Apparent brightness is the measure of how bright a star or celestial object appears to an observer on Earth, influenced by both its intrinsic luminosity and its distance from the observer. It is a crucial factor in astronomical observations, helping astronomers determine the properties of stars and galaxies by accounting for the effects of distance and interstellar medium on observed light.
Spectroscopy is a scientific technique used to analyze the interaction between matter and electromagnetic radiation to determine the composition, structure, and properties of substances. It is fundamental in fields like chemistry, physics, and astronomy for identifying materials and understanding molecular and atomic interactions.