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STEREO mission graphic

Solar Terrestrial Relations Observatory

Phase: Operating

Launch Date: October 25, 2006

Mission Project Home Page -

Program(s):Heliophysics Research, Solar Terrestrial Probes

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STEREO image of sun

First Ever STEREO Images of the Entire Sun
Four years after launch NASA's two STEREO spacecraft are now 180 degrees apart and able to image the entire Sun.

Check out solar activity in three dimensions ยป

STEREO (Solar TErrestrial RElations Observatory) is the third mission in NASA's Solar Terrestrial Probes program (STP). This two-year mission will provide a unique and revolutionary view of the Sun-Earth System. The two nearly identical observatories - one ahead of Earth in its orbit, the other trailing behind – will trace the flow of energy and matter from the Sun to Earth as well as reveal the 3D structure of coronal mass ejections and help us understand why they happen. STEREO will also provide alerts for Earth-directed solar ejections, from its unique side-viewing perspective adding it to the fleet of Space Weather detection satellites.

Why the need for STEREO? Coronal mass ejections (CMEs), are powerful eruptions that can blow up to 10 billion tons of the Sun's atmosphere into interplanetary space. Traveling away from the Sun at speeds of approximately one million mph (1.6 million kph), CMEs can create major disturbances in the interplanetary medium and trigger severe magnetic storms when they collide with Earth's magnetosphere.

Large geomagnetic storms directed towards Earth can damage and even destroy satellites, are extremely hazardous to Astronauts when outside of the protection of the Space Shuttle or the International Space Station performing Extra Vehicular Activities (EVAs), and they have been known to cause electrical power outages. Solar ejections are the most powerful drivers of the Sun-Earth connection. Yet despite their importance, scientists don't fully understand the origin and evolution of CMEs, nor their structure or extent in interplanetary space. STEREO's unique stereoscopic images of the structure of CMEs will enable scientists to determine their fundamental nature and origin.

STEREO - 3D image of the Sun

This was taken on April 30, 2007 with the EUVI instruments on each spacecraft at 171 Angstroms.

Image Credit: NASA


Understanding the difference between harmful and harmless coronal mass ejections is one of the biggest questions that scientists studying the face of the Sun. Currently, scientists only see ejections in one dimension. To understand how solar storms travel through the solar systems, scientists need a three-dimensional view of the storms.

STEREO, launched on Oct. 25, 2006, consists of observation systems orbiting the Sun in front of and behind the Earth. Just as our two eyes give us a three-dimensional view of the world, the views provided by each STEREO system can be combined to provide a three-dimensional view of the Sun. Though the first STEREO images were taken in early December, the two systems started to give three-dimensional images of our Sun in April 2007.

Focus Areas for STEREOBig Questions for STEREO Related Links
  • Press Release: NASA Spacecraft Show Three Dimensional Anatomy of a Solar Storm -
  • Video: Anatomy of a Coronal Mass Ejection -