Glossary term: adaptive optics

Description: When you look up at night, you might see the stars twinkle. The air in the atmosphere is always in motion, and as light from a star passes through a region with turbulence, it gets deflected by a varying amount. That is why what we can see in the sky is not a single steady point of light for each star, but a dancing, ever-changing, distorted succession of points. For astronomers, twinkling means that they cannot take images of celestial objects in as much detail as their large ground-based telescopes would otherwise allow. Active optics is a way of mitigating that effect. Using either a real star or a laser-projected "artificial star", an adaptive optics ("AO") system monitors atmospheric distortion in real time. Light that has entered the telescope is guided onto a deformable mirror. Controlled by a computer, that mirror is deformed in just the right way to counteract atmospheric distortion.

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The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

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The planet beta Pictoris b is a bright dot close to its parent star. Around this we see a warm disk edge-on

beta Pictoris b

Caption: This composite of two images shows the planet beta Pictoris b and a disk of material both of which orbit the young star beta Pictoris. Both are taken in infrared light. The inner image was one of the first pictures taken of a planet around another star (an exoplanet). This image was made using a technique called adaptive optics which removes the blurring effect of the Earth's atmosphere that spreads out a star's light. The star's light is then concentrated tightly enough that it can be hidden behind a blocking circle (shown here in black) called a coronagraph. The ripples around this are artifacts of the imaging process. Beta Pictoris b, a gas giant planet about twelve times the mass of Jupiter, appears as a dot above and to the left of the black circle. The outer image shows the thermal emission from the warm disk of material surrounding the young star beta Pictoris. As we are viewing this disk edge-on it appears as a line. This disk of gas and dust provided the material to form beta Pictoris b.
Credit: ESO/A.-M. Lagrange et al. credit link
License: CC-BY-4.0 Creative Comments Attribution 4.0 International (CC BY 4.0) icons
The four telescope domes of VLT. One dome is open and firing laser beams. In the sky, the moon has a ring of light around it.

ESO's Very Large Telescope (VLT) at Paranal Observatory with a lunar halo

Caption: The Very Large Telescope on Cerro Paranal in Chile has four reflecting telescopes each with a primary mirror 8.2m across. In this image one dome is open and firing laser beams into the sky. These lasers create artificial stars in the sky that can be used to adjust the telescope optics to remove the blurring effect of the Earth's atmosphere. This process is known as adaptive optics. In the sky the Moon is surrounded by a bright halo. This is caused by light from the moon reflecting inside ice crystals in the Earth's atmosphere.
Credit: Juan Carlos Muñoz-Mateos/ESO
License: CC-BY-4.0 Creative Comments Attribution 4.0 International (CC BY 4.0) icons