Star
The Sun
The Sun is easy to treat as the bright background to everything else. It is also the object that holds most of the Solar System's mass, supplies the energy that reaches Earth, and keeps sending particles and magnetic disturbances through the space around us. Getting to know it changes how the rest of the system fits together.
Updated · About 6 minutes to read
- Type
- G-type main-sequence star
- Age
- About 4.5 billion years
- Diameter
- About 1.39 million km
- Average distance from Earth
- About 149.6 million km
- Light travel time to Earth
- About 8 minutes 20 seconds
- Visible surface temperature
- About 5,500°C
- Core temperature
- About 15 million°C
- Rotation
- Varies with latitude; not one rigid day
Rounded reference figures: NASA reference data. Distances are orbital averages, not a live position; temperatures describe the stated layer or context.
A star does not have solid ground
The Sun is largely hydrogen and helium in a hot, electrically conducting state called plasma. The visible layer is the photosphere, not a solid crust that a spacecraft could land on. Above it are the chromosphere and corona. When an image shows loops, bright patches, or a sharply defined-looking edge, it is showing light from material and magnetic structures rather than a rocky surface. The Sun also rotates at different rates at different latitudes. Near the equator, a rotation takes roughly 25 Earth days; closer to the poles it takes longer.
The energy starts with fusion
In the core, nuclear reactions convert hydrogen into helium and release energy. This is different from a fire burning fuel in oxygen. The energy eventually reaches space as sunlight after passing through the Sun's interior. Gravity pulls inward, while pressure supports the star against collapse. That balance does not make the Sun static: gas moves, magnetic fields change, and the visible layers show constant activity. Thinking about both the long-lived balance and the shorter-term motion is more useful than imagining one enormous flame.
Why the corona is such an interesting problem
The corona can be much hotter than the visible photosphere beneath it. That sounds backwards if you picture an ordinary object cooling as you move away from a heat source. The Sun's magnetic fields and plasma make the situation more complicated. Researchers study how waves and magnetic reconnection transfer energy, and how that energy is distributed through the atmosphere. A report about one heating mechanism should not be read as proof that every part of the coronal-heating problem has been solved. Different regions and conditions can involve different processes.
The solar wind connects the planets
The solar wind is a flow of charged particles moving outward from the Sun. It carries magnetic structure into interplanetary space and interacts with the environments around planets. It is not the same thing as sunlight, and a solar flare is not simply another name for the wind. The flow varies in speed and structure. Understanding where it originates and how it accelerates requires both images of the Sun and measurements made inside the moving plasma. The region dominated by this outward solar influence is called the heliosphere.
Sunspots and the activity cycle
Sunspot numbers rise and fall over a cycle of roughly 11 years. The cycle is linked to changes in the Sun's magnetic field, and its timing and strength are not identical every time. Sunspots look dark beside their surroundings because they are cooler than the nearby photosphere, not because they give off no light. Higher activity tends to bring more opportunities for flares and other eruptions. A cycle forecast describes broad behavior; it cannot tell you that a particular eruption will happen at an exact time on an exact date.
Flares, ejections, and effects near Earth
A flare is a rapid release of electromagnetic energy. A coronal mass ejection sends a large structure of plasma and magnetic field outward. They can occur together, but they are different phenomena. When solar disturbances interact with Earth's magnetic environment, the effects can include auroras and problems for communications or spacecraft. The geometry matters: an event on the Sun is not automatically headed toward Earth. Different kinds of signals also arrive on different timescales. Visible light and other electromagnetic radiation travel at light speed, while the bulk plasma takes much longer.
How spacecraft study something this extreme
Parker Solar Probe entered the corona in 2021, allowing measurements inside the Sun's outer atmosphere rather than only from far away. Its instruments examine particles and fields while its heat shield protects sensitive hardware. ESA's Solar Orbiter combines imaging with measurements of its surroundings, helping connect what happens at the Sun with material moving outward. Those are complementary approaches. An image tells us where a feature appears; an in-situ measurement tells us what the spacecraft actually encountered. Combining them is a major part of learning how the solar atmosphere works.
The poles offer another perspective
Most familiar solar images come from viewpoints close to the plane in which Earth orbits. Solar Orbiter's changing orbit provides views toward the poles, which matter for understanding the magnetic cycle. A different viewing angle is not just a nicer picture. It can reveal features that are difficult to separate when they are compressed against the edge of the visible disk. The same caution applies to colored solar imagery: different instruments observe different wavelengths, and assigned colors are a way to make those measurements visible.
Read a solar image carefully
Ask which instrument made the image, what wavelength it recorded, whether the colors are assigned, and what time the observation represents. Two images taken on the same day can look dramatically different because they reveal different temperatures or layers. The Sun in the atlas is a visual aid, not a live space-weather forecast. For an actual observing session, use specialist solar-safety guidance and proper equipment; an ordinary pair of sunglasses is not protection for looking at the Sun.
For the wider context, read How stars form, shine, and die.
A magnetic star with several observable layers
The Sun's photosphere is the visible layer from which most ordinary sunlight escapes. Above it lie the chromosphere and corona, which are studied using different wavelengths and observing techniques. A texture that looks like the Sun in one band is not a complete map of all these layers at once.
Convection transports energy toward the surface, while rotation and electrically conducting plasma contribute to magnetic activity. Sunspots, flares, prominences, and coronal mass ejections are related to that magnetic environment, but they are distinct phenomena. A flare is a burst of radiation; a coronal mass ejection expels magnetized material. Their effects at Earth depend on geometry, timing, and interaction with the near-Earth environment.
Stellar Studio exaggerates some motion and color so these ideas remain visible in a browser. Choosing a white photosphere or an eclipse treatment changes the artistic rendering, not the Sun's measured properties. Real solar monitoring relies on calibrated instruments, wavelength information, and time-stamped data. The preview is useful for comparing visual treatments while the scientific explanation belongs in the measurements and sources.