The sun formed from a giant, spinning cloud of gas and dust called a nebula, and it is about 4.5 to 4.6 billion years old. The sun is a star at the center of our solar system, and its gravity holds the solar system together. It is a huge ball of gas, mostly hydrogen and helium. The spectroscope combined glass prisms with a telescope to analyse the spectra of light. In 1868 Janssen and Lockyer each independently discovered a new line in the sun's spectrum, and Lockyer thought it showed an undiscovered element, which he named helium after the Greek sun god Helios. Helium is often considered a special discovery as the first and only element identified outside Earth. William Ramsay later isolated helium gas from the mineral cleveite.

Cecilia Payne's 1925 thesis showed hydrogen was a million times more abundant than the other elements. The examiner Russell called this clearly impossible, and in the final thesis she wrote that the enormous abundance was almost certainly not real. Today we know that about three quarters of the sun's mass is hydrogen, almost all of the rest is helium, and 1.69 percent is other gases and metals. The sun is a yellow dwarf, a medium-size kind of star. It is about 100 times wider than Earth, and it would take 1.3 million Earths to fill it. It is not a solid ball, and you could not stand on its surface. There are billions of stars like our sun in the Milky Way galaxy.

Fusion happens only in the core of the sun, where protons of hydrogen atoms violently collide and fuse to create helium atoms, and this makes the sun's energy. The core is about 27 million degrees Fahrenheit, while the surface is about 10,000 degrees Fahrenheit. As of November 2026, the sun fuses around 620 million metric tons of hydrogen into helium every second. Neutrinos are more difficult to detect and account for only about two percent of the sun's total energy. The inside of the sun has three parts: the core, the radiative zone and the convection zone. It takes photons around 170,000 years to pass through the radiative zone, whose temperature is about seven million degrees Celsius at the base and two million at the top.

Sunlight changes on its way down to us. The sun is about 93 million miles from Earth, and its energy travels to Earth at the speed of light as electromagnetic radiation, so the light takes about 8 minutes to get here. As it passes through the atmosphere, some of it is absorbed, scattered and reflected by air molecules, water vapor, clouds, dust and pollutants. When the sun's rays are vertical, the Earth's surface gets the most energy possible. Slanted rays pass through more atmosphere, and the greatest amount of solar energy reaches Earth around solar noon. The amount of light emitted by the sun is relatively constant, varying by less than 0.01% over each decade. Besides light, the sun gives off heat, and its light and heat warm Earth and make life possible. Nothing could live on the sun, but its energy is vital for most life on Earth. Never look directly at the sun without special eye protection made for looking at the sun.

Farther out, the convection zone reaches from a depth of about 200,000 km to the visible surface, where its motion appears as granules and supergranules. Today scientists also listen to what goes on inside the sun, and that work has a name. Helioseismology, or solar seismology, is the study of the oscillations that take place within the sun. Astronomers see the sun's sound waves by measuring the Doppler shift across the sun's surface, and as the waves travel into the sun they are refracted toward the surface by changes in temperature, density and composition. Robert Leighton discovered that small areas of the sun's surface oscillated up and down with a period of about five minutes, and the sun has been likened to a bell being struck continuously.

Words to know

• spectroscope: prism and telescope
• helium: second lightest element
• oscillations: back-and-forth motions
• helioseismology: sun-oscillation study