Imagine that the Sun went out. It is only a pretend question. The Sun will not suddenly disappear, and scientists have no reason to expect it. As of November 2026, the Sun has been shining for billions of years. It will keep shining for about 5 billion more years. In about 5 billion years it will swell into a red giant.

The Sun is a star, the star at the center of our solar system. It is a giant, glowing ball of hot gas. Its middle is so hot and so squeezed by gravity that hydrogen atoms meld into helium. This is nuclear fusion, and it makes the Sun's heat and light. Light from the Sun takes about 8 minutes to reach Earth. So we always see the Sun as it was about 8 minutes ago.

The Sun is far away, about 93 million miles (150 million kilometers) from Earth, as of November 2026. Pluto is about 40 times as far from the Sun as Earth is, and it is extremely cold: about 230 degrees Celsius below zero. A light-year is the distance light travels in one year. It is about 6 trillion miles (9.5 trillion kilometers).

The nearest star to our Sun is Proxima Centauri, about 4.24 light-years away, as of November 2026. The Sun is one star among 100 billion or more in our galaxy, the Milky Way. Astronomers estimate the universe could hold up to one septillion stars, a 1 followed by 24 zeros. The Sun is much bigger than any planet. It would take almost 1,000 Jupiters to fill it up.

The Sun gives Earth its light and its warmth. Its gravity pulls on Earth and the other planets and keeps them circling around it. Earth is the third planet from the Sun. Plants use the energy in sunlight to make their food. This is called photosynthesis. The Moon does not make its own light. It shines because sunlight lights up and reflects off its surface.

Sunlight reaches only the top of the ocean. Below about 1,000 meters the ocean is completely dark. Yet deep in the dark ocean, hot springs called hydrothermal vents have living things that do not depend on sunlight. At vents, tiny bacteria use chemicals from the vent water for energy instead of sunlight. This is called chemosynthesis. These bacteria are the base of the vent food web.

Words to know

• fusion: joining together
• septillion: a huge number
• chemosynthesis: food from chemicals
• bacteria: tiny living things
• hydrothermal: hot water