The Sun is constantly roiling with nuclear heat and intense
magnetism that make sunspots, flares, coronal
mass ejections, and
all sorts of space
weather. When
directed toward Earth, those solar blasts can disrupt satellite and radio
communications, damage our electric-powered tools and toys, and create auroras.
But it is not always easy to know when the Sun is spitting
plasma and energy in our direction. This is why NASA launched the Solar
Terrestrial Relations Observatory, or STEREO, in October 2006. The twin
satellites were sent out along roughly the same orbit around the Sun as the
Earth itself. The orbit of STEREO-A (ahead) is slightly closer to the Sun and
moving faster than Earth; the STEREO-B (behind) orbit is slightly farther from
the Sun and moving a little slower than our planet. The difference in speed
creates separation between the satellites and a stereoscopic view of our nearest
star.
The images above show the surface of the Sun from two different
angles on October 14, 2012. The top image is from STEREO-B and shows a dark
vertical stripe on the upper middle face of the Sun. The lower image comes from
STEREO-A, which was more than 90 degrees ahead of STEREO-B; that is, somewhat
beyond a right angle from that vertical stripe. In the lower image, the
vertical stripe instead shows up as a large loop stretching into the solar
atmosphere, or corona.
The stripe and the loop are differing views of the same dense
mass of electrified gas (plasma) held in place by a magnetic field. When viewed
straight on, as in the STEREO-B image, the line of plasma appears darker
because it is relatively cooler than the solar surface below. (More of its energy
is magnetic than radiant.) Solar scientists call these dark lines “filaments.” When viewed from the side, however,
the line of plasma looks like a bright loop stretched out against the blackness
of space; solar physicists call this a prominence.
Essentially, filaments and prominences are the same phenomenon, just viewed
from a different perspective.
As of September 1, 2012, STEREO-A and STEREO-B formed an equal-sided
triangle together
with NASA’s Solar Dynamics Observatory (SDO), which views the Sun from orbit
around Earth. This geometry allowed the three craft to provide overlapping views
of the entire Sun. It
also allows solar physicists to study solar events in three dimensions.
1. Further Reading
NASA image courtesy of the STEREO science team. Caption by Mike
Carlowicz, based on information from Karen Fox
هیچ نظری موجود نیست:
ارسال یک نظر