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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  
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SOLAR FEATURES  

Photospheric Features  
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THE SUN IN ACTION  

The Sunspot Cycle  
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Coronal Mass Ejections  
Surface and Interior Flows
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GOES SXI Instrument
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TRACE
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SOUNDING ROCKETS  

Chromospheric Lyman-Alpha Spectro Polarimeter (CLASP)
CLASP2
CLASP2.1
Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)

CURRENT PROJECTS  

GONG
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The Sun in Time  
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Eclipses and the Sun -- Girl Scouts

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Interstellar Probe

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The Solar Wind

The solar wind streams off of the Sun in all directions at speeds of about 400 km/s (about 1 million miles per hour). The source of the solar wind is the Sun's hot corona. The temperature of the corona is so high that the Sun's gravity cannot hold on to it. Although we understand why this happens we do not understand the details about how and where the coronal gases are accelerated to these high velocities. This question is related to the question of coronal heating.

DialPlot.jpg (12900 bytes)

Click on image for larger version.

Solar Wind Variations

The solar wind is not uniform. Although it is always directed away from the Sun, it changes speed and carries with it magnetic clouds, interacting regions where high speed wind catches up with slow speed wind, and composition variations. The solar wind speed is high (800 km/s) over coronal holes and low (300 km/s) over streamers. These high and low speed streams interact with each other and alternately pass by the Earth as the Sun rotates. These wind speed variations buffet the Earth's magnetic field and can produce storms in the Earth's magnetosphere.

The Ulysses spacecraft completed two orbits through the solar system during which it passed over the Sun's south and north poles. Its measurements of the solar wind speed, magnetic field strength and direction, and composition have provided us with a new view of the solar wind. Ulysses was retired on June 30, 2009.

The Advanced Composition Explorer (ACE) satellite was launched in August of 1997 and placed into an orbit about the L1 point between the Earth and the Sun. The L1 point is one of several points in space where the gravitational attraction of the Sun and Earth are equal and opposite. This particular point is located about 1.5 million km (1 million miles) from the Earth in the direction of the Sun. ACE has a number of instruments that monitor the solar wind and the spacecraft team provides real-time information on solar wind conditions at the spacecraft.

Solar wind conditions for the last seven days

Solar wind conditions for the last 24 hours

Solar Wind Web Links

The Ulysses Mission

Advanced Composition Explorer Mission

Web Links
NOAA's Space Weather Prediction Center - Today's Space Weather Updated Every 5-minutes
NOAA's Solar Data Services - Includes Irradiance, Emissions, Sunspot Data (also Ancient), Flares, Corona, and Plage
SDO Data - Latest Images from the Solar Dynamics Observatory
National Space Weather Program - The U.S. Government and Space Weather
High-Energy Astrophysics - MSFC's Imaging X-Ray Polarimetry Explorer (IXPE)
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+ Visit Solar Terrestrial Probes Program
+ Visit Living With a Star Program
NASA Logo Image Author: Dr. David H. Hathaway, dave.hathaway @ comcast.net
Curator: Mitzi Adams, mitzi.adams @ nasa.gov
NASA Official: Dr. David McKenzie david.e.mckenzie @ nasa.gov
Last Updated: August 11, 2014