Let's follow the sun's energy from the very middle of the sun and work our way out. The sun is not a solid ball, and you could not stand on its surface. Fusion happens only in the core, where protons of hydrogen atoms violently collide and fuse to create helium atoms. The core is about 27 million degrees Fahrenheit. 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. The sun's energy travels to Earth at the speed of light, and the light takes about 8 minutes to get here. Its light and heat warm Earth and make life possible.

The sun gave helium its name. In 1868 Janssen and Lockyer each independently discovered a new line in the sun's spectrum. Lockyer thought it showed an undiscovered element, which he named helium after the Greek sun god Helios. Today we know that by mass, about three quarters of the sun is hydrogen, and helium makes up almost all of the rest. The sun is a huge ball of gas, mostly hydrogen and helium. It is a yellow dwarf, a medium-size kind of star, and there are billions of stars like it in the Milky Way galaxy. It is about 100 times wider than Earth, and it would take 1.3 million Earths to fill it.

People have tracked sunspots in detail since the invention of the telescope four centuries ago. Sunspots are dark, cooler spots on the sun, and a sunspot forms when intense magnetic activity in the convective zone ruptures a thermal column. Sunspots typically stretch 1,000 to 100,000 miles across, and they are areas of intense and complex magnetic fields. The number of sunspots goes up and down in a cycle of about 11 years. As of NASA and NOAA's October 2024 announcement, the sun had reached its solar maximum period, a period of the roughly 11-year cycle when the sun's magnetic poles flip. Never look directly at the sun without special eye protection made for looking at the sun.

Above the photosphere the chromosphere warms from about 6,000 to about 20,000 degrees Celsius, and across the thin transition region the plasma soars to nearly a million degrees. The corona, the outer part of the sun's atmosphere, is much hotter than the sun's surface, and scientists are still studying why the corona is hotter than the layers just below it. Parker Solar Probe launched on Aug. 12, 2018. On Dec. 24, 2024, it flew about 3.8 million miles above the sun's surface at about 430,000 miles per hour, a record for the closest approach to the sun by a spacecraft. Its 4.5-inch-thick carbon-composite shield can withstand temperatures reaching nearly 2,500 degrees Fahrenheit. As of November 2026, that remains the record.

The sun's storms reach Earth. High speed solar wind brings geomagnetic storms while slow speed wind brings calm space weather, and the effects also depend on the wind's density and magnetic field direction. A fast coronal mass ejection drives a shock wave that accelerates charged particles ahead of it and can give 15 to 60 minutes of advance warning of shock arrival at Earth. Coronal mass ejections that reach Earth can induce electrical currents in power grids and temporarily heat Earth's upper atmosphere so it swells, increasing drag on some satellites. As of NASA and NOAA's October 2024 announcement, the most powerful flare of the current solar cycle was an X9.0 on Oct. 3.

The sun will not last forever, and it is not standing still either. Every 230 million years, the sun and the solar system it carries with it make one orbit around the center of the Milky Way. It is about 4.5 to 4.6 billion years old, and as of November 2026, scientists predict it is a little less than halfway through its lifetime. A Sun-like star ends as a red giant that blows away its outer layers as a planetary nebula, leaving only its core as a white dwarf. For the sun, the red giant stage will engulf Mercury and Venus, and possibly Earth. Until then, nothing could live on the sun, but its energy is vital for most life on Earth.

Words to know

• fusion: joining atoms
• helium: second lightest element
• chromosphere: layer above photosphere
• magnetic: of magnets