in the visible part of the light spectrum (SN: 3/17/18, p. 4). With adaptive optics, telescopes on the ground can pick up where Hubble leaves off.