Our Neighborhood Star
The Sun is the star at the center of our solar system. It is a nearly perfect ball of hot, glowing gas called plasma. Its immense gravity holds the planets, asteroids, and comets in orbit. The Sun is the source of almost all the energy on Earth, providing the heat and light that make life possible.
The Sun's Atmosphere
While the Sun doesn't have a solid surface, it has several distinct layers. The outer layers, which we can observe, are called its atmosphere.
Photosphere: This is the lowest layer of the atmosphere and the part we see as the visible 'surface' of the Sun. Most of the light that reaches Earth comes from the photosphere. It has a granulated, bubbly appearance.
Chromosphere: This is a reddish layer of gas just above the photosphere. It is normally only visible during a total solar eclipse, when the bright photosphere is blocked by the Moon.
Corona: The corona (Latin for 'crown') is the Sun's outermost atmosphere. It is a vast, wispy layer of super-hot gas that extends millions of miles into space. Like the chromosphere, it is only visible during a total solar eclipse. The corona is mysteriously much hotter than the photosphere below it.
The Sun's Energy Source: Nuclear Fusion
How does the Sun produce so much energy? The answer lies in its core. The Sun's core is under incredible pressure and is heated to about 15 million degrees Celsius. Under these extreme conditions, a process called nuclear fusion takes place.
Nuclear Fusion is the process where the nuclei of smaller atoms are forced together to form the nucleus of a larger atom.
In the Sun's core, hydrogen atoms are fused together to form helium atoms.
During this process, a tiny amount of mass is converted into a huge amount of energy, as described by Einstein's famous equation, E = mc².
This energy slowly makes its way from the core to the photosphere, where it is released as heat and light. The Sun has been fusing hydrogen for about 4.6 billion years and has enough fuel to continue for another 5 billion years.
Solar Activity
The Sun is a very active place. Its surface is constantly changing due to its powerful and complex magnetic fields.
Sunspots: These are dark, cooler areas on the Sun's photosphere. They are caused by intense magnetic fields poking through the surface, which slows down the flow of heat from the interior. The number of sunspots increases and decreases in an approximately 11-year cycle.
Solar Flares: These are sudden, intense explosions of energy and radiation from the Sun's surface, often occurring near sunspots.
Prominences: Huge, looping arcs of gas that extend out from the Sun's surface, held in place by magnetic fields.