This is a device that can precisely measure the wavelength of light, and can for example distinguish light emitted by a hydrogen atom from light emitted by helium.
Many telescopes are designed to primarily capture visible light, which represents only a sliver of the spectrum of light emitted by stars and other celestial objects.
Although this is slower than the speed of the light and materials emitted by solar flares, coronal mass ejections can have much more dramatic effects on Earth.