One of the most important scientific advances of the space age is the discovery of coronal mass ejections. Called coronal mass ejections (CMEs) because the material in the ejection originates in the corona, CMEs are powerful eruptions in which as much as ten billion tons of plasma from the Sun’s atmosphere is blown into interplanetary space at one time. Traveling outward from the Sun and heading towards Earth at speeds up to 2000 kilometers per second, CMEs can create major disturbances in the interplanetary medium and trigger severe magnetic storms on Earth. CMEs are responsible for enhanced auroral activity, satellite damage, and power station failures by driving interplanetary shock waves and accelerating particles to relativistic speeds, all of which come crashing into the Earth’s magnetic environment.
Despite the importance of CMEs, their origin and evolution are still not well understood, and no one has a clear idea of their structure. While CMEs are routinely observed on the Sun with near Earth telescopes, those CMEs directed toward the Earth are the ones least likely to be detected. Thus, these solar eruptions pose a challenge for science.
To enable scientists in solving some of the most perplexing riddles about the Sun, including the internal structure of the Sun, the heating of its extensive outer atmosphere, and the origin of the solar wind, the Solar and Heliospheric Observatory (SOHO) was launched by an Atlas-Centaur rocket on December 2, 1995, and is one of the most ambitious space study missions to date. SOHO is a joint international space mission carried out by the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA). It is a
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sophisticated array of twelve scientific instruments developed by European and American scientists.
Large ground based radio dishes around the world are used to track the spacecraft beyond Earth’s orbit. Mission control is based at Goddard Space Flight Center in Maryland. SOHO’s uninterrupted view of the Sun provides solar data 24 hours a day. At no time is the Sun hidden from SOHO by the Earth. This is achieved by positioning SOHO at a point 1.6 million kilometers sunward of the Earth where the gravitational pulls of the Earth and Sun are in balance. This position is called L1 Lagrangian point and lies on the direct line between the Earth and the Sun, which allows SOHO to travel with the Earth as it revolves around the Sun at a distance 1.6 million kilometers closer to the Sun.
The LASCO, Large Angle Spectrometric Coronograph, instrument is one of the twelve instruments included on the SOHO spacecraft. The LASCO instrument is a set of three coronographs that image the solar corona. A coronograph is a telescope that is designed to block light coming from the Sun, in order to make the extremely faint emissions from the region around the Sun, known as the corona, visible. The essential questions to be addressed by LASCO deal with how the corona is heated, where and how solar wind is accelerated, what causes coronal mass ejections and other coronal eruptions, and what role does all of this play in the evolution of large scale coronal patterns.
For additional resources about SOHO and sample lesson plans on CMEs, visit this site:
- http://sohowww.nascom.nasa.gov/
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