Why are the SECCHI/EUVI images different colors and what do they mean?
All of the SECCHI/EUVI images are actually produced by extreme ultraviolet (EUV) light from the Sun. This is light that is between ultraviolet light and x-ray light in the electromagnetic spectrum and is not visible to our eyes directly. EUVI images are taken at four different wavelengths and four colors in order of wavelength (bluer=shorter wavelength, redder=longer) were assigned to represent each of them. Just as the human eye is capable of discriminating different colors in the visible, so EUVI’s four bandpasses discriminate among four “colors” in the extreme ultraviolet. In addition, each color table was carefully constructed to bring out typical features of its particular wavelength. The red images have a wavelength of 304 Angstroms, the yellow are 284 Angstroms, the green are 195 Angstroms, and the blue are 171 Angstroms. So, just like in the visible spectrum where red is the longest wavelength and blue is the shortest with yellow and green in between, the EUVI image colors were
