You cannot look at the sun without special filters, and the naked eye
cannot perceive certain wavelengths of sunlight. Solar physicists must
consequently rely on spacecraft that can observe this invisible light
before the atmosphere absorbs it.
“Certain wavelengths either do not make it through Earth’s atmosphere
or cannot be seen by our eyes, so we cannot use normal optical
telescopes to look at the spectrum,” said Dean Pesnell, the project
scientist for the Solar Dynamics Observatory, or SDO, at NASA’s Goddard
Space Flight Center in Greenbelt, Maryland.