Final answer:
Stars are objects in space made of gas that give off light and heat energy. The Sun is an example of a star that can be seen during the day and indirectly at night through reflected light from other objects.
Step-by-step explanation:
The object in space that is made of gas and gives off light and heat energy, and can only be seen at night, is a star.
Stars are enormous balls of glowing gas that generate vast amounts of energy by nuclear reactions deep within them. Unlike planets, which are visible primarily by reflected light, stars glow because of nuclear fusion. They appear faint because they are very far away from us.
For example, our local star, the Sun, is a star that is relatively close to us. It illuminates the Earth during the day and can be seen indirectly by reflected light from other objects at night.