A coronagraph blocks a star’s bright light to help directly image faint exoplanets.
In direct imaging, the host star can be billions of times brighter than a nearby planet, so the planet’s reflected or emitted light is easily lost in glare. A coronagraph uses masks, optical stops or phase-manipulating elements to suppress the central starlight while allowing light from nearby off-axis objects to reach the detector.
The concept was invented by French astronomer Bernard Lyot, who introduced the coronagraph in 1931 to observe the solar corona without waiting for a total eclipse. Modern stellar coronagraphs adapt that idea for exoplanets and circumstellar disks. Instruments on space telescopes such as Hubble and Webb include coronagraphic capability.
A coronagraph does not magnify an exoplanet or identify it through a spectrum alone. It reduces glare; adaptive optics, careful calibration and image processing are also crucial. A related technique, starshade occultation, blocks starlight with a separate spacecraft rather than an instrument inside the telescope.