Is a star a ball of gas?
Stars are composed of plasma, which is matter in a state similar to gas. The difference is that some -- not all -- of the particles in plasma are ionized, or made to lose a certain number of their electrons. This allows plasma to have different properties than solids, liquids, or gasses, while retaining some aspects of all three. For example, the Sun is composed of hydrogen and helium in a partially-ionized state, allowing fusion to take place; the sun is a fluid object (liquid) in a contained state (solid), and contains and releases a great deal of particulate matter (gas). Fusion allows the Sun to continue emitting radiation on all spectrums and wavelengths, giving off the heat and light that keeps the Earth viable for life. Stars in general are composed of plasma in a constant state of fusion until the ratio of heavy metals -- a byproduct of fusion -- to plasma reaches a certain point, at which the star begins to collapse on itself.
Yes it is.
♦ Star (astronomy), massive shining sphere of hot gas. Of all the stars in the universe, our Sun is the nearest to Earth and the most extensively studied. The stars visible to the naked eye all belong to the Milky Way Galaxy, the massive ensemble of stars that contains our solar system (the Sun and its nine planets).
♦ All stars are composed of hot glowing gas. The outer layers of some stars are so empty that they can be described as red-hot vacuums. Other stars are so dense that a teaspoonful of the material composing the outer layers would weigh several tons.
♦ Stars are made chiefly of hydrogen and a smaller amount of helium. Even the most abundant of the other elements present in stars—oxygen, carbon, neon, and nitrogen—are generally present in very small quantities.