Final answer:
Stars each have a unique spectrum largely dictated by temperature, which impacts their spectral lines and color indications. Stellar spectroscopy enables astronomers to analyze aspects like chemical composition, pressure, size, and motion relative to Earth. Differences in the spectrum aid in classifying stars as main-sequence, giants, or supergiants.
Step-by-step explanation:
Every star having a unique spectrum suggests that while stars may have nearly the same composition as the Sun, they differ primarily due to their temperatures, which affect their spectral lines. The color of a star also serves as an indicator of its temperature, with blue stars being the hottest and red stars the coolest. Stellar spectroscopy allows astronomers to determine not only the temperature but also the detailed chemical composition, pressure in a star's atmosphere, size, and its motion toward or away from us. For instance, a distant G2 star with a spectrum matching the Sun is likely a main-sequence star with similar luminosity. Differences in spectrum could imply a star is a giant or supergiant, with giant stars having lower pressures than main-sequence stars, and supergiants even lower pressures than giants.