Seeing the Invisible
Auroras are a visible sign of the magnetic mayhem in our atmosphere, but
beyond that, the human eye can’t detect much of what we call space
weather. That’s because most of the material flowing from Sun to Earth is
too small, too diffuse, or too dim—when measured against the background of
space or the brightness of the Sun—to register in the visible portion of
the spectrum.
For instance, since the corona is only visible to the naked eye during an
eclipse, scientists must use an occulting disk—which blocks out the light
from the solar surface to create an artificial eclipse—to detect what the
Sun is spitting into space. Some of the most important recent advances in
understanding and tracking coronal mass ejections have come from cameras
that photograph the corona and detect the plasma of a CME as it heads
toward Earth.
In order to see the invisible, space physicists rely on telescopes that
detect visible light, ultraviolet light, gamma rays, and X rays. They use
receivers and transmitters that detect the radio shock waves created when
a CME crashes into the solar wind (the equivalent of a sonic boom in
space). They employ particle detectors to count ions and electrons,
magnetometers to record changes in magnetic fields, and cameras to observe
the auroral patterns over the whole Earth.
All of these instruments and many others are the tools of the hundreds of
scientists participating in the International Solar-Terrestrial Physics
(ISTP) program, a global effort to observe and understand our star and its
effects on our environment. An armada of more than 25 satellites carry
those instruments into space, and together with ground-based
observatories, they allow scientists to study the Sun, the Earth, and the
space between them. Individually, the spacecraft contributing to ISTP act
as microscopes, studying the fine detail of the Sun, the solar wind, and
the boundaries and internal workings of Earth’s magnetic shell. When
linked together with each other and the resources on the ground, they act
as a wide-field telescope that sees the entire Sun-Earth environment.
The spacecraft of ISTP—principally, Wind, Polar, Geotail, and the Solar
and Heliospheric Observatory—allow physicists to observe all the key
regions of Earth’s space. They study the interior of the Sun, its surface
and corona, the solar wind, and Earth’s magnetosphere, including the
auroral regions and Van Allen radiation belts. Orbiting as far as one
million miles and as close as a few hundred miles from Earth, the
spacecraft of ISTP make coordinated, simultaneous observations of the Sun
and activity in the magnetosphere. Working together with ground
observatories, these spacecraft can now—for the first time ever—track CMEs
and other space weather events from cradle to grave. Someday, they might
even be able to predict the arrival and effects of CMEs.
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