Final answer:
An artificial star is a point of light in Earth's atmosphere created by a laser, used for monitoring atmospheric fluctuations and assisting in the calibration of telescope optics.
Step-by-step explanation:
An artificial star is A) a point of light in Earth's atmosphere created by a laser for the purpose of monitoring atmospheric fluctuations. This technology is often used in astronomy to fine-tune the optics of telescopes and to compensate for the effects of atmospheric distortion, enabling clearer images of celestial bodies. An artificial star does not inherently possess luminosity like an actual star, but its apparent brightness can be utilized in telescope calibration due to created laser light that simulates characteristics of starlight.
Astronomers also study the apparent brightness of stars, which refers to the energy emitted by a star that reaches a given area on Earth's surface. The vast majority of stars have such dim light that their apparent brightness is too low for the human eye to detect without the aid of telescopes.