Question
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 may appear smaller and dimmer than the Sun when seen from Earth due to its distance from us. Alpha Centauri B is located about 4.37 light-years away, which means it is over 25 trillion miles away.
Even though Alpha Centauri B is similar in size to the Sun, its distance makes it appear significantly smaller in the sky. This is known as angular size, and it is the apparent size of an object as seen from a particular vantage point. Since Alpha Centauri B is much farther away than the Sun, the angular size of the star when viewed from Earth is considerably smaller.
Additionally, the apparent brightness or dimness of a star is influenced by its luminosity and distance. While Alpha Centauri B has a similar size to the Sun, its brightness is lower since it has a lower luminosity. A star's luminosity refers to the total amount of energy it emits in all directions. Therefore, even though the star may have a similar physical size, the combination of its lower luminosity and greater distance results in it appearing both smaller and dimmer from Earth compared to the Sun.