The magnetism of solar flares (pictures)

On February 19 and 20, magnetic fields on the sun rearranged and realigned, and the two dark sunspots on the bottom, which are gigantic -- more than six Earth diameters across -- appeared suddenly, in less than 48 hours.
The sunspots evolved into what's called a delta region, in which the lighter penumbra region surrounding the sunspot exhibit magnetic fields that point in the opposite direction of those fields in the center dark area. It's an unstable configuration which we know can lead to solar flare radiation eruptions.
This image combines images from two instruments on NASA's Solar Dynamics Observatory: the Helioseismic and Magnetic Imager, which takes pictures in visible light that show sunspots, and the Advanced Imaging Assembly, which took an image in the 304 Angstrom wavelength showing the lower atmosphere of the sun, which is colorized in red.

This close-up view of a sunspot was captured at the Sacramento Peak Observatory of the National Solar Observatory in New Mexico.

This image from NASA's Solar Dynamics Observatory was captured on January 13 at 6:13 p.m. PT. At the center sits a large cluster of sunspots, dubbed Active Region 11654, that rotated over the left limb of the sun on January 10.
The region has been responsible for a spate of mild space weather and is now about 120,000 miles end to end, which equates about 14 Earths.

In this composite image of a coronal mass ejection captured by the Solar and Heliospheric Observatory spacecraft, an image of the sun in extreme UV light taken by the Extreme Ultraviolet Imaging Telescope (EIT) around January 4, 2002 was enlarged and superimposed on an image taken by the Large Angle and Spectrometric COronagraph (LASCO) instrument .
Direct sunlight is blocked by the sun here to reveal the surrounding faint corona.

Three images are combined here to depict a view of the sun's corona in a more narrow temperature range. AIA 211 at 3.6 million degrees Fahrenheit is red; AIA 193 at 2.5 million degrees Fahrenheit is green; and AIA 171 at the 1.8 million degree range is blue.

Active region 10486 was the largest sunspot seen by the Solar & Heliospheric Observatory (SOHO). It unleashed a spectacular show on October 28, 2003.
An X 17.2 flare, the second largest flare observed by SOHO and the third largest ever recorded, blasted off a strong high-energy proton event and a fast-moving coronal mass ejection. The spot occupied an area equal to about 15 Earths, a size not seen since 1989.
It later fired off the largest X-ray flare recorded, on November 4, 2003.

Scientists want to better understand what causes the giant explosions in the sun's corona. The eruptions, called coronal mass ejections, can send bursts of solar wind and magnetic fields toward Earth and can damage satellites and radio and electrical transmissions.

This image taken by SDO's AIA instrument at 171 Angstrom shows the current conditions of the quiet corona and upper transition region of the sun.

NASA says this sunspot, observed by the Solar Dynamics Observatory in 2011, is about 25,000 miles wide -- more than three times larger than the Earth.

Twice a year, for three weeks near the equinox, NASA's Solar Dynamics Observatory (SDO) moves into its eclipse season -- a time when Earth blocks its view of the sun for a period of time each day.
Any spacecraft observing the sun from an orbit around Earth has to contend with such eclipses, but SDO's orbit is designed to minimize them as much as possible. This image shows SDO's view of the sun being partially blocked by Earth.

In 2010 the New Solar Telescope at the New Jersey Institute of Technology's Big Bear Solar Observatory captured one of the most detailed visible light images ever of a sunspot.

One of the highlights of NASA's Solar Dynamics Observatory (SDO) during its third year in space: observations of Venus' transit across the sun. This image was taken just as Venus was leaving the disk of the sun at 12:15 a.m. ET on June 6, 2012.

On July 19, 2012, SDO captured images of a solar flare in numerous wavelengths. The 131 Angstrom wavelength, shown here in the middle and colorized in teal, portrays particularly hot material on the sun, at 10 million Kelvin, which is why the incredibly hot flare shows up best in that wavelength.
The 131 wavelength was also able to show kinked magnetic fields known as a flux rope that lay at the heart of a coronal mass ejection, which also erupted at the same time as the flare.

This double flare and a coronal mass ejection, captured in extreme ultraviolet light, erupted from the sun over a five-hour period on February 5-6.
The eruptive plasma was cooler than the surface and denser. Following the event, the magnetic field lines above the source area appeared as coils as they tried to reconnect themselves. The event also seemed to disrupt a filament to its left, highlighting its edges in white light.

NASA's Solar Dynamics Observatory captured this minor eruption on the sun on October 4, 2012.
See a movie of the eruption made using an image every 15 seconds, played back at 15 frames per second captured over a 2.5-hour time period.

Here, three images are combined to show varying temperatures. AIA 304, the chromosphere at 90,000 degrees Farenheit, is shown in red; AIA 211, the corona at 3.6 million degrees Farenheit, is green; and AIA 171, the corona at 1.8 million degrees Farenheit, is blue.

On the left we see a series of magnetic loops on the sun as captured by NASA's Solar Dynamics Observatory on July 18, 2012.
The image on the right has been processed to better define the edges of each loop, called flux rope, and further define the structures which are at the center of coronal mass ejections.
This is the first time scientists were able to discern the timing of a flux rope's formation.

AIA 211 highlights the corona, where we can see active regions, solar flare, and coronal mass ejections highlighted in brighter tones and temperatures of 3.6 million degrees Farenheit. The darker areas -- called coronal holes -- are where very little radiation is being emitted.

The AIA channel at 304 Angstroms extreme ultraviolet view shows the singly ionized helium ions, and is especially good at showing areas where cooler dense plumes of plasma are located above the surface of the sun, in the upper chromosphere and the lower transition region. The bright areas show where the plasma has a high density.

Using the Stefan-Boltzmann Law we can explain why sunspots appear dark even though they are exceedingly hot.
Sunspots have temperatures of around 4,500 K. A comparison of the power radiated per unit area of a sunspot and the surrounding surface of the sun can be made using the Stefan-Boltzmann Law.
We have (brightness of sun)/(brightness of sunspot) = (5,800 K/4,500 K)4 = 2.8 -- that is, the sun is roughly 2.8 times as bright as a sunspot.