Solar Highlights of 2016/2017

Solar material twists above the sun’s surface in this close-up captured by NASA’s Solar Dynamics Observatory on June 7-8, 2016, showcasing the turbulence caused by combative magnetic forces on the sun.

This spinning cloud of solar material is part of a dark filament angling down from the upper left of the frame. Filaments are long, unstable clouds of solar material suspended above the sun’s surface by magnetic forces. SDO captured this video in wavelengths of extreme ultraviolet light, which is typically invisible to our eyes, but is colorized here in red for easy viewing.

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On July 6, 2016, engineers instructed NASA’s Solar Dynamics Observatory, or SDO, to roll 360 degrees on one axis. SDO dutifully performed the seven-hour maneuver, while producing some dizzying data: For this period of time, SDO images – taken every 12 seconds – appeared to show the sun spinning, as if stuck on a pinwheel. This video was taken by SDO’s Atmospheric Imaging Assembly instrument in extreme ultraviolet wavelengths that are typically invisible to our eyes, but was colorized here in gold for easy viewing.

This maneuver happens twice a year to help SDO’s Helioseismic and Magnetic Imager, or HMI, instrument take precise measurements of the solar limb, the outer edge of the sun as seen by SDO. Were the sun perfectly spherical, this would be a much simpler task. But the solar surface is dynamic, leading to occasional distortions. This makes it hard for HMI to find the sun’s edge when it’s perfectly still. HMI’s biannual roll lets each part of the camera look at the entire perimeter of the sun, helping it map the sun’s shape much more precisely.

HMI tracks variations in the solar limb over time to help us understand how the shape of the sun changes with respect to the solar cycle, the sun’s 11-year pattern of solar activity. The more we know about what drives this activity – activity that can include giant eruptions of solar material and radiation that can create hazards for satellites and astronauts – the better we may someday predict its onset.

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Solar material repeatedly bursts from the sun in this close-up captured on July 9-10, 2016, by NASA’s Solar Dynamics Observatory, or SDO. The sun is composed of plasma, a gas in which the negative electrons move freely around the positive ions, forming a powerful mix of charged particles. Each burst of plasma licks out from the surface only to withdraw back into the active region – a dance commanded by complex magnetic forces above the sun. SDO captured this video in wavelengths of extreme ultraviolet light, which are typically invisible to our eyes. The imagery is colorized here in red for easy viewing.

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ESA and NASA’s Solar and Heliospheric Observatory, or SOHO, saw a bright comet plunge toward the sun on Aug. 3-4, 2016, at nearly 1.3 million miles per hour. Comets are chunks of ice and dust that orbit the sun, usually on highly elliptical orbits that carry them far beyond the orbit of Pluto at their farthest points. This comet, first spotted by SOHO on Aug. 1, is part of the Kreutz family of comets, a group of comets with related orbits that broke off of a huge comet several centuries ago.

This comet didn’t fall into the sun, but rather whipped around it – or at least, it would have if it had survived its journey. Like most sungrazing comets, this comet was torn apart and vaporized by the intense forces near the sun.

The disk of the sun is represented by the white circle in this image.

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On July 24, 2016, NASA’s Interface Region Imaging Spectrograph, or IRIS, captured a mid-level solar flare: a sudden flash of bright light on the solar limb – the horizon of the sun – as seen at the beginning of this video. Solar flares are powerful explosions of radiation. During flares, a large amount of magnetic energy is released, heating the sun’s atmosphere and releasing energized particles out into space. Observing flares such as this helps the IRIS mission study how solar material and energy move throughout the sun’s lower atmosphere, so we can better understand what drives the constant changes we can see on our sun.

As the video continues, solar material cascades down to the solar surface in great loops, a flare-driven event called post-flare loops or coronal rain. This material is plasma, a gas in which positively and negatively charged particles have separated, forming a superhot mix that follows paths guided by complex magnetic forces in the sun's atmosphere. As the plasma falls down, it rapidly cools – from millions down to a few tens of thousands of Kelvins. The corona is much hotter than the sun’s surface; the details of how this happens is a mystery that scientists continue to puzzle out. Bright pixels that appear at the end of the video aren’t caused by the solar flare, but occur when high-energy particles bombard IRIS’s charge-coupled device camera – an instrument used to detect photons.

Credit: NASA/IRIS/Lockheed Martin Solar and Astrophysics Laboratory

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Early in the morning of Sept. 1, 2016, NASA’s Solar Dynamics Observatory, or SDO, caught both the Earth and moon crossing in front of the sun. SDO keeps a constant eye on the sun, but during SDO’s semiannual eclipse seasons, Earth briefly blocks SDO’s line of sight each day – a consequence of SDO’s geosynchronous orbit. On Sept. 1, Earth completely eclipsed the sun from SDO’s perspective just as the moon began its journey across the face of the sun. The end of the Earth eclipse happened just in time for SDO to catch the final stages of the lunar transit.

In the SDO data, you can tell Earth and the moon’s shadows apart by their edges: Earth’s is fuzzy, while the moon’s is sharp and distinct. This is because Earth’s atmosphere absorbs some of the sun’s light, creating an ill-defined edge. On the other hand, the moon has no atmosphere, producing a crisp horizon.

This particular geometry of Earth, the moon and the sun also resulted in a simultaneous ring of fire, or annular, eclipse visible from southern Africa. Annular eclipses are similar to total solar eclipses, except that they happen when the moon is at a point in its orbit farther from Earth than average – meaning that the moon’s apparent size is smaller, and it can’t block the entire face of the sun. This leaves a narrow ring of the solar surface visible, often called a ring of fire.

Music credit: Inner Strength by Brava [SGAE], Dsilence [SGAE], Input [SGAE], Output [SGAE] from the KillerTracks Catalog.

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In the same way that two eyes give humans a three-dimensional perception of the world around us, the twin spacecraft of NASA’s Solar Terrestrial Relations Observatory mission, or STEREO, enable us to understand the sun in 3-D. Thanks to this mission, which launched on Oct. 25, 2006, we can see and study the sun from multiple viewpoints – crucial for understanding solar activity and the evolution of space weather.

One of STEREO’s key instruments is called a coronagraph, which is used to study the corona, the sun’s outer atmosphere. Each of STEREO’s coronagraphs has a metal disk called an occulting disk. The occulting disk blocks the sun’s bright light and makes it possible to discern the detailed features of the surrounding corona, which is about one million times dimmer than the sun. Much like the way the bright headlights of a semi-truck at night hide just how big the truck is, the brightly shining sun makes it difficult to study the much fainter corona.

In celebration of the mission’s 10th anniversary, here is a guide to reading a STEREO image. Watch the video below, created with imagery of a massive July 2012 coronal mass ejection, to learn the key features of STEREO coronagraph data:

Space, in color

Each STEREO spacecraft has two coronagraphs with occulting disks of different sizes. The colors you see in the image are not true to life; scientists color the images to quickly tell which instrument in particular the image is from. In this video, the coronagraph image is colored blue.

Occulting disk

The black circle in the center of the coronagraph image is the occulting disk, which blocks the disk of the sun. The occulting disk mimics a total solar eclipse seen from Earth, in which the moon perfectly blocks the sun and allows observations of the massive corona.

The sun, in extreme ultraviolet light

Sometimes STEREO coronagraph images incorporate imagery from another one of STEREO’s instruments called the Extreme UltraViolet Imager, which captures the sun in a type of light that is invisible to human eyes. Later, these images are colorized. These extreme ultraviolet light images are sometimes imposed over the occulting disk to help give a sense of the sun’s size and position, and to provide more information as to which direction a solar eruption is headed. Extreme ultraviolet light images highlight active regions on the sun – regions where intense magnetic activity can give rise to solar eruptions. Here, STEREO observed the CME bursting forth from this active region.

Stars

Stars are often present in STEREO coronagraph images. These are the steady, brightly shining specks in the background.

Diffraction patterns

Faint ripples around the edge of the occulting disk result from diffracted light. When light enters the telescope, it hits the edge of the metal disk and bends, or diffracts, around the disk.

Streamers

Radial structures flowing out from the corona are called streamers. Solar material in streamers and the corona flow out into space to form the solar wind that fills our solar system.

Coronal mass ejections

Coronal mass ejections are eruptions of solar material that shoot far out into space, often accelerating particles ahead of them to near-light speeds. On July 23, 2012, STEREO-A saw this CME – one of the fastest on record. Scientists call this sort of CME a halo CME because the solar material forms a complete ring around the sun.

High-energy particle snow

As the CME expands beyond STEREO’s field of view, a flurry of what looks like snow floods the image. These are high-energy particles flung out ahead of the CME at near-light speeds, striking the charge-coupled device in STEREO’s camera. The immediacy and intensity of this “snowstorm” in space following the CME reflects just how fast and strong the eruption is: Less than an hour after the start of this eruption, accelerated particles traversed approximately 93 million miles from the sun to STEREO.

Music credit: Passing Images by Andrew Britton [PRS], David Goldsmith [PRS] from the KillerTracks Catalog.

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On Oct. 30, 2016, NASA’s Solar Dynamics Observatory, or SDO, experienced a partial solar eclipse in space when it caught the moon passing in front of the sun. The lunar transit lasted one hour, between 3:56 and 4:56 p.m. EDT, with the moon covering about 59 percent of the sun at the peak of its journey across the face of the sun. The moon’s shadow obstructs SDO’s otherwise constant view of the sun, and the shadow’s edge is sharp and distinct, since the moon has no atmosphere which would distort sunlight.

From SDO’s point of view, the sun appears to be shaking slightly – but not because the solar observatory was spooked by this near-Halloween sight. Instead, the shaking results from slight adjustments in SDO’s guidance system, which normally relies upon viewing the entire sun to center the images between exposures. SDO captured these images in extreme ultraviolet light, a type of light invisible to human eyes. The imagery here is colorized in red.

On Oct. 19, 2016, operators instructed NASA’s Solar Dynamics Observatory, or SDO, to look up and down and then side to side over the course of six hours, as if tracing a great plus sign in space. During this time, SDO produced some unusual data. Taken every 12 seconds, SDO images show the sun dodging in and out of the frame. SDO captured these images in extreme ultraviolet light, a type of light that is invisible to our eyes. Here, they are colorized in red

SDO operators schedule this maneuver, one of a series of maneuvers that SDO completed on Oct. 27, 2016, twice a year to calibrate the spacecraft’s instruments. Veering motions allow scientists to assess how light travels through SDO’s instruments – whether light is reflected inside the instrument, for example – and how these instruments are changing over time.

This particular maneuver is the EVE Cruciform maneuver, designed to help SDO’s Extreme ultraviolet Variability Experiment, or EVE, take accurate measurements of the sun’s extreme UV emissions. EVE studies these emissions over time, so that we may better understand their role in influencing Earth’s climate and local space environment.

Our constantly-changing sun sometimes erupts with bursts of light, solar material, or ultra-fast energized particles — collectively, these events contribute to space weather. In a study published Jan. 30, 2017, in Space Weather, scientists from NASA and the National Center for Atmospheric Research, or NCAR, in Boulder, Colorado, have shown that the warning signs of one type of space weather event can be detected tens of minutes earlier than with current forecasting techniques – critical extra time that could help protect astronauts in space.

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An active region on the sun — an area of intense and complex magnetic fields — has rotated into view on the sun and seems to be growing rather quickly in this video captured by NASA’s Solar Dynamics Observatory between July 5-11, 2017. Such sunspots are a common occurrence on the sun, but are less frequent as we head toward solar minimum, which is the period of low solar activity during its regular approximately 11-year cycle. This sunspot is the first to appear after the sun was spotless for two days, and it is the only sunspot group at this moment. Like freckles on the face of the sun, they appear to be small features, but size is relative: The dark core of this sunspot is actually larger than Earth.

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Music credit: ‘The Answer’ by Laurent Levesque [SACEM] from Killer Tracks

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