Instrumentation

An instrument that blocks the overwhelming light of a star so the far fainter objects beside it — a planet, a disc, the solar corona — can be seen. First built by Bernard Lyot to study the Sun, it is now central to directly imaging exoplanets; SPHERE on the VLT is a modern example.

A thin mirror whose surface is reshaped hundreds or thousands of times a second by an array of actuators, cancelling the distortion the atmosphere imposes on starlight in real time. The active heart of adaptive optics — the ELT's M4 is one of the largest ever built.

A high-resolution spectrograph that uses a coarse, steeply-ruled grating (an échelle) to spread light into many overlapping orders, then a second disperser to separate them — packing very high spectral resolution onto a single detector. The workhorse of precision radial-velocity and stellar-abundance work; HIRES is a classic example.

A spectrograph that records a full spectrum at every point in a two-dimensional field of view at once, producing a 'data cube' of the sky — an image where every pixel is a spectrum. It maps how motion and composition vary across a galaxy or nebula in a single exposure; MUSE on the VLT is a leading example.

An artificial star created by shining a laser into the upper atmosphere, exciting sodium atoms ~90 km up to glow. It gives adaptive optics a bright reference point anywhere on the sky — not just near a real bright star — so the shape of the atmosphere's blur can be measured and corrected.

A concept for blocking a star's light not inside the instrument but far in front of the telescope — a large, precisely-shaped screen flown tens of thousands of kilometres away, casting a deep shadow so an orbiting planet stands clear. A proposed external alternative to the coronagraph for future exoplanet-imaging missions.

The eye of an adaptive-optics system — it measures, hundreds or thousands of times a second, exactly how the atmosphere has distorted the incoming light, so a correction can be computed and applied. Common designs are the Shack–Hartmann and pyramid sensors.