Final answer:
The temperature of a star fluctuates throughout its life, initially increasing due to gravitational energy and nuclear fusion, eventually cooling as it exhausts its nuclear fuel and ends its life cycle. Contrary to this, the universe overall has cooled as it has expanded since the Big Bang.
Step-by-step explanation:
The temperature throughout the life of a star fluctuates. Initially, as a star forms from a cloud of gas and dust, gravitational energy converts to heat, raising the star's temperature. Once the star reaches the main sequence phase of its life, nuclear fusion in its core releases enormous amounts of energy, further increasing its temperature. Eventually, as the star exhausts its nuclear fuel, it may expand to become a red giant, where its core temperature rises while the outer layers cool. Finally, the star will shed its outer layers and end its life as a white dwarf, neutron star, or black hole, cooling over time. These stages show that a star's temperature does not remain constant but changes in response to various physical processes in its lifecycle.
Comparably, as it pertains to the universe, after the Big Bang, the temperature of the universe decreased as it expanded. This is in contrast to a star, whose temperature is dictated by different processes over its lifespan.