Posted on by Nancy Atkinson

SDO Provides Constant, Unprecedented Views of Sun’s Inner Corona

Cosmic Radiation
This photograph of the Sun, taken by the Atmospheric Imaging Assembly (AIA) instrument on NASA's Solar Dynamics Observatory reveals the faint, inner corona. At the Sun's limb, prominences larger than the Earth arc into space. Bright active regions like the one on the Sun's face at lower center are often the source of huge eruptions known as coronal mass ejections. Credit: NASA/LMSAL/SAO

[/caption]

Usually the only time we can see the innermost part of the Sun’s corona is when there is a total eclipse. But now, with the Atmospheric Imaging Assembly (AIA) instrument on NASA’s Solar Dynamics Observatory and a new image processing program, scientists are getting unprecedented views of the innermost corona 24 hours a day, 7 days a week.

“The AIA solar images, with better-than-HD quality views, show magnetic structures and dynamics that we’ve never seen before on the Sun,” said astronomer Steven Cranmer from the Harvard-Smithsonian Center for Astrophysics (CfA). “This is a whole new area of study that’s just beginning.”

The Sun’s outer layer, or corona is composed of light, gaseous matter, and has two parts. The outer corona is white, with streamers extending out millions of miles from the edge of the sun. The inner corona, lying next to the red chromosphere, is a band of pale yellow.

This zoomed-in image shows how the Sun's magnetic field shapes hot coronal plasma. Photos like this highlight the ever-changing connections between gas captured by the Sun's magnetic field and gas escaping into interplanetary space. Credit: NASA/LMSAL/SAO

This outer layer of the Sun’s atmosphere is, paradoxically, hotter than the Sun’s surface, but so tenuous that its light is overwhelmed by the much brighter solar disk. The corona becomes visible only when the Sun is blocked, which happens for just a few minutes during an eclipse.

Now, with AIA, “we can follow the corona all the way down to the Sun’s surface,” said Leon Golub of the CfA.

Previously, solar astronomers could observe the corona by physically blocking the solar disk with a coronagraph, much like holding your hand in front of your face while driving into the setting Sun. However, a coronagraph also blocks the area immediately surrounding the Sun, leaving only the outer corona visible.

The AIA instrument on SDO allows astronomers to study the corona all the way down to the Sun’s surface.
Cranmer and CfA colleague Alec Engell developed a computer program for processing the AIA images above the Sun’s edge. These processed images imitate the blocking-out of the Sun that occurs during a total solar eclipse, revealing the highly dynamic nature of the inner corona. They will be used to study the initial eruption phase of coronal mass ejections (CMEs) as they leave the Sun and to test theories of solar wind acceleration based on magnetic reconnection.

The resulting images highlight the ever-changing connections between gas captured by the Sun’s magnetic field and gas escaping into interplanetary space.

This time-lapse movie shows two days of solar activity observed by the AIA instrument. Both the solar surface and dynamic inner corona are clearly visible in X-rays. Hot solar plasma streams outward in vast loops larger than Earth before plunging back onto the Sun’s surface. Some of the loops expand and stretch bigger and bigger until they break, belching plasma outward.

SDO launched in February 2010.

This video provides more information about the AIA instrument:

Posted on by Ian O'Neill

SoHO Celebrates its 12th Birthday

171cycle_dates.thumbnail.jpg

On December 2nd, 1995 a large joint ESA and NASA mission was launched to gain an insight to the dynamics of the Sun and its relationship with the space between the planets. 12 years on, the Solar and Heliospheric Observatory (SoHO) continues to witness some of the largest explosions ever seen in the solar system, observes beautiful magnetic coronal arcs reach out into space and tracks comets as they fall to a fiery death. In the line of duty, SoHO even suffered a near-fatal shutdown (in 1998). As far as astronomy goes, this is a tough assignment.

By the end of 1996, SoHO had arrived at the First Lagrange Point between the Earth and the Sun (a gravitationally stable position balanced by the masses of the Sun and Earth, about 1.5 million km away) and orbits this silent outpost to this day. It began to transmit data at “solar minimum”, a period of time at the beginning of the Solar Cycle, where sunspots are few and solar activity is low, and continues toward the upcoming solar minimum after the exciting firworks of the last “solar maximum”. This gives physicists another chance to observe the majority of a Solar Cycle with a single observatory (the previous long-lasting mission was the Japanese Yohkoh satellite from 1991-2001).

On board this ambitious observatory, 11 instruments constantly gaze at the Sun, observing everything from solar oscillations (“Sun Quakes�), coronal loops, flares, CMEs and the solar wind; just about everything the Sun does. SoHO has become an indispensable mission for helping us to understand how the Sun influences the environment around our planet and how this generates the potentially dangerous “Space Weather�.

The SoHO mission site confidently states that SoHO will remain in operation far into the next Solar Cycle. I hope this is the case as the new Hinode and STEREO probes will be good company for this historic mission.

Source: NASA News Release