Final answer:
In astronomy, the hotter star is the one with the higher temperature. The temperature determines the color and brightness of a star.
Step-by-step explanation:
In astronomy, the temperature and brightness of a star are related. A star's temperature determines the color of light it emits, and the hotter a star is, the brighter it appears. Therefore, if two stars have the same size but different temperatures, the hotter star will be the one with the higher temperature.
For example, if one star has a temperature of 8700 K and the other has a temperature of 2900 K, the star with a temperature of 8700 K will be brighter. The difference in brightness can be calculated using the Stefan-Boltzmann law, which states that the luminosity of a star is proportional to the fourth power of its temperature.