Short answers, pulled from the story.
Astronomers observed a solar eclipse using early optical filters on the 12th of May 1706. This event marked one of the first documented uses of filtering technology in astronomy.
Modern solar filters must transmit only 0.00001% of incoming sunlight to ensure observer safety. These materials block harmful radiation while allowing safe viewing of the darkened sun during celestial alignment.
Small filters threaded behind eyepieces often fail under intense heat and can shatter unexpectedly due to thermal shock. They allow significant heating inside the telescope body which causes catastrophic failure and poses serious risks including retinal damage within seconds.
H-alpha filters transmit specific spectral lines for viewing solar flares invisible through common equipment. Some professional models pass only 0.05 nanometers versus several nanometers used elsewhere.
Emission nebulae radiate doubly ionized oxygen near 500 nanometers wavelength in the visible spectrum. These objects also emit weakly at 486 nanometers via the Hydrogen-beta line.