Structure of the Sun - Regions, Layers and Features of the SunGuide to the structure of the Sun, its different layers, regions and features and their composition and importance to space weather.
The sun is a star, just like the other stars we see at night. The difference is distance - the other stars we see are light-years away, while our sun is only about 8 light minutes away. This makes researching and investigating the regions and features of the Sun relatively easy.
Never look directly at the Sun. Even without a telescope or binoculars, the intensity of direct Sunlight is sufficient to permanently damage your eyes or cause blindness.
Structure of the Sun
The sun is composed of gas. It does not have a solid surface or continents like Earth, nor does it have a solid core. However, it still has a defined structure.
About 73% of the Sun's mass is hydrogen, and another 25% is helium. All the other chemical elements make up only 2% of our star. Most of the elements found in the Sun are in the form of atoms, with a small number of molecules, all in the form of gases: the Sun is so hot that no matter can survive as a liquid or a solid. In fact, the Sun is so hot that many of the atoms in it are ionized, that is, stripped of one or more of their electrons. This removal of electrons from their atoms means that there is a large number of free electrons and positively charged ions in the Sun, making it an electrically charged environment.
The Sun consists of many layers, not unlike an onion. The photosphere is regarded as the surface of the Sun, however, the photosphere is the layer where the Sun becomes opaque and marks the boundary past which we cannot see. The atmosphere can be thought of as being "foggy". We can see so far into the fog, but there is a point where we can see no further. The same is true for the Sun's atmosphere. It doesn't mean that the photosphere or layers above or below are significantly more or less dense. If you were falling into the Sun, you would not feel any surface but would just sense a gradual increase in the density of the gas surrounding you. It is much the same as falling through a cloud while skydiving.
The three major structural areas of the sun are shown in the graphic below, along with the three main atmospheric areas.
- Corona - The extremely hot outermost layer, extending outward several million miles from the chromosphere.
- Chromosphere - The area between the photosphere and the corona; hotter than the photosphere.
- Photosphere - The innermost part of the sun's atmosphere and the only part we can see.
- Convective zone - The outermost ring of the sun, comprising 30 per cent of its radius.
- Radiative zone - The section immediately surrounding the core, comprising 45 per cent of its radius.
- Core - The centre of the sun, comprising 25 per cent of its radius.
Surface Features of the Sun
The Sun's surface features are quite visible, but only with special equipment. For example, sunspots are only visible with special light-filtering lenses.
Different features are visible when viewing various wavelengths using filters.
You can read more about the wavelengths, frequencies and imaging of the Sun in the article linked below.
Sunspots
The most noticeable surface features of the Sun are cooler, darker areas known as sunspots. Sunspots are located where loops of the Sun's magnetic field break through the surface and disrupt the smooth transfer of heat from lower layers of the Sun, making them cooler, darker, and marked by intense magnetic activity. Sunspots usually occur in pairs. When a loop of the Sun's magnetic field breaks through the surface, a sunspot is created where the loop comes out and where it goes back in again. Sunspots usually occur in 11-year solar cycles, increasing from a minimum number to a maximum number and then gradually decreasing to a minimum number again.
Solar Flares
There are other types of interruptions of the Sun's magnetic energy. If a loop of the Sun's magnetic field snaps and breaks, it creates solar flares, which are violent explosions that release huge amounts of energy. These project solar matter and ionised ions out into space.
Solar Prominences
Another highly visible feature of the Sun is solar prominences. If plasma flows along a loop of the Sun's magnetic field from sunspot to sunspot, it forms a glowing arch that reaches thousands of kilometres into the Sun's atmosphere. Prominences can last lengths of time ranging from a day to several months. Prominences are also visible during a total solar eclipse.
How the Feature of the Sun Affect Space Weather
Space weather refers to the environmental conditions in Earth's magnetosphere, ionosphere and thermosphere due to the Sun and the solar wind. The solar wind can influence the functioning and reliability of space-borne and ground-based systems and services or endanger property or human health.
You can use the link below to read more about space weather and how the Sun affects the Earth.
Solar Glossary
| Term | Definition |
|---|---|
| Aurora | Light radiated by atoms and ions in the ionosphere excited by charged particles from the Sun, mostly seen in the magnetic polar regions. |
| Chromosphere | The part of the solar atmosphere that lies immediately above the photospheric layers. |
| Corona | The outer (hot) atmosphere of the Sun. |
| Coronal Hole | A region in the Sun's outer atmosphere that appears darker because there is less hot gas there. |
| Granulation | The rice-grain-like structure of the solar photosphere; granulation is produced by upwelling currents of gas that are slightly hotter, and therefore brighter, than the surrounding regions, which are flowing downward into the Sun. |
| Photosphere | The region of the solar (or stellar) atmosphere from which continuous radiation escapes into space. |
| Plasma | A hot ionized gas. |
| Solar Wind | A flow of hot, charged particles leaving the Sun. |
| Transition Region | The region in the Sun's atmosphere where the temperature rises very rapidly from the relatively low temperatures that characterize the chromosphere to the high temperatures of the corona. |
