Online Astronomy eText: The Sun
Extreme Ultraviolet Images of the Sun Link for sharing this page on Facebook
Explanation of the colors used for SOHO extreme ultraviolet images of the Sun (that is, at wavelengths much shorter than "normal" ultraviolet wavelengths). Such radiation is also sometimes referred to as "soft" X-rays, since the boundary between X-rays and UV is rather arbitrarily set at about 100 Ångstroms. All the images shown above were taken on July 19, 2006 at wavelengths ten times shorter than the shortest visible wavelengths, imaging photons with ten times more energy than the most energetic visible photons. Since in the visible spectrum shorter wavelengths correspond to blue and green light, and longer wavelengths to yellow, orange and red light, the shorter wavelength images are arbitrarily colored blue or green, and the longer wavelength images are colored amber or red. The atoms (or more accurately, since the atoms are missing one or more electrons, the ions) responsible for the wavelengths involved are indicated by Roman numerals which are one unit greater than the number of missing electrons. So He II means helium ions which are missing one electron, and Fe XV means iron atoms which are missing fourteen electrons. The He II image looks different from the others because it shows radiation from moderately hot helium atoms in the chromosphere; while the highly ionized iron atoms responsible for the other emissions are located in the lower corona. (SOHO, ESA, NASA, EIT)

Example of SOHO extreme UV imaging, from April 7, 2006

Two eruptive prominences viewed in ultraviolet radiation. Taken March 21, 2003. (apod030418)

SOHO ultraviolet image of the Sun near solar maximum, taken on February 12, 2001. (apod010301)

Taken January 13, 2001. (apod010120)

Another eruptive prominence,
mid-September, 1999. (apod990923)
As indicated by the (arbitrarily assigned) reddish color, all four images were captured using the 304 Ångstrom radiation of ionized helium atoms in the solar chromosphere. (SOHO - EIT Consortium, ESA, NASA) (Click on the thumbnails for larger versions of the images.)

Coronal holes photographed by SOHO in extreme ultraviolet radiation on March 9, 2003.
(SOHO - EIT Consortium, ESA, NASA, apod030318)

Composite photo showing the Sun in three extreme ultraviolet wavelengths.
Blue represents 171 Ångstroms, green 195 Ångstroms, and red 284 Ångstroms.
(SOHO - EIT Consortium, ESA, NASA )

An extreme ultraviolet view of the Sun,
September 22, 2001. (apod010929)

An extreme ultraviolet view of the Sun,
March 20, 2002. (apod020321)
The radiation viewed in these images is emitted by 11-times ionized iron atoms with a temperature of about 1.5 million Kelvins (about 3 million Fahrenheit degrees). (SOHO - EIT Consortium, ESA, NASA ) (Click on the thumbnails for larger versions of the images.)