The coronagraph, an instrument used in space observatories, is an essential tool in the study of the Sun's outer atmosphere, or corona. It provides detailed images of the corona by blocking the Sun's bright disk, thus enabling scientists to observe the much fainter emissions from the corona. The understanding of the corona is of significant importance as it plays a crucial role in space weather, which affects not only the Earth's environment but also satellites and astronauts in space.
One of the earliest pioneers of the coronagraph was French astronomer Bernard Lyot in the 1930s. Lyot's invention allowed scientists to observe the Sun's corona without having to wait for a total solar eclipse. The coronagraph has since evolved and improved, with modern versions now being used in space, free from the distortions caused by Earth's atmosphere.
Currently, the Large Angle and Spectrometric Coronagraph (LASCO) on the SOHO (Solar and Heliospheric Observatory) spacecraft, a project of international collaboration between the European Space Agency and NASA, is one of the most well-known coronagraphs. LASCO has been observing the Sun since 1995, providing valuable data about the structure and flow of the solar wind, as well as the mass ejections from the Sun.
Another notable coronagraph is the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. This instrument has been used to observe planets, comets, and the interstellar medium. It has also been utilized to study the atmospheres of exoplanets by observing them as they pass in front of their host stars - a process known as a transit.
Looking ahead, the future of coronagraph research is promising. The planned NASA's Solar Probe Plus mission, set to launch in 2025, will carry a coronagraph that will get closer to the Sun than any previous mission. This proximity will allow the coronagraph to capture unprecedented images of the Sun's corona, providing new insights into solar physics and space weather.
In summary, the coronagraph is an indispensable instrument in the field of solar physics, providing crucial insights into the Sun's corona and its effects on space weather. Its evolution from Lyot's original design to its modern usage in space observatories exemplifies the progress in our quest to understand the Sun and its impact on our solar system.