Direct imaging

Direct imaging is an observational technique that detects a faint astronomical object separately from the light of a nearby bright source, often a star. It uses high-contrast instruments and image processing to suppress or distinguish the source’s glare.

Coronagraph: An optical instrument that blocks or redirects light from a bright source to reveal nearby faint objects. It suppresses starlight before it overwhelms the signal from a companion object.
Exoplanet: A planet that orbits a star other than the Sun. Direct imaging provides spatially separated observations of some exoplanets.
Radial velocity method: An exoplanet detection method that infers a planet from periodic shifts in its star’s spectral lines. It detects a planet through its gravitational effect rather than separating its light from the star.
Angular resolution: The smallest angular separation at which an imaging system can distinguish two sources. A planet must be separated enough from its star to occupy distinguishable image structure.
Hubble Space Telescope: A space observatory launched in 1990 that observes across ultraviolet, visible, and near-infrared wavelengths. Its coronagraphic observations have imaged disks and faint companions near stars.
Adaptive optics: A system that corrects image distortion in real time by adjusting a telescope’s optical elements. Sharper images concentrate starlight and make nearby faint signals easier to distinguish.
HR 8799: A young star whose directly imaged planetary system includes four massive planets. Its planets are a landmark example of multiple companions detected in direct images.
Transit method: An exoplanet detection method that measures periodic dips in a star’s brightness as a planet crosses its face. It usually reveals a planet through changing brightness, not a resolved planetary image.
Strehl ratio: A measure comparing an image’s peak intensity with that of an ideal diffraction-limited image. A high Strehl ratio indicates that adaptive optics has concentrated light into a sharp image.
Gemini Planet Imager: A high-contrast imaging instrument on the Gemini South Telescope, designed to observe young giant planets. It combined adaptive optics, a coronagraph, and an integral-field spectrograph for planet imaging.

Linked from 10 pages