# STEREO: NASA\'s Solar TErrestrial RElations Observatory

NASA\'s STEREO mission is a two-spacecraft mission launched with the
goal of better understanding solar activity and its effects at Earth and
throughout the solar system. STEREO is especially focused on a kind of
solar activity known as Coronal Mass Ejections (or CMEs), huge
explosions that can blow a billion tons of matter off the Sun at a
million miles an hour. Each spacecraft supports an array of imaging
telescopes and scientific radio receivers to observe solar storms from a
distance and also sensors to measure the space environment at the
spacecraft.

# STEREO and 3D 

The two spacecraft were launched together in October 2006 from Cape
Canaveral. In the following months they were placed in two separate
orbits about the Sun - one (the STEREO-A or *Ahead* spacecraft) moving
ahead of Earth\'s orbit, the other (STEREO--B or *Behind*) moving behind
Earth\'s orbit. Both spacecraft are separating from each other and
Earth.

![](media/image1.jpeg){width="5.997222222222222in"
height="4.081944444444445in"}

Animation at
<http://stereo.gsfc.nasa.gov/img/animations/movies/STEREO_heliolg2-07A.mpg>

This gives the spacecraft two points of view of the Sun and solar
storms. The two spacecraft serve as two eyes watching the Sun, allowing
us to make these "3D" images.

Most human beings use what is known as binocular vision to perceive
depth and see the world in 3D. The binocular vision system relies on the
fact that we have two eyes, which are a few centimeters apart. This
separation causes each eye to see the world from a slightly different
perspective. The brain fuses these two views together. It understands
the differences and uses them to calculate distance, creating our sense
of depth and ability to gauge distance.

Human binocular vision is limited to a few meters by the distance
between our eyes. With STEREO we want to get 3D information about what
is occurring on the Sun, which is about 150 million km (93 million
miles) away. Thus we need \"eyes\" that are much farther apart. At the
time these images were taken in late March 2007, the two STEREO
spacecraft were about 10 million km apart. This is far enough to give
each spacecraft a distinct point of view of the structures in the Sun\'s
lower atmosphere and makes 3D images of the Sun possible for the first
time.

**STEREO Ultraviolet Images**

Most of the images shown are produced by the STEREO Extreme UltraViolet
Imaging Telescopes (EUVIs). These show the Sun\'s super-hot atmosphere
in ultraviolet wavelengths of light invisible to the human eyes and
unobtainable from the Earth\'s surface. This hot, ionized material is
shaped by the Sun\'s magnetic fields so that observing the Sun\'s
atmosphere in ultraviolet light allows us to study its magnetic field.

The Sun\'s atmosphere, the corona, is shaped by the Sun\'s complex and
dynamic magnetic field. All the structures you see in these 3D movies
are the result of that field. The magnetic field is also the source of
solar activity. Complex magnetic fields rearrange and reconnect to form
simpler magnetic structures and in the process release energy in the
forms of flares and coronal mass ejections.

Each of the four wavelengths observed with the EUVI telescope
corresponds to a different temperature range in the Sun's atmosphere.
They are 304 Å: 60,000 -- 80,000 C (100,000-140,000 F); 171 Å: 1 million
C (1.8 million F); 195 Å: 1.4 million C (2.5 million F) ; 284 Å: 2.2
million C (4 million F).

# STEREO Coronagraphs and Heliospheric Imagers

In addition to the EUVI telescope, each STEREO spacecraft also carries
two coronagraphs (COR1 and COR2) and two Heliospheric Imagers (HI1 and
HI2). The coronagraphs image the Sun's corona in visible light by
placing an occulting disk in front of the bright Sun. This creates an
artificial total solar eclipse and allows us to see the much fainter
corona.

The Heliospheric Imagers are designed to observe the corona even farther
way from the Sun (where it is even fainter!). They are off-pointed to
the side rather than centered on the Sun.

The five imagers on each STEREO spacecraft allow us to image all the way
from the Sun to the orbit of the Earth. That way we can trace the motion
of a coronal mass ejection though that entire distance.

# Educational Activities 

## Matching Magnetic Fields and Active Regions

A quick activity drawing the connection between bright ultraviolet
active regions and areas of high magnetic fields

<http://stereo.gsfc.nasa.gov/classroom/matching/matching_activity.shtml>

*Mapping Magnetic Field Lines* -A teacher\'s guide.

Students map magnetic fields for themselves.

[http://cse.ssl.berkeley.edu/SegwayEd/lessons/exploring_magnetism/Exploring_Magnetism/s1.html -
act1](http://cse.ssl.berkeley.edu/SegwayEd/lessons/exploring_magnetism/Exploring_Magnetism/s1.html#act1)

Part of the *Exploring Magnetism* series.

<http://cse.ssl.berkeley.edu/SegwayEd/lessons/exploring_magnetism/Exploring_Magnetism/index.html>

## 

## Create Your Own 3D Images

How to make your own 3D images with an electronic camera

<http://stereo.gsfc.nasa.gov/classroom/3d.shtml>4/25/07