Final answer:
A standard candle is an astronomical object with a specific known intrinsic luminosity, used by astronomers to measure cosmic distances based on its observed flux from Earth.
Step-by-step explanation:
A standard candle in astrophysics is an astronomical object that has a known intrinsic luminosity. This luminosity is a key property, as it does not change regardless of the object's location in the universe. Consequently, by measuring the observed flux or apparent brightness of the light reaching Earth, astronomers can effectively calculate the distance to these objects. Since intrinsic luminosity is a fixed value but observed flux varies with distance, standard candles serve as cosmic yardsticks. An example of such an object is a type Ia supernova, which has a consistent peak intrinsic luminosity, allowing for the determination of its distance from Earth based on how bright it appears.
Understanding the concept of standard candles is analogous to using a light bulb's luminosity to gauge distance in a dark room: if you know the light output, then comparing the apparent brightness lets you infer distance. However, not all stars or galaxies have the same luminosity, thus finding true standard candles is important for measuring vast cosmic distances.