 "Check pictures: How moon blocks the sun during a total solar eclipse")
A total eclipse occurs when the Moon passes in front of the Sun, blocking its bright disk and casting a deep shadow on to the Earth. The Moon's diameter appears to be the same size as that of the sun, blocking its light.
Northern Chile is known for clear skies and some of the largest, most powerful telescopes on Earth are being built in the area, turning the South American country into a global astronomical hub.
Over the course of a few hours, the shadow zooms across Earth’s surface at very high speed. The “path of totality” – the course that the shadow follows – is so large, it spans oceans and continents.
Thousands of tourists turn up to see the eclipse, along with a few dozen scientists, for which the eclipse is a unique opportunity to observe the extended atmosphere of the sun – known as the solar corona.
As the moon covers the bright disk of the sun, the surrounding atmosphere appears as a faint ring, with extended rays that point outwards from the sun like a crown – hence the name corona.
To observe the sun safely and study the corona during an eclipse, you need the special filters in a spectrometer. The spectrometer accepts light from the solar corona along a long, narrow entrance slit and during the eclipse. This slit scans to observe the whole corona.
Just like Earth, the sun has an atmosphere and magnetic field which extends out to large distances into space. The solar corona is an intense plasma of separated protons and electrons whose temperature reaches a million degrees Celsius or even more.