Alpha centauri b is a star that is about the same size as the sun. why does it appear much smaller and dimmer than the sun when seen from earth?

Alpha Centauri B appears much smaller and dimmer than Sun, due to its greater distance from earth than Sun's and its lesser temperature than Sun, respectively.

Explanation:

Alpha Centauri B has a mass of 0.907 times the mass of Sun. But, its luminosity is less than that of the luminosity of Sun, because its temperature (5260 K) is less than that of the Sun (5778 K).

This, is the reason why Alpha Centauri B appears dimmer than the Sun.

The Sun is at a distance of 0.000015559 light years from earth, while Alpha Centauri B is at much larger distance of 4.37 light years from Earth.

Due, to this reason Alpha Centaurus B appears much smaller than the Sun from Earth.

the answer is:  

line graphs show patterns in data with variables that change over time; whereas, circle graphs show data as parts out of a whole (such as out of 100%).