Coronal holes
Encyclopedia
Coronal holes are areas where the Sun's corona
is darker, colder, and has lower-density plasma than average. These were found when X-ray
telescopes in the Skylab
mission were flown above the Earth's atmosphere to reveal the structure of the corona. Coronal holes are linked to unipolar concentrations of open magnetic field lines. During solar minimum
, coronal holes are mainly found at the Sun's polar regions, but they can be located anywhere on the sun during solar maximum
. The fast-moving component of the solar wind
is known to travel along open magnetic field lines that pass through coronal holes.
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
is darker, colder, and has lower-density plasma than average. These were found when X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
telescopes in the Skylab
Skylab
Skylab was a space station launched and operated by NASA, the space agency of the United States. Skylab orbited the Earth from 1973 to 1979, and included a workshop, a solar observatory, and other systems. It was launched unmanned by a modified Saturn V rocket, with a mass of...
mission were flown above the Earth's atmosphere to reveal the structure of the corona. Coronal holes are linked to unipolar concentrations of open magnetic field lines. During solar minimum
Solar minimum
Solar minimum is the period of least solar activity in the solar cycle of the sun. During this time, sunspot and solar flare activity diminishes, and often does not occur for days at a time...
, coronal holes are mainly found at the Sun's polar regions, but they can be located anywhere on the sun during solar maximum
Solar maximum
Solar maximum or solar max is the period of greatest solar activity in the solar cycle of the sun. During solar maximum, sunspots appear....
. The fast-moving component of the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
is known to travel along open magnetic field lines that pass through coronal holes.