For millennia, humanity has respected the sun as an essential phenomenon in their lives; a giant ball of constantly burning hydrogen and helium, evenly spreading light across the globe.
A closer inspection of our sun reveals a surprising amount of variability. Inside, a churning mass of charged material called plasma spins magnetic fields, forms dark sunspots, and unleashes planet-shattering explosions as solar flares and coronal mass ejections (CMEs). This chaotic solar activity creates space weather and magnetic storms of superheated gas clouds that can slam into the Earth and disrupt electronics, navigation systems, and satellites.
The right side of this image taken July of 2011 displays significantly more solar activity than the left side taken March of 2017. Credit: NASA
The magnetic poles flip about every 11 years, creating sun cycles of increased and decreased activity that impact the total energy output across decades and centuries. Launched in 2010, NASA’s Solar Dynamics Observatory (SDO) has observed a full solar cycle, imaging and probing the full structure of the Sun from its deep interior to its outermost atmosphere.
SDO’s scientific focus is on examining the magnetic field generated in the interior solar dynamo and how that magnetic energy is converted and released into the heliosphere and geospace as solar wind, energetic particles, and variations in solar irradiance. As scientists continue to study SDO’s data, they refine our ability to predict and understand solar events and conditions that influence life on Earth.
The capabilitites of SDO substantially advanced the field of heliophysics taking HD quality, timelapse videos of the Sun. Collecting 1.4 terrabytes of data per day, SDO maintains a geosynchronous orbit to transmit the data directly to a NASA ground station at White Sands Missile Range in New Mexico.
Atmospheric Imaging Assembly (AIA)
Fully assembled SDO observatory. The four telescopes of the AIA protrude over the top of the satellite. The HMI is seen on the top right corner with the semi-circular plates. Credit: NASA
SDO is equipped with the Atmospheric Imaging Assembly (AIA): a battery of four high-definition telescopes capable of creating full disc images of the Sun's surface and atmosphere every 10 seconds. Each 4096 x 4096 pixel image can be taken in eight wavelengths out of ten available. Selected to study specific solar behaviours, the ten wavelength bands include nine ultraviolet and extreme ultraviolet bands, and one visible light band. From its orbit 150 million km (93 million mi) away, AIA can see details on the Sun as small as 725 km (450 mi) across—equivalent to looking at a human hair held 10 m (33 ft) away.
The solar magnetic field is generated inside the sun and emerges on the surface, which creates loops, dark cornal holes and bright spots. These images indicate how these field lines reach high above the Sun, and connect the two magnetic poles of active regions (which appear brighter in the extreme UV images and black and white in the magnetogram image) with other active regions as well. Black is where the magnetic field is pointing towards the Sun, and white is where the magnetic field is pointing away from the Sun. However, most of the Sun is covered by tiny magnetic field elements, which connect to the "quiet" features seen in the coronal image. Credit: NASA
SDO uses an instrument called the Helioseismic Magnetic Imager (HMI) to map the magnetic fields on the Sun’s surface (photosphere), and track the subsurface movement of materials. As the name indicates, HMI uses seismology to peer through the Sun’s corona, chromosphere and phosphere–140,000 miles of overlying hot gas.
Just as geologists probe Earth’s interior using waves generated by earthquakes, solar physicists can probe the Sun’s interior using acoustic waves generated by the Sun’s own boiling turbulence. Scientists learn about the temperature, chemical makeup, pressure, density, and motions of material throughout the Sun by analyzing the detailed properties of these waves. Heliophysics use this data to track the strength and direction of the solar magnetic field. When combined with measurements from AIA, scientists can further study how that magnetic field triggers CMEs and heats the corona to produce flares.
Achievements
The images collected by SDO enabled scientists to view the innerworkings of the Sun, advancing our understanding of heliophysics.
In February 2012, SDO captured images showing strange plasma tornados on the solar surface. Later observations found these tornadoes, which were created by magnetic fields spinning the plasma, could rotate at speeds up to 186,000 miles per hour. On Earth tornadoes only reach speeds of 300 miles per hour.
Global Circulation
The surface (photosphere) of the Sun is not solid; it is continually flowing due to the intense heat trying to escape and the rotation of the Sun. Large-scale circulation patterns called Meridonial circulation move through the mid-latitudes as hotter elements rise to the surface and sink down as they cool off. SDO’s observations revealed that these circulations are much more complex than scientists initially thought and are linked to sunspot production. These circulation patterns may even explain why at times, one hemisphere might have more sunspots than another.
Coronal Dimmings
The corona is the Sun’s superheated outer atmosphere and it can sometimes dim. Scientists have linked these coronal dimmings to CMEs. Using a statistical analysis of the large number of events seen with SDO, scientists were able to calculate the mass and velocity of Earth-directed CMEs. Furthermore, scientists hope to be able to study the space weather effects around other stars, which are too distant to directly measure their CMEs.
Coronal Holes
Credit: NASA.
At times, the Sun’s surface is marked by large dark patches called coronal holes where extreme ultraviolet emission is low. Coronal holes are also magnetically open areas generating high-speed solar wind streams into space. Linked to the Sun’s magnetic field, the holes follow the solar cycle, increasing at the solar maximum. When they form at the top and the bottom on the Sun they’re called polar coronal holes and SDO scientists were able to use their disappearance to determine when the Sun’s magnetic field reversed — a key indicator of when the Sun reaches solar maximum.
New Magnetic Explosions
Imaged for the first time, a forced magnetic reconnection is caused by a prominence from the Sun. The inset shows a close-up of the reconnection event imaged by SDO’s Atmospheric Imaging Assembly instrument, where the signature X-shape is visible. Credit: NASA/SDO/Abhishek Srivastava/IIT(BHU)
Using data from SDO, Scientists confirmed a decades-old theory when they discovered a whole new type of magnetic explosion: forced reconnection. They occur when a nearby explosion squeezes the plasma and magnetic fields, causing them to reconnect. These reconnection events also generate heat which may explain why the Sun’s atmosphere is significantly hotter than the photosphere: 6,000 C (11,000 F) vs 1 million C (1.8 million F). It may also lead to breakthroughs in controlled fusion and lab plasma experiments.
Deciphering Solar Explosions
