Direct Imaging: Structures & Vocabulary

Direct imaging isolates photons from an exoplanet itself rather than inferring the planet only through its effect on the host star. The central challenge is contrast: a planet can be millions to billions of times fainter than a nearby star and separated by a tiny angle on the sky.

A coronagraph blocks or destructively suppresses the star's diffraction pattern while preserving off-axis planet light. Adaptive optics corrects atmospheric distortion for ground-based observations, and differential imaging separates stable instrumental speckles from real astrophysical companions.

Systems such as HR 8799 show multiple planets tracked over years of orbital motion. Infrared spectra and photometry of directly imaged worlds reveal temperatures, clouds, molecules, and surface gravity.

Imaging systems combine large apertures, adaptive optics, coronagraphs or starshades, wavefront control, and post-processing. Angular separation and contrast define the accessible planet space.