A coronagraph is an astronomical instrument, typically attached to a telescope, that uses an internal occulting disk or mask to block the direct light of a bright object, most commonly the Sun or a nearby star, so that much fainter structures around it, such as the solar corona or a planet orbiting a distant star, become visible against the glare that would otherwise overwhelm them. The instrument was invented in 1930 by the French astronomer Bernard Lyot, whose coronagraph allowed the solar corona to be observed and studied on ordinary clear days for the first time, rather than only during the brief minutes of a total solar eclipse. Coronagraphs remain central to solar physics research, mounted on both ground-based observatories and dedicated spacecraft, and modern high-contrast coronagraphs adapted for nighttime astronomy are now a key tool in the direct imaging and study of exoplanets orbiting other stars.
Facts
Invented Year Measuresfaint objects, such as the solar corona or a star's circumstellar disk, that are otherwise hidden in the glare of a much brighter nearby object 1 Operating PrincipleAn occulting disk or mask placed at a focal plane blocks the direct light of the bright central object, while an arrangement of lenses, stops (Lyot stops) and baffles absorbs the light scattered by diffraction, so only the much fainter surrounding light reaches the detector. 1 Operating Rangemust reject stray light down to roughly one millionth of the brightness of the object it blocks, since the solar corona is less than a millionth as bright as the Sun's disk 1 Classification
Instrument Class Connections
Used In
The coronagraph blocks a bright source's direct light to reveal faint structure around it, invented by Bernard Lyot in 1930 to observe the solar corona without an eclipse, and used in astrophysics for exoplanet and stellar-envelope imaging.
Sources
1. Coronagraph (Wikipedia)
WikipediaWikipedia, Coronagraph article, Invention section, first sentence
The coronagraph was introduced in 1931 by the French astronomer Bernard Lyot; since then, coronagraphs have been used at many solar observatories.
Wikipedia, Coronagraph article, lead section, first sentence
A coronagraph is a telescopic attachment designed to block out the direct light from a star or other bright object so that nearby objects, which otherwise would be hidden in the object's bright glare, can be resolved.
Wikipedia, Coronagraph article, Design section, describing Lyot stops
Lyot's key invention was an arrangement of lenses with stops, known as Lyot stops, and baffles such that light scattered by diffraction was focused on the stops and baffles, where it could be absorbed, while light needed for a useful image missed them.
Wikipedia, Coronagraph article, Design section, contrast ratio figure
Coronagraph instruments are extreme examples of stray light rejection and precise photometry because the total brightness of the solar corona is less than one millionth that of the Sun's disk.
Lede, instrument class
A coronagraph is an astronomical instrument, typically attached to a telescope, that uses an internal occulting disk or mask to block the direct light of a bright object, most commonly the Sun or a nearby star, so that much fainter structures around it, such as the solar corona or a planet orbiting a distant star, become visible against the glare that would otherwise overwhelm them.
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