Final answer:
The spectrum of a star can reveal its temperature, chemical composition, size, and other characteristics. Color is a measure of a star's temperature. Stars are mostly made of hydrogen and helium, and Annie Cannon contributed to the understanding of stellar spectra through her classification system.
Step-by-step explanation:
When analyzing the spectrum of a star, we can learn about its temperature, chemical composition, atmospheric pressure, size, motion, and rotation. The spectrum of a star can provide valuable information about its characteristics. Color is a measure of a star's temperature because hot stars emit more blue light and cool stars emit more red light. Therefore, by observing the color of a star, we can estimate its temperature. The spectra of stars are not identical because they have different chemical compositions. Stars are mostly made of hydrogen and helium, and we know this because their spectra contain absorption lines corresponding to these elements.
Annie Cannon made significant contributions to the understanding of stellar spectra by developing a classification system known as the Harvard Spectral Classification System. This system categorizes stars based on the absorption lines present in their spectra. Characteristics of a star that can be determined by measuring its spectrum include its temperature, chemical composition, atmospheric pressure, size, and rotational velocity. By analyzing the absorption and emission lines in the spectrum, astronomers can extract information about these characteristics.