Here is a pretend question: what if the Sun went out? Scientists have no reason to expect the Sun to suddenly disappear, so this is only a thought experiment, a way of imagining something to learn from it. As of November 2026, the Sun has been shining for billions of years, and it will keep shining for about 5 billion more years. Imagining it gone is a good way to see how much we get from it every day, because the Sun gives Earth its light and its warmth, and a great deal more besides.

The Sun is a star. It is the star at the center of our solar system, and it is a giant, glowing ball of hot gas. It is much bigger than any planet: it would take almost 1,000 Jupiters to fill it up, and about 1.3 million Earths to fill its volume. It also holds 99.8% of the solar system's mass, and it would take more than 330,000 Earths to match the Sun's mass. Earth is the third planet from the Sun.

The Sun is about 93 million miles (150 million kilometers) from Earth, as of November 2026. Light from the Sun takes about 8 minutes to cross that gap, which is why we always see the Sun as it was about 8 minutes ago. Farther out, sunlight takes about 5.5 hours to reach Pluto. Even there, the Sun looks about 300 times brighter than our full Moon. Distances in space are so large that scientists measure them in light-years, and a light-year is the distance light travels in one year: about 6 trillion miles (9.5 trillion kilometers).

Sunlight does much more than light up the day. The Sun's energy heats Earth's surface and air, powers ocean currents, drives photosynthesis and evaporation, and melts snow and ice. As of November 2026, Earth's average surface temperature is about 15 degrees Celsius (59 degrees Fahrenheit). The amount of energy involved is huge: every 1.5 millionths of a second, the Sun releases more energy than all humans use in an entire year. Earth is the only planet in our solar system with liquid water on its surface.

Plants use the energy in sunlight to make their food. This is called photosynthesis. Plants take in sunlight, and photosynthesis is how they turn that light energy into food. Light does not reach everywhere, though. Sunlight reaches only the top of the ocean, and below about 1,000 meters the ocean is completely dark. Even there, hot springs called hydrothermal vents have living things that do not depend on sunlight.

Now picture the Sun vanishing. We would not know for about 8 minutes, and then the sky would go dark. The Moon would go dark too. It does not make its own light: it shines because sunlight lights up and reflects off its surface. Distant stars, though, would still be visible. Without sunlight, light would come only from other sources: electric lights, fire, living things that glow (bioluminescence) and fluorescence. People would also lose track of day and night.

The Sun does one more job. Its gravity pulls on Earth and the other planets and keeps them circling around it, and the path each one follows is called its orbit. If the Sun vanished, Earth would keep its path for about 8 minutes. Then it would leave its orbit and move off in a straight line, along with the other planets. Nothing in this picture would make Earth stop in place: it would keep moving, only no longer in a circle around the Sun.

The Sun is a yellow dwarf star, only an average star in size: stars up to 100 times larger have been found. It is one star among 100 billion or more in our galaxy, the Milky Way, and the nearest other star, Proxima Centauri, is about 4.24 light-years away, as of November 2026. The Sun formed about 4.6 billion years ago when a giant spinning cloud of gas and dust, the solar nebula, collapsed under its own gravity. Earth has some heat of its own, too. Geothermal energy is heat energy from the earth: geo means earth and thermal means heat.

Words to know

• photosynthesis: plants making food
• orbit: path around something
• bioluminescence: living glow
• geothermal: earth heat