Our Local Star: The Sun

The Sun is a medium-sized star and our nearest star. It contains most of the mass in the Solar System, so its gravity controls the orbits of the planets. The Sun is mostly hydrogen with some helium.

How the Sun Produces Energy

The Sun shines because of nuclear fusion in its core. Tiny hydrogen nuclei are squeezed together to make helium. This joining releases large amounts of energy as light and heat. Think of it like snapping two small building blocks into one larger block and getting energy out when they lock together. In a stable star like the Sun, energy made in the core balances the inward pull of gravity.

What the Sun Emits

The Sun gives out energy across the electromagnetic spectrum, mostly in the infrared, visible, and ultraviolet regions. Visible light lets us see; infrared warms the Earth; too much ultraviolet can harm skin and eyes.

Layers of the Sun (simple model)

• Core: fusion happens here; it is extremely hot and dense.
• Radiative zone: energy moves out mainly as radiation.
• Convective zone: hot gas rises and cooler gas sinks, like a boiling pan.
• Photosphere: the “surface” we see; about 5,500°C.
• Outer atmosphere (chromosphere and corona): thin and very hot; seen during total eclipses.

The Sun’s Gravity

Because the Sun holds most of the Solar System’s mass, its gravity keeps planets in orbit. The gravitational field becomes weaker with distance, so planets farther away orbit more slowly.

Light from the Sun

Light does not arrive instantly; it has a speed. The Sun is about 1 astronomical unit (AU) from Earth, and sunlight takes about 8 minutes to reach us.

The Sun in the Galaxy

The Sun is one of many billions of stars in the Milky Way galaxy. It is our local star, but not unique in the universe.

Common Misconceptions

• The Sun is not “on fire” like wood burning; it is powered by nuclear fusion.
• The Sun is a star, not a planet or a solid ball.
• Orbits are slightly elliptical; the Sun sits near a focus, not the exact center.
• Never look directly at the Sun; its light can damage eyes.