Journey Through the Solar System: Our Sun
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In addition to being the central source of light and heat
in our solar system, the Sun has also been a source of historical,
religious, and scientific inspiration. Because of the important role the
Sun plays in our lives, it has been studied more than any other object
in the universe, outside our own planet Earth. Today, solar physicists
delve into its structure and activities to understand more about how it
and other stars work.
Edited and updated by Carolyn Collins Petersen.
Edited and updated by Carolyn Collins Petersen.
The Sun from Earth
Observing the Sun requires special precautions because it is so bright. It's never safe to look at it through a telescope unless your telescope has a special solar filter.
One fascinating way to observe the Sun is during a total solar eclipse. This special event is when the Moon and Sun line up as seen from our point of view on Earth. The Moon blocks the Sun out for a short time and it's safe to look at it. What most people see is the pearly white solar corona stretching out into space.
Influence on the Planets
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The Sun also emits a constant stream of particles called the "solar wind" that bathes all of the planets in radiation. This wind is an invisible connection between the Sun and all the objects in the solar system, driving seasonal changes. On Earth, this solar wind also affects currents in the ocean, our day to day weather, and our long-term climate.
Mass
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Inside the Sun
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First, energy is produced in the very center, called the core. There, hydrogen fuses to form helium. The fusion process creates light and heat. The core is heated to more than 15 million degrees from the fusion and also by the incredibly high pressure from the layers above it. The Sun's own gravity balances out the pressure from heat in its core, keeping it in a spherical shape.
Above the core lie the radiative and convective zones. There, the temperatures are cooler, around to 7,000 K to 8,000 K. It takes a few hundred thousand years for photons of light to escape from the dense core and travel through these regions. Eventually, they reach the surface, called the photosphere.
The Sun's Surface and Atmosphere
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Above the chromosphere lies the corona. It's the Sun's outer atmosphere. This is the region where the solar wind exits the Sun and traverses the solar system. The corona is extremely hot, upwards of millions of degrees Kelvin. Until recently, solar physicists didn't quite understand how the corona could be so hot. It turns out that millions of tiny flares, called nanoflares, may play a role in heating up the corona.
Formation and History
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The Sun formed in a cloud of gas and dust starting about 4.5 billion years ago. It began shining as soon as its core started fusing hydrogen to create helium. It will continue this fusion process for another five billion years or so. Then, when it runs out of hydrogen, it will start fusing helium. At that point, the Sun will go through a radical change. Its outer atmosphere will expand, which will likely result in the complete destruction of planet Earth. Eventually, the dying Sun will shrink back to become a white dwarf, and what's left of its outer atmosphere may be blown to space in a somewhat ring-shaped cloud called a planetary nebula.
Exploring the Sun
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The best known-ground based solar telescopes are the Swedish 1-meter observatory on La Palma (Canary Islands), the Mt Wilson observatory in California, a pair of solar observatories on Tenerife in the Canary Islands, and others around the world.
Orbiting telescopes give them a view from outside our atmosphere. They provide constant views of the Sun and its constantly changing surface. Some of the best-known space-based solar missions include SOHO, the Solar Dynamics Observatory (SDO), and the twin STEREO spacecraft.
One spacecraft actually orbited the Sun for several years. it was called the Ulysses mission. It went into a polar orbit around the Sun on a mission that lasted
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