Background Information
A similar effect occurs if a star or galaxy is moving relative to Earth. When a star approaches Earth, the light waves it emits are compressed, causing its light to be shifted toward the blue end of the spectrum. This is called blueshift. When a star moves away from Earth, its light is shifted toward the red end of the spectrum, a phenomenon called redshift.
In 1912, an astronomer named Henrietta Swan Leavitt studied a class of stars called Cepheids. These stars change from bright to dim to bright again. Her discoveries led to a method of measuring distances to other galaxies and eventually helped to support the Big Bang theory of the origin of the universe.
Stars emit light at a variety of wavelengths. Just as white light is separated into a rainbow when it passes through a prism, starlight can be separated into its constituent colors when it passes through an instrument called a spectrograph. The result is a pattern of colors and black bars called an absorption spectrum. The bars represent wavelengths of light that are absorbed in the star’s atmosphere. Each star’s unique spectrum depends on the temperature and composition of its atmosphere.
This is the spectrum of star A-091. Each star has a unique spectrum, just like every human has unique fingerprint. Notice the dark lines.
