Extreme ultraviolet Imaging Telescope

EIT: a normal-incidence, multilayer telescope.

EIT images the solar transition region and the lower corona, ie the Suns lower atmosphere. It does this in ultraviolet light and uses four different ranges, corresponding to different temperature and density ranges. The different ranges correspond to filters made from different elements, the different filters and there uses are:

Element	Wavelength	Average Temperature	Used For
Helium (He II)	304 Angstroms	8,000 Kelvin	Observing the chromosphere (the very low solar atmosphere)
Iron (Fe IX-X)	171 Angstroms	1,300,000 Kelvin	Observing the corona and the transition region
Iron (Fe XII)	195 Angstroms	1,600,000 Kelvin	Observing the corona
Iron (Fe XV)	284 Angstroms	2,000,000 Kelvin	Observing hotter active parts of the corona

The number by the element in Roman Numerals identifies different types of the element. An Angstrom is 0.000,000,01 cm and Kelvin is a temperature scale which is the same as Celsius except it starts at -273 C.

Full Sun images taken on 18th June 98 in (top) He II, Fe IX-X and (bottom) Fe XII, Fe XV.

EIT can take images of the full Sun or can focus in on smaller regions. This allows it to study phenomena in the corona such as coronal loops (streams of hot dense plasma which loop out from the surface of the Sun) and prominences (dense plasma which is held above the surface of the Sun by magnetic forces, counteracting the effects of gravity).

These observations can be used to calculate temperature and density of the plasma in the corona. Above, Fe IX-X and Fe XII images, from 8th Dec 98, have been used to generate a temperature map. The lighter the colour, the hotter the plasma at that point. Here, the temperature ranges from 900,000 K to 1,500,000 K, but using different filter ranges gives different temperature ranges.
Note, the red squares indicate areas where data has been lost or corrupted for one reason or another.

Pictures and infomation courtesy of the SOHO EIT consortium.

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