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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
Coronal Features
Solar Wind Features

THE SUN IN ACTION �

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

THE MSFC SOLAR GROUP �

The People
Their Papers
Their Presentations

RESEARCH AREAS �

Flare Mechanisms
3D Magnetic Fields
The Solar Dynamo
Solar Cycle Prediction
Sunspot Database
Coronal Heating
Solar Wind Dynamics

PREVIOUS PROJECTS �

GOES SXI Instrument
MSFC Magnetograph
MSSTA
Orbiting Solar Obs.
Skylab
Solar Maximum Mission
SpaceLab 2
The Sun in Time (EPO)
TRACE
Ulysses
Yohkoh

CURRENT PROJECTS �

GONG
Hinode
RHESSI
STEREO
SDO
SOHO

FUTURE PROJECTS �

Solar Probe
Interstellar Probe

VIDEOS �

Solar Probe Plus

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.

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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
sdo.gsfc.nasa.gov/data/ - Latest Images from the Solar Dynamics Observatory
National Space Weather Program - The U.S. Government and Space Weather
First Gov Image + NASA Privacy Policy and Important Notices
+ Visit Solar Terrestrial Probes Program
+ Visit Living With a Star Program
NASA Logo Image Author: Dr. David H. Hathaway, david.hathaway @ nasa.gov
Curator: Mitzi Adams, mitzi.adams @ nasa.gov

Last Updated: August 11, 2014