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THE SUN  

Why We Study the Sun  
The Big Questions  
Magnetism - The Key  

SOLAR STRUCTURE  

The Interior  
The Photosphere  
The Chromosphere  
The Transition Region  
The Corona  
The Solar Wind  
The Heliosphere  

SOLAR FEATURES  

Photospheric Features  
Chromospheric Features  
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Solar Wind Features  

THE SUN IN ACTION  

The Sunspot Cycle  
Solar Flares  
Post Flare Loops  
Coronal Mass Ejections  
Surface and Interior Flows
Helioseismology  

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The Key to Understanding the Sun

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Solar Magnetic Fields

Magnetism is the key to understanding the Sun. Magnetic fields are produced in the Sun by the flow of electrically charged ions and electrons. Sunspots are places where very intense magnetic lines of force break through the Sun's surface. The sunspot cycle results from the recycling of magnetic fields by the flow of material in the interior. The prominences seen floating above the surface of the Sun are supported, and threaded through, with magnetic fields. The streamers and loops seen in the corona are shaped by magnetic fields. Magnetic fields are at the root of virtually all of the features we see on and above the Sun. Without magnetic fields the Sun would be a rather boring star.

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Measuring Magnetic Fields

Magnetic forces change the direction of motion of moving charged particles like electrons. Because of this, electrons that orbit around a nucleus in one direction will have more energy than electrons that orbit about the nucleus in the opposite direction. This allows us to remotely measure the Sun's magnetic field by observing the difference in the energy of the light emitted as these electrons jump from orbit to orbit. With the proper instrumentation we can determine both the strength and the direction of the magnetic field all across the surface of the Sun.

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Modeling Magnetic Fields

Magnetic field lines loop through the solar atmosphere and interior to form a complicated web of magnetic structures. Many of these structures are visible in the chromosphere and corona, the outermost layers of the Sun's atmosphere. However, we usually measure the magnetic field itself in the photosphere, the innermost layer of the Sun's atmosphere. Techniques can be used to mathematically map these magnetic field lines into the outer layers where they can be compared with the observed structures.

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Predicting Space Weather

A better understanding of the Sun's magnetic field and its behavior will allow us to make better predictions of space weather. Observations of magnetic fields associated with solar flares show that flares are likely to occur when the magnetic field lines linking two sunspots become sheared or twisted. Observations of the Sun's magnetic field over the last 20 years illustrates its behavior over two sunspot cycles. Predicting long-range behavior, such as the size of the sunspot cycle, is currently based on simplified ideas about the magnetic cycle and previously observed behavior. We hope that in the near future we will understand the Sun well enough to make these predictions based on current conditions and past history using a mathematical model of the actual processes.

 

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NASA Logo Image Author: Dr. David H. Hathaway, david.hathaway @ nasa.gov
Curator: Mitzi Adams, mitzi.adams @ nasa.gov

Last Updated: August 11, 2014