Before equipment and processing, six ideas make everything else click: what you photograph (nebulae, galaxies, clusters, supernova remnants), what light is (photons — discrete packets you collect over time), how color works (wavelength, and the narrow emission lines nebulae glow at), the core challenge (signal vs noise), why tracking is needed (Earth's rotation), and how a sensor records light (pixels counting electrons). Each sub-page below covers one.