Final answer:
A point of light moving quickly in the sky is not a star; it is more likely to be a meteor. To differentiate a star from a quasar, astronomers use spectroscopy to analyze luminosity, spectrum, and redshift. The general theory of relativity and atmospheric refraction can affect how we perceive star positions.
Step-by-step explanation:
If a point of light is moving in the sky, it cannot be a star, as stars do not move significantly relative to Earth over short periods like a single night. This is because even objects with significant motions of their own, such as nearby planets, appear almost stationary relative to the stars over a short time frame. Only meteors, which are actually small pieces of cosmic dust entering Earth's atmosphere, show noticeable movement across the sky in a short period.
The apparent position of a star can be affected by phenomena like atmospheric refraction, where the light from a star is bent as it passes through Earth's atmosphere, or by gravitational lensing as described by the general theory of relativity, which occurs when the star's light passes near a massive object like the Sun.
To determine whether a star-like object is a star or a quasar, astronomers would observe the object's properties such as luminosity, spectrum, and redshift. Spectroscopy can yield valuable information about the material within a star or quasar and its movement. For instance, colors in a galaxy's light can indicate the types of stars it contains, and the redshift of spectral lines can reveal the object's motion relative to Earth. These characteristics help astronomers to distinguish between stars, quasars, and other celestial objects.