We need the sun because it is the main source of energy, light, and stable conditions that make life on Earth possible. Without the sun, Earth would quickly become a dark, frozen planet where almost no life could survive.

What the sun does for Earth

  • The sun warms our planet enough to keep water liquid and average global temperatures around a habitable range instead of turning Earth into a frozen rock.
  • Its gravity keeps Earth in a stable orbit, giving us regular days, nights, and seasons rather than wild, lifeā€‘destroying temperature swings.
  • Sunlight powers winds, ocean currents, and the water cycle (evaporation, clouds, rain), which shape climate and support ecosystems worldwide.

How the sun supports life

  • Plants use sunlight in photosynthesis to make food and release oxygen, forming the base of almost every food chain on Earth.
  • Even fossil fuels like coal and oil are ancient ā€œstorage batteriesā€ of solar energy trapped by plants millions of years ago.
  • Without sunlight, plants would die, temperatures would plunge, and most animals and humans would eventually disappear.

The sun and our bodies

  • Sunlight helps the human body produce vitamin D, which is needed to absorb calcium and keep bones strong.
  • Light from the sun helps regulate circadian rhythms, affecting sleep and mood; regular daylight is linked with better mental wellā€‘being and activity levels.
  • Too much ultraviolet radiation can cause sunburn and increase skin cancer risk, so the same sun that helps us also requires sensible protection.

Daily life and ā€œinvisibleā€ benefits

  • Daylight makes vision possible without artificial lights and allows humans and other animals to navigate and find food more easily.
  • The sun helps define time for many cultures (days, seasons, calendars) and influences traditions and festivals that celebrate light and harvests.
  • Solar energy is also a major clean energy source, offering a longā€‘term alternative to fossil fuels for electricity and heating.

What if there were no sun?

  • Without the sunā€™s heat and light, Earthā€™s surface would cool toward deepā€‘space temperatures, making the planet far too cold for humans and most known life.
  • Photosynthesis would stop, food chains would collapse, and only a few specialized microorganisms near deepā€‘ocean vents might still endure.
  • There would be no weather, no water cycle, and no atmosphere as we know it, so Earth would become a dark, dead world instead of the living planet we experience now.

TL;DR: We need the sun because it gives Earth warmth, light, energy for food chains, stable climate, and key health benefits, all of which together make life possible and sustainable.

Information gathered from public forums or data available on the internet and portrayed here.