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 -- many thousands of times closer.
Officially, the sun is classified as a G2 type star, based on its temperature and the wavelengths or spectrum of light that it emits. There are lots of G2s out there, and Earth's sun is merely one of billions of stars that orbit the center of our galaxy, made up of the same substance and components.
The sun is composed of gas. It has no solid surface. However, it still has a defined structure. The three major structural areas of the sun:
- Core -- The center of the sun, comprising 25 percent of its radius.
- Radiative zone --The section immediately surrounding the core, comprising 45 percent of its radius.
- Convective zone -- The outermost ring of the sun, comprising the 30 percent of its radius.
- Photosphere -- The innermost part of the sun's atmosphere and the only part we can see.
- Chromosphere -- The area between the photosphere and the corona; hotter than the photosphere.
- Corona -- The extremely hot outermost layer, extending outward several million miles from the chromosphere.
It begins at the core.
The Fate of the Sun
The sun has been shining for about 4.5 billion years [source: Berkeley]. The size of the sun is a balance between the outward pressure made by the release of energy from nuclear fusion and the inward pull of gravity. Over its 4.5 billion years of life, the sun's radius has gotten about 6 percent bigger [source: Berkeley]. It has enough hydrogen fuel to "burn" for about 10 billion years, meaning it has a bit over 5 billion years left, and during this time it will continue to expand at the same rate [source: Berkeley].When the core runs out of hydrogen fuel, it will contract under the weight of gravity; however, some hydrogen fusion will occur in the upper layers. As the core contracts, it heats up and this heats the upper layers causing them to expand. As the outer layers expand, the radius of the sun will increase and it will become a red giant, an elderly star.
The radius of the red giant sun will be 100 times what it is now, lying just beyond the Earth's orbit, so the Earth will plunge into the core of the red giant sun and be vaporized [source: NASA]. At some point after this, the core will become hot enough to cause the helium to fuse into carbon.
When the helium fuel has exhausted, the core will expand and cool. The upper layers will expand and eject material.
Finally, the core will cool into a white dwarf.
Eventually, it will further cool into a nearly invisible black dwarf. This entire process will take a few billion years.
So for the next several billion years, humanity is safe -- in terms of the sun's existence, at least. Other debacles are anybody's guess.
TERMS TO KNOW:
Corona
(halo or crown) Thin gases make up the outer layer of the sun's atmosphere, which is about 1,000,000 miles high. The corona can be seen only during a solar eclipse
Photosphere
(sphere of light) this 340- mile- deep "surface" layer is the part of the Sun we see
SunSpots
as heat rises to the surface, magnetic fields get stirred up, creating dark patches that are about 2,200 degrees cooler than the surface
Convection Zone
currents of searing hot gas rise & fall here. The sun is so dense that it takes energy at least 1,000,000 years to go from the core to the surface
Radiative Zone
energy here radiates out from the core
Solar Flares
are sudden, bright outbursts of energy that occur around sunsposts as magnetic fields tear & reconnect. One solar flare can release the same energy as 40 billion atomic bombs.
- A solar flare is a magnetic storm on the Sun which appears to be a very bright spot and a gaseous surface eruption. Solar flares release huge amounts of high-energy particles and gases and are tremendously hot (from 3.6 million to 24 million °F). They are ejected thousands of miles from the surface of the Sun.
Core
the sun's nuclear core is about the size of Jupiter (but much denser)
Chromosphere
(sphere of colors) this part of the sun's atmosphere gets its name from the faint reddish light it gives off. Its average thickness is about 6,000 miles
Solar Wind
this stream of particles- IONS (electrically charged particles) that are given off by magnetic anomalies on the Sun which flow out from the Sun in all directions at up to 1,000,000 miles per hour! The solar wind is in essence the solar corona expanding into space.
- The solar wind is emitted where the Sun's magnetic field loops out into space instead of looping back into the Sun. These magnetic anomalies in the Sun's corona are called coronal holes. In X-ray photographs of the Sun, coronal holes are black areas. Coronal holes can last for months or years.
- It takes the solar wind about 4.5 days to reach Earth; it has a velocity of about 250 miles/sec (400 km/sec). Since the particles are emitted from the Sun as the Sun rotates, the solar wind blows in a pinwheel pattern through the solar system. The solar wind affects the entire Solar System, including buffeting comets' tails away from the Sun, causing auroras on Earth (and some other planets), the disruption of electronic communications on Earth, pushing spacecraft around, etc.
Solar Granules
each line, or squiggle is about 600 miles across. Granules occur because of the rising & falling of gases. Each one lasts about 8 minutes
Coronal Loops
magnetic loops with very strong magnetic fields. They often contain the dense, hot gas that emits intense X-ray radiation
Solar Prominences
giant arches of gas that erupt between sunspots.
- A solar prominence (also known as a filament) is an arc of gas that erupts from the surface of the Sun. Prominences can loop hundreds of thousands of miles into space.
- Prominences are held above the Sun's surface by strong magnetic fields and can last for many months. At some time in their existence, most prominences will erupt, spewing enormous amounts of solar material into space.
Coronal Mass Ejections
the most energetic solar eruptions CME's can grow larger than the Sun in a few hours. When directed toward Earth, they can disrupt communications & damage satellites.
- They are huge, balloon-shaped plasma bursts that come from the Sun. As these bursts of solar wind rise above the Sun's corona, they move along the Sun's magnetic field lines and increase in temperature up to tens of millions of degrees. These bursts release up to 220 billion pounds (100 billion kg) of plasma. CME's usually happen independently, but are sometimes associated with solar flares.
