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PAGES ARE NOT PRINTING FULL SIZE Set your printer to print 100% and make sure “print to fit” is not checked under printer setup or printer options. ASYPDF026 © 2013 Kalmbach Publishing Co. This material may not be reproduced in any form Solar science without permission from the publisher. www.Astronomy.com Opening a new window on the With three instruments operating 24/7, the Solar Dynamics Observatory is gleaning new insights into how magnetic fields control solar activity. by W. Dean Pesnell fter a year in orbit, NASA’s observatory into Earth orbit. Although Solar Dynamics Observatory the launch went smoothly, as SDO tra- (SDO) has started to fulfill its versed the surrounding atmosphere, it promise. The mission’s task: demonstrated how the observatory could to examine the Sun in such affect observations of solar phenomena. Adetail that astronomers will be able to A large winter storm over the eastern understand how our star’s magnetic field United States the previous day brought drives solar prominences, flares, coronal cold temperatures to central Florida. mass ejections (CMEs), and other solar Coupled with a thin layer of cirrus activity. And, just as important, the obser- clouds, the chill produced a sundog — a vatory will measure the changes in the rainbow-colored patch of light 22° from Sun that cause space weather, whose the Sun. A sundog arises when sunlight effects range from power outages and refracts through six-sided ice crystals all navigation problems on Earth to creating aligned with their broad sides down. drag on satellites in orbit. As SDO climbed through the cirrus Pat Corkery/United Launch Alliance Corkery/United Pat SDO began its mission February 11, cloud deck, a sound wave emanating The Solar Dynamics Observatory launches 2010. That day, an Atlas V rocket roared from the rocket caused the sundog to from Cape Canaveral February 11, 2010, atop to life on Space Launch Complex-41 at disappear. Apparently, the wave either an Atlas V rocket with a Centaur upper stage. Cape Canaveral, Florida, and lofted the evaporated the ice crystals or destroyed These colorful Suns show our star’s appearance July 28, 2010, at five A massive solar prominence (upper left) erupts from the Sun March 30, wavelengths in the extreme ultraviolet portion of the electromagnetic 2010. Scientists created this false-color, multiwavelength image with data spectrum. By observing the Sun at different high-energy wavelengths, from the Solar Dynamics Observatory. The orange-red background images solar scientists will learn how the Sun converts energy in its magnetic on this page show the Sun’s chromosphere that same day in the light of fields into the heat that drives solar flares. NASA/SDO/AIA Science Team ionized helium (a wavelength of 30.4 nanometers). NASA/SDO/AIA Science Team www.Astronomy.com 25 1:20 P.M. EDT 1:40 P.M. EDT 2:00 P.M. EDT On March 30, 2010, a large prominence erupted on the Sun’s limb and spewed hot gas into space at speeds of approximately 435 miles per second (700 km/sec). This sequence of six images from the Solar Dynamics Observatory shows the eruption lasted only a couple of hours. The observatory captured these images in the light of singly ionized helium (a wavelength of 30.4 nanometers). NASA/SDO/AIA Science Team their matching orientations. So, within maps the so-called vector magnetic field, offers more information, the line-of-sight minutes of launch, SDO already had the component directed across our line of measurements are easier to produce. impacted solar observations. But the real sight, every 15 minutes. SDO’s second instrument is the proof of the mission’s significance would The instrument makes these maps with Extreme ultraviolet Variability Experi- come only when the observatory began polarizing filters that measure how the ment (EVE). Developed at the University viewing the Sun in earnest from its perch velocity and magnetic field change. To of Colorado’s Laboratory for Atmospheric far above Earth’s atmosphere. gauge velocity, they measure the Doppler and Space Physics and the University of shift — the change in wavelength as the Southern California, EVE has three spec- SDO’s three-pronged attack distance between the Sun and SDO varies. trographs that measure the solar spectral The Solar Dynamics Observatory uses As the solar surface enlarges, and thus irradiance — the amount of energy the three instruments to study the Sun’s mag- moves toward SDO, the wavelength Sun emits at a given wavelength— for netic field. Scientists designed these tools decreases; as the solar surface shrinks, the wavelengths between 0.1nm and 105nm. to probe the Sun from below its surface wavelength increases. EVE also includes a out to the hot corona. Their goal: to find Astronomers track As soon as the small X-ray imager. how the magnetic field changes over time. these changes by observ- Extreme ultraviolet Scientists at Stanford University and ing one particular spec- detectors reached radiation from the Sun the Lockheed Martin Space Astrophysics tral line over time — in heats and ionizes the Laboratory (LMSAL) developed the Heli- this case, iron at 617.3 operating upper parts of Earth’s oseismic and Magnetic Imager (HMI). It nanometers — and temperature, the atmosphere to such a studies the behavior of the motions of the seeing how its incoming degree that scientists Sun’s surface and also the magnetic fields wavelength changes. The Sun put on a show. call it the “heartbeat of there. The Sun is a combination of gas velocity maps essentially space weather.” and its extremely hot, and thus ionized, build ultrasounds of the Sun that reveal The third instrument aboard SDO is counterpart known as plasma; its “sur- what is going on below its surface. Scien- the Atmospheric Imaging Assembly face” (or photosphere) is the region from tists use the same spectral line to chart the (AIA), which scientists at LMSAL also which light escapes into space. Every 45 behavior of magnetic fields at the surface. developed. It studies how the solar seconds, HMI makes maps of both veloc- Space-weather forecasters use the line- corona responds to the magnetic fields ities (the motions) and “line-of-sight” of-sight maps to anticipate solar flares that HMI observes near the Sun’s surface. magnetic fields at the solar surface. It also and CMEs. The vector-field maps, mean- AIA’s four telescopes focus light onto while, show the strength and direction of four CCD cameras and take images of the W. Dean Pesnell is the project scientist for the magnetic field as it emerges through Sun’s atmosphere at 10 wavelengths: one NASA’s Solar Dynamics Observatory. the surface. Although the vector field in visible light, two in the ultraviolet part Wavelength: 450nm Wavelength: 33.5nm Wavelength: 30.4nm Wavelength: 21.1nm Wavelength: 19.3nm Wavelength: 17.1nm Wavelength: 13.1nm February 1, 2011 February February 14, 2011 February The Sun’s character changes when viewed at different wavelengths. In visible light (far left), its photosphere typically reveals sunspots. But at shorter wavelengths in the extreme ultraviolet, the Sun’s outer atmosphere (its chromosphere and corona) come into view. NASA/SDO/AIA Science Team 26 Astronomy • May 2011 2:20 P.M. EDT 2:40 P.M. EDT 3:00 P.M. EDT of the spectrum, and seven in the extreme HMI even saw a sunspot before the heit (–70° Celsius), an enormous promi- ultraviolet part that corresponds to the instrument’s door fully opened. Almost nence erupted off the Sun’s limb. (See the ionization states of iron and helium. Data immediately after the EVE doors opened sequence of images above and the large from the iron spectral lines allow SDO at 2:43 p.m. EDT March 26, active region photo on page 25.) scientists to map the corona’s temperature 11057 provided fireworks. The hot spot The images show that the ring-shaped from 0.6 to 20 million kelvins; the helium fired off four relatively small flares start- prominence sent a pulse of plasma rush- observations probe temperatures from ing at 5:08 p.m. EDT. ing away from the Sun at a speed of about 30,000 to 100,000 K. But the Sun saved its best for last. 435 miles per second (700 km/s). Before Because EVE and AIA fly together, Although AIA scientists opened their the eruption, this prominence was a long solar astronomers can associate most doors March 27, they kept their CCDs tube of magnetically contained material changes in the Sun’s irradiance with spe- hot to drive off contaminants. On March just above the visible surface. Then, by cific events, such as flares, simply by align- 30, just after the CCDs reached their some still poorly understood mecha- ing changes in EVE’s measurements with operating temperatures of –94° Fahren- nisms, it destabilized and created a small changes in the AIA images.