The extreme-ultraviolet sun as observed on Nov. 24, 2013 -- the magnetically dominated lower corona glows bright.
Image Credit: NASA/SDO
Seeing the Sun in a New Light
April 21, 2010 will be remembered as the day we saw the sun in a new light. NASA showcased the Solar Dynamics Observatory (SDO) 'first light' imagery of the sun, photographs that are 10 times the clarity of a household high definition television. After decades of solar physics research, the advanced instrumentation aboard the SDO will answer many mysteries about our nearest star and will no doubt uncover new questions. Already, solar physicists are examining whether long-standing solar theories are holding true, and the SDO's sheer power will help scientists protect the Earth against potentially paralyzing space weather. In this multicolored image, multiple wavelengths of extreme ultraviolet light (EUV) from the SDO's AIA (Atmospheric Imaging Assembly) instrument have been overlaid, highlighting solar plasma at temperatures of 60,000 Kelvin (glowing in red) to over 1 million Kelvin (blue and green). The high definition of this instrument means very tiny magnetic structures can be resolved. The AIA is continually filming the sun, tracking energetic events like coronal mass ejections (CMEs) and flares.
Image Credit: NASA/SDO
A Prominence Erupts
As part of the NASA SDO first light release, the spacecraft was lucky to capture the eruption of a prominence, a huge arc of plasma expanding into space from the solar surface (the photosphere) high into the solar atmosphere (the corona). Typically, solar prominences measure ten times the diameter of Earth. In this series of images from a prominence eruption movie, SDO captured very fine detail in plasma structure; magnetic field lines knotting together as the prominence expanded, climbing high above the sun's limb.
Image: The blotchy solar magnetic field (left
An Internal Struggle
The SDO isn't only keeping tabs on the dynamics of the solar atmosphere, it is able to measure oscillations inside the sun, gaining a better idea about how sunspots form, flares are triggered and how energy flows through the solar body. The HMI (Helioseismic and Magnetic Imager) instrument is gathering data about this seismic activity (a method known as "helioseismology") and magnetic polarity. As the sun is a jumble of tightly wound magnetic fields, north and south magnetic poles can be found dotted all over the solar surface. Tracking magnetic polarity as the magnetic field pushes through the solar surface will ultimately help solar physicists understand what makes the sun tick, aiding space weather prediction methods.
Image Credit: NASA/SDO
As a solar flare or CME erupts, a vast amount of energy is released, rapidly heating solar plasma. By studying the lower corona in EUV wavelengths, heating mechanisms can be studied and tracked. As shown here, the solar surface is covered in loops of magnetism filled with million degree plasma, a fertile region for explosive events.
Image: The spectrum of EUV emission detected
Our Variable Star
The Extreme ultraviolet Variability Experiment (EVE) on the SDO is being used to detect ultraviolet light across many frequencies. Understanding how this radiation fluctuates will help space weather scientists see how it influences our atmosphere, heating the thermosphere of the Earth and changing our ionosphere. Changes in the ionosphere are known to impact global communications, so understanding how EUV emission varies is critical.
BIG PIC: Diving Deep into a Solar Prominence (SDO First Light)
The surface of the sun has been surprisingly calm of late -- with fewer sunspots than anytime in in the last century -- prompting scientists to wonder just what it might mean here on Earth.
Sunspots have been observed for millennia -- first by Chinese astronomers and then, for the first time with a telescope, by Galileo in 1610.
Sunspots appear in roughly 11-year cycles -- increasing to a daily flurry and then subsiding drastically, before amping up again.
But this cycle -- dubbed Cycle 24 -- has surprised scientists with its sluggishness.
The number of spots counted since it kicked off in December 2008 is well below the average observed over the last 250 years. In fact, it's less than half.
"It is the weakest cycle the sun has been in for all the space age, for 50 years," National Oceanic and Atmospheric Association physicist Doug Biesecker told AFP.
The intense electromagnetic energy from sunspots has a significant impact on the sun's ultraviolet and X-ray emissions as well as on solar storms.
Solar storms can interrupt telecommunications and electronic networks on Earth. Sunspot activity can also have an impact on the Earth's climate.
Cycle 23 hit its maximum in April 2000 with an average of 120 solar spots a day. The cycle then wound down, hitting bottom around December 2008, the point at which scientists marked the start of the current cycle.
The minimal solar activity at the end of cycle 23 led astronomers to predict a slow cycle 24. But the reality fell even below expectations.
In the first year of the cycle, during which solar activity should have risen, astronomers counted 266 days without a single sun spot.
"The forecast peak was 90 sunspots," Biesecker said, noting that even though the activity has risen over the past year, "it's very clear it is not going to be close to 90."
"The sunspots number peaked last year at 67, almost half a typical cycle," he added.
The last time a sunspot cycle was this slow was in February 1906, the peak of cycle 14, with just 64 spots a day.
The "very long minimum: three years, three times more than the previous three cycles of the space age" was a major surprise, said University of Montana physicist Andres Munoz-Jamillio.
The sun's photospahere as observed by NASA's Solar Dynamics Observatory on Nov. 24, 2013. The dark spots are known as sunspots, of which there are surprisingly few at this point in the solar cycle.NASA/SDO
A Magnetic Switch
Cycle 24 has also diverged from the norm in another surprising way.
Typically, around the end of each 11-year sunspot cycle, the sun's magnetic fields switch direction. The northern and southern hemispheres change polarity, usually simultaneously.
During the swap, the strength of the magnetic fields drops to near zero and reappears when the polarity is reversed, scientists explain.
But this time, something different seems to be happening. The north pole already reversed its polarity several months ago -- and so it's now the same polarity as the south pole.
According to the most recent satellite measurements, "the south hemisphere should flip on the near future," said Todd Hoeksema, director of the Wilcox Solar Observatory at Stanford University.
He didn't seem concerned about the phenomenon.
But scientists are watching the sun carefully to see whether cycle 24 is going to be an aberration -- or if this solar calmness is going to stretch through the next cycle as well.
"We won't know that for another good three or four years," said Biesecker.
Some researchers speculate this could be the start of a prolonged period of weak solar activity.
The last time that happened, during the so-called "Maunder Minimum" between 1650 and 1715, almost no sunspots were observed. During the same period, temperatures dropped sharply on Earth, sparking what is called the "Little Ice Age" in Europe and North America.
As the sunspot numbers continue to stay low, it's possible the Earth's climate is being affected again.
But thanks to global warming, we're unlikely to see another ice age. "Things have not started to cooling, they just have not risen as quickly," Biesecker said.