What is a self-illuminated gaseous body of great size that produces its own energy by nuclear fusion called?

A self-illuminated gaseous body of great size that produces its own energy through nuclear fusion is known as a star. Stars, such as our Sun, are primarily composed of hydrogen and helium gases, and they generate energy in their cores through the process of nuclear fusion. This process involves the fusion of hydrogen atoms into helium, releasing an immense amount of energy in the form of light and heat, which is what makes stars visible in the night sky.

In contrast, comets, planets, and nebulae do not produce their own energy through nuclear fusion. Comets are icy bodies that originate from the outer regions of the solar system and produce visible comas and tails when they approach the Sun due to sublimation. Planets are celestial bodies that orbit stars, are made primarily of rock or gas, and do not generate their own light or energy. Nebulae are clouds of gas and dust in space, often the remnants of stellar explosions or the regions where new stars are forming, but they do not produce energy in the same way stars do. Therefore, the defining characteristics of a star make it the correct answer.