"Photometric Measurements of Variable Stars as a Tool to Determine Astronomical Distances."
Abstract: A period-luminosity relationship for variable stars exists which makes it possible to find distances to remote regions of the universe. By studying a variable star located within a distant object such as another galaxy and determining the period by which its apparent brightness changes, it is possible to obtain a reasonable estimate for its luminosity, or actual power output. From these two quantities of stellar luminosity and apparent brightness, a distance can be calculated by using the inverse-square law that the apparent brightness of a star as seen on Earth is proportional to the staršs luminosity and inversely proportional to the square of its distance.
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