The part of the sun commonly called its surface is the photosphere. It is roughly 4,500 to 6,000 degrees Celsius, and NASA gives about 5,500. Sunspots are dark, cooler spots on the sun. They are often around 6,000 degrees Fahrenheit, while the rest of the photosphere is around 10,000. Magnetic snarls prevent heat from flowing to the surface, which creates the darker, cooler regions. These spots typically stretch 1,000 to 100,000 miles across. Their number goes up and down in a cycle of about 11 years. The peak of sunspot activity is called solar maximum, and the lull is called solar minimum. Never look directly at the sun without special eye protection made for looking at the sun.

Solar flares are classified by peak X-ray emission into classes A, B, C, M and X, and each class is ten times higher than the one before. A flare's X-rays and extreme ultraviolet can cause a radio blackout, the absence of HF communication, mainly in the 3 to 30 MHz band. Blackouts are rated on a five-level NOAA scale. Light from a solar flare travels at the speed of light and reaches Earth about 8 minutes after the flare happens. The sun also sends out a steady stream of charged particles called the solar wind, and coronal holes produce fast solar wind, 500 to 800 kilometers a second.

Coronal mass ejections travel at speeds from slower than 250 kilometers a second to nearly 3000. The fastest Earth-directed ones arrive in 15 to 18 hours, and slower ones take several days. Solar storms and fast solar wind can cause a geomagnetic storm, a disturbance in Earth's magnetic field. Auroras happen when charged particles collide with the upper atmosphere of Earth. Aurora electrons follow Earth's magnetic field down to the polar regions. The lights are best seen in an oval-shaped region between about 60 and 75 degrees north or south latitude. During large events, they can be observed as far south as the US, Europe and Asia.

People have tracked sunspots in detail since the invention of the telescope four centuries ago. Sunspot cycles are numbered, beginning with solar cycle 1 in 1755. As of November 2026, solar cycle 24 began in December 2008, peaked in April 2014 and ended in December 2019, which also marked the beginning of Solar Cycle 25. Probes now study the sun up close. As of November 2026, NASA says its Parker Solar Probe in 2021 became the first spacecraft to fly through the corona, the sun's upper atmosphere. ESA's Solar Orbiter launched in February 2020, and it is the first spacecraft to image the sun's poles from outside the ecliptic plane. Scientists are still studying why the corona is hotter than the layers just below it.

The sun formed from a giant, spinning cloud of gas and dust called a nebula. It is about 4.5 to 4.6 billion years old. Every 230 million years, the sun and the solar system it carries with it make one orbit around the center of the Milky Way. As of November 2026, scientists predict it is a little less than halfway through its lifetime. When the sun starts to die it will expand into a red giant that engulfs Mercury and Venus, and possibly Earth. National Geographic says it will reach about 200 times its current radius. For now, nothing could live on the sun, but its energy is vital for most life on Earth.

Words to know

• sunspots: cooler dark spots
• photosphere: visible surface
• aurora: polar sky lights
• corona: upper atmosphere