- A friendly, science-grounded tour of how the SUN makes light, how that light travels, and how it shapes planets, weather, technology, and life.
The SUN at a glance
The SUN is a middle-aged, G-type main-sequence star about 150 million km from Earth. It supplies nearly all the energy that drives our planet’s weather, oceans, and ecosystems.
In simple terms: the SUN is a titanic nuclear engine. It converts mass into energy in its core and radiates that energy outward as light and a steady outflow of particles.
- Type: G2V main-sequence star
- Surface (photosphere) temperature: ~5,800 K
- Core temperature: ~15 million K
- Distance to Earth: 1 Astronomical Unit (AU) ≈ 149,597,870 km
- Light travel time to Earth: ~8 minutes 20 seconds
Inside the SUN: where light is born
Deep in the SUN’s core, gravity squeezes hydrogen so tightly that atomic nuclei fuse into helium. This process—nuclear fusion—releases enormous energy as high-energy photons and neutrinos.
That energy takes a long, randomized “pinball” journey outward: first through the radiative zone, where photons scatter countless times, and then through the convective zone, where boiling currents of hot plasma ferry energy to the surface.
- Core: Fusion power plant, hydrogen → helium.
- Radiative zone: Energy diffuses via photons.
- Convective zone: Rising and sinking plasma moves heat upward.
- Photosphere: “Surface” we see; SUN-light escapes into space.
- Chromosphere & Corona: Hot outer atmosphere where solar wind begins.
What the SUN emits
The SUN’s output spans both electromagnetic radiation (light) and particles. Each part of this spectrum matters for planets, atmospheres, and technology.
- Visible light: Heats surfaces and powers photosynthesis.
- Infrared (IR): Felt as warmth; critical for climate.
- Ultraviolet (UV): Drives atmospheric chemistry, can harm biology.
- X-rays & gamma rays: Spikes during solar flares.
- Solar wind: Outflow of plasma that fills the heliosphere.
- Solar energetic particles: High-speed bursts from flares/CMEs.
- Neutrinos: Subatomic messengers from the core.
How SUN-light travels through space
Light needs no medium, so SUN-light races across the vacuum at ~300,000 km/s. Intensity decreases with distance by the inverse-square law: double the distance, quarter the light.
| World | Distance (AU) | Solar Flux (W/m²) |
|---|---|---|
| Mercury | 0.39 | ≈ 8,900 |
| Venus | 0.72 | ≈ 2,600 |
| Earth | 1.00 | ≈ 1,361 |
| Mars | 1.52 | ≈ 590 |
| Jupiter | 5.20 | ≈ 50 |
| Saturn | 9.58 | ≈ 15 |
| Uranus | 19.2 | ≈ 3.7 |
| Neptune | 30.1 | ≈ 1.5 |
How the SUN powers climate and life on Earth
On Earth, the SUN is the ultimate energy source. It warms land and oceans, fuels evaporation, stirs winds and currents, and sustains ecosystems via photosynthesis.
The SUN’s effects across other worlds
Moon
No air, direct SUN exposure causes extreme day-night temperatures.
Mercury
Closest to the SUN; experiences searing days and frigid nights.
Venus
Thick atmosphere traps SUN heat, making it hotter than Mercury.
Mars
Thin atmosphere, vulnerable to SUN storms, atmosphere erosion.
Outer Planets
Receive less SUN-light but UV still drives chemistry in atmospheres.
Solar activity & space weather
- Radio & GPS disruptions
- Satellite & astronaut radiation risk
- Power grid blackouts
- Auroras
- Atmospheric drag on satellites
A photon’s journey from the SUN
Born in the SUN’s core, a photon bounces for thousands of years before escaping the surface. Then, in 8 minutes, it crosses space to Earth, where it may warm your skin or feed a leaf.
That is the intimate connection between us and the SUN.
SUN FAQ
Is the SUN a fireball?
No. The SUN shines via nuclear fusion, not chemical burning.
Why are sunsets red?
Atmospheric scattering removes blue light, leaving reds when the SUN is low.
Will the SUN run out of fuel?
Yes, in ~5 billion years. It will become a red giant then a white dwarf.
Key takeaways about the SUN
- The SUN is a fusion engine powering the Solar System.
- Solar radiation decreases with distance (inverse-square law).
- Space weather from the SUN impacts technology and atmospheres.
- Life on Earth is possible only because of the SUN.
