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Why We Study the Sun


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


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


Photospheric Features 
Chromospheric Features 
Coronal Features 
Solar Wind Features 


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


Flare Mechanisms 
3D Magnetic Fields 
The Solar Dynamo 
Sunspot Cycle Predictions 
Solar Wind Dynamics 


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The Climate Connection

The Sun is a source of light and heat for life on Earth. Our ancestors realized that their lives depended upon the Sun and they held the Sun in reverent awe. We still recognize the importance of the Sun and find the Sun to be awe inspiring. In addition we seek to understand how it works, why it changes, and how these changes influence us here on planet Earth. The Sun was much dimmer in its youth and yet the Earth was not frozen. The quantity and quality of light from the Sun varies on time scales from milli-seconds to billions of years. Some of these variations most certainly affect our climate but in uncertain ways.


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Space Weather

The Sun is the source of the solar wind; a flow of gases from the Sun that streams past the Earth at speeds of more than 500 km per second (a million miles per hour). Disturbances in the solar wind shake the Earth's magnetic field and pump energy into the radiation belts. Regions on the surface of the Sun often flare and give off ultraviolet light and x-rays that heat up the Earth's upper atmosphere. This "Space Weather" can change the orbits of satellites and shorten mission lifetimes. The excess radiation can physically damage satellites and pose a threat to astronauts. Shaking the Earth's magnetic field can also cause current surges in power lines that destroy equipment and knock out power over large areas. As we become more dependent upon satellites in space we will increasingly feel the effects of space weather and need to predict it.


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The Sun as a Star

The Sun also serves an important role in helping us to understand the rest of the astronomical universe. It is the only star close enough to us to reveal details about its surface. Without the Sun we would not have easily guessed that other stars also have spots and hot outer atmospheres. The Sun is the key to understanding other stars. We know the Sun's age, radius, mass, and luminosity (brightness) and we have also learned detailed information about its interior and atmosphere. This information is crucial for our understanding of other stars and how they evolve. Many physical processes that occur elsewhere in the universe can be examined in detail on the Sun. In this way solar astronomy teaches us much about stars, planetary systems, galaxies, and the universe itself.


The Sun as a Physical Laboratory

The Sun produces its energy by nuclear fusion - four hydrogen nuclei are fused to form single helium nuclei deep within the Sun's core. We have worked for decades to reproduce this process (in a controlled manner) here on Earth. Most of these efforts involve extremely hot plasmas  in strong magnetic fields. (This plasma is not the blood product but rather a mixture of ions and electrons produced at high temperatures.) Much of solar astronomy involves observing and understanding plasmas under similar conditions. There continues to be much interaction between solar astronomers and scientific researchers in this and many other areas.


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Author: David H. Hathaway,, (256) 961-7610
Mail Code SD50, NASA/Marshall Space Flight Center, Huntsville, AL 35812


Responsible Official: John M. Davis,, (256) 961-7600
Mail Code SD50, NASA/Marshall Space Flight Center, Huntsville, AL 35812


Last revised 2000 November 21 - D. H. Hathaway

Reproduced from