The sun emits nearly every form of electromagnetic radiation, from radio waves to gamma rays. The bulk of its energy, though, falls in three bands: about 49% is infrared (heat), 43% is visible light, and roughly 7% is ultraviolet. That remaining 1% includes everything from X-rays to radio waves. On top of electromagnetic radiation, the sun also throws off a constant stream of charged particles known as the solar wind.
Why the Sun Radiates at All
Deep in the sun’s core, hydrogen nuclei are crushed together under extreme pressure and temperature to form helium, a process called nuclear fusion. This produces gamma rays, the highest-energy photons in the universe. But those gamma rays don’t shoot straight out into space. They collide with particles inside the sun billions of times, losing energy at each interaction, gradually shifting to lower-energy forms of radiation over hundreds of thousands of years as they work their way outward.
By the time that energy reaches the sun’s visible surface, called the photosphere, it radiates outward much the way any hot object glows. A glowing iron bar shifts from red to orange to white as it gets hotter. The sun works the same way. Its photosphere averages about 5,600 Kelvin (roughly 9,600°F), which places the peak of its radiation squarely in the visible light range. This is why sunlight looks white to our eyes: it’s a broad mix of all visible colors, peaking near yellow-green.
The Three Main Bands
Almost all solar energy, about 99%, arrives in wavelengths between 300 and 3,000 nanometers. That span covers three categories.
Infrared radiation makes up the largest share at roughly 49% of total solar output. These wavelengths sit just beyond the red end of visible light, from about 700 nanometers up to 1 millimeter. You can’t see infrared, but you feel it as warmth on your skin.
Visible light accounts for about 43%, spanning wavelengths from roughly 390 to 780 nanometers. This narrow slice of the spectrum is the only part human eyes can detect, running from violet at the short end through blue, green, yellow, and orange to red at the long end.
Ultraviolet (UV) radiation contributes around 7% of the sun’s energy. It sits just below violet light in wavelength (100 to 400 nanometers) but carries more energy per photon. UV is the portion most responsible for sunburn, skin aging, and skin cancer risk, so it gets outsized attention relative to its small share of total output.
UV Subtypes and What Reaches You
Solar ultraviolet radiation breaks into three subtypes based on wavelength and biological impact.
- UVA (315–400 nm) passes through the ozone layer essentially unfiltered. It’s the weakest of the three per photon but penetrates deeper into the skin than UVB. UVA intensity stays relatively steady throughout the day and across seasons.
- UVB (280–315 nm) is mostly absorbed by the ozone layer, though enough gets through to cause sunburn and contribute to skin cancer. Its intensity peaks around midday and during summer months.
- UVC (100–280 nm) is the most energetic and most dangerous type, but it never reaches the ground. The ozone layer and upper atmosphere absorb it completely.
Nearly all UV radiation you’re actually exposed to on Earth’s surface is UVA, with a small but significant dose of UVB mixed in.
X-Rays, Gamma Rays, and Solar Flares
The sun does emit X-rays and gamma rays, but not in the steady, predictable way it emits visible light. These high-energy emissions are tied to violent events on the sun’s surface, particularly solar flares. During a flare, magnetic field lines snap and reconnect, accelerating electrons and protons to extreme speeds. Those particles produce bursts of X-rays and gamma rays that can spike dramatically over minutes or hours before fading.
None of this high-energy radiation reaches Earth’s surface. The atmosphere blocks it entirely. But it does affect the upper atmosphere, temporarily altering the ionosphere in ways that can disrupt radio communications and GPS signals.
Radio Waves From the Sun
At the opposite end of the spectrum, the sun is also a source of radio waves. During quiet periods, the photosphere emits radio waves with wavelengths around 1 centimeter, while the corona (the sun’s outer atmosphere) produces longer wavelengths approaching 1 meter. During solar flares, the sun emits short bursts of radio energy at wavelengths from about 1 to 60 meters, strong enough to be picked up by ground-based radio telescopes.
At longer radio wavelengths, the sun’s apparent size grows dramatically, because at those frequencies you’re effectively “seeing” the corona rather than just the photosphere. The corona extends millions of kilometers above the visible surface.
The Solar Wind: Particle Radiation
Beyond electromagnetic radiation, the sun constantly streams charged particles into space. This solar wind is composed mainly of protons and electrons, with about 8% alpha particles (helium nuclei) and trace amounts of heavier elements like carbon, nitrogen, oxygen, and iron. These particles travel at speeds of 300 to 800 kilometers per second.
During intense solar events, the sun also ejects bursts of higher-energy particles called solar energetic particles. These events send accelerated protons, electrons, alpha particles, and heavier ions racing through interplanetary space. Earth’s magnetic field deflects most of this particle radiation, funneling some toward the poles where it collides with atmospheric gases and creates the aurora borealis and aurora australis.
How Much Energy Reaches Earth
The total solar energy arriving at the top of Earth’s atmosphere, measured perpendicular to the sun’s rays, is about 1,361.6 watts per square meter. This value, called total solar irradiance, was refined by NASA satellite measurements and is slightly lower than the older estimate of 1,366 watts per square meter that was used for decades. Averaged over the entire globe (accounting for nighttime, the planet’s curvature, and the poles), the figure drops to about 340 watts per square meter.
Not all of that makes it to the surface. The atmosphere absorbs roughly 16% of incoming solar radiation under clear skies, primarily through ozone (which absorbs UV), water vapor (which absorbs certain infrared wavelengths), and oxygen. The remaining 84% reaches the ground, where it warms land and ocean surfaces and powers photosynthesis. Clouds, of course, reflect and absorb additional radiation on overcast days, reducing what actually arrives at the surface well below that 84% figure.