How do we know?
↻ One of the pages with a moving picture
We sent a spacecraft to fly through the Sun’s outer air.
- The Sun is a star: a hot, glowing ball of hydrogen and helium gas.
- In its core, bits of hydrogen smash together so hard they stick and become helium. This is nuclear fusion.
- Fusion gives off a huge amount of energy, which slowly works its way out to the surface.
- The energy pours into space as light and heat. Sunlight reaches Earth in about 8 minutes.
On 24 December 2024, NASA’s Parker Solar Probe flew just 3.8 million miles above the Sun’s surface, through the Sun’s outer air. NASA called it the closest pass to the Sun.
From Earth, big telescopes watch the Sun every day. The Inouye Solar Telescope on Haleakalā in Hawaiʻi is the largest solar telescope in the world.
The energy made in the core takes a long, slow trip to the surface. Then it crosses space as sunlight, and it reaches Earth in about 8 minutes.
Wow number
27 million °F is how hot the Sun’s core is. The surface is a “cool” 10,000 °F.
Myth or fact?
The Sun is a giant fire. Myth. Fire needs oxygen. The Sun glows because of fusion, not burning.
About 1.3 million Earths could fit inside the Sun. Fact. That is how many it would take to fill it up.
Think about it
The Sun is a star. Why do you think the other stars look so tiny and dim?
Where in the world?
Haleakalā, Maui, Hawaiʻi where the Inouye Solar Telescope watches the Sun. Parker Solar Probe blasted off from Cape Canaveral, Florida, on 12 August 2018 — 20.7067° N, 156.2575° W.
Where these facts come from
Every number on page 8, and who measured it
This page tells us the Sun is a ball of hydrogen and helium, and how hot its middle and its surface are.
Sun: Facts — NASA, the U.S. space agency
science.nasa.gov/sun/facts
We checked it on 31 October 2026
This page explains that the Sun shines by fusion, not by burning like a fire.
How can the Sun "burn"? — NASA StarChild, a NASA science site for kids
starchild.gsfc.nasa.gov/docs/StarChild/questions/question36.html
We checked it on 31 October 2026
This page tells us sunlight takes about 8 minutes to reach Earth.
Facts About Earth — NASA, the U.S. space agency
science.nasa.gov/earth/facts
We checked it on 31 October 2026
This page tells us about the giant Sun telescope on Haleakalā in Hawai'i.
Daniel K. Inouye Solar Telescope - NSO — The U.S. National Solar Observatory
nso.edu/telescopes/dki-solar-telescope
We checked it on 31 October 2026
This page tells us where and when the Parker Solar Probe blasted off.
Parker Solar Probe — NASA, the U.S. space agency
science.nasa.gov/mission/parker-solar-probe
We checked it on 31 October 2026
This page tells us how close Parker flew to the Sun on Dec. 24, 2024.
NASA’s Parker Solar Probe Makes History With Closest Pass to Sun — NASA, the U.S. space agency
science.nasa.gov/science-research/heliophysics/nasas-parker-solar-probe-makes-history-with-closest-pass-to-sun
We checked it on 31 October 2026
Has this changed?
The Sun has shone this way for a very long time, so this answer is not going to change.
What keeps changing is how closely we can look. Parker Solar Probe keeps flying through the Sun’s outer air, and every pass brings new measurements.
Words from this page
- star
- A huge ball of hot gas that makes its own light.
- core
- The very middle of the Sun, where fusion happens.
- nuclear fusion
- When tiny bits of matter smash together so hard they stick and give off energy.
Try it!
Race two ice cubes, one in the Sun and one in the shade.
1. On a sunny day, put one ice cube on a plate in the sunshine. 2. Put another ice cube on a plate in the shade. 3. Check every 5 minutes. Never look straight at the Sun!
What happens: the sunny cube melts first. Sunlight carries the Sun’s energy all the way to you.
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