SDO sun

The sun erupts with extreme ultraviolet light in this 25-image mashup. (Photo: NASA/SDO)

Everyone knows not to look directly at the sun. But NASA's Solar Dynamics Observatory, which was launched into orbit in 2010, has been staring down our star almost nonstop for the past three years. And thanks to that long, unblinking ogle, we now have an unprecedented view of the sun in action without the inconvenience of scorched retinas.

The video below, released this week by NASA's Goddard Space Flight Center, compresses those three years of SDO footage into about three minutes. It's not just any three years of footage, though: As NASA points out, SDO has had "virtually unbroken coverage of the sun's rise toward solar maximum, the peak of solar activity in its regular 11-year cycle."

That cycle has sparked a barrage of solar storms lately — as well as vivid aurora displays here on Earth — and it's expected to peak sometime this year. Here's a high-speed, high-definition look at its growth, using two images per day from the past three years:

NASA adds this detail about how the video was recorded:

"SDO's Atmospheric Imaging Assembly captures a shot of the sun every 12 seconds in 10 different wavelengths. The images shown here are based on a wavelength of 171 angstroms, which is in the extreme ultraviolet range and shows solar material at around 600,000 kelvins [about 1.08 million degrees Fahrenheit]. In this wavelength it is easy to see the sun's 25-day rotation as well as how solar activity has increased over three years."
Despite this rise in activity, however, the sun's looming 11-year peak may be calm by recent historical standards. After a flurry of flares and other eruptions in late 2011, NASA has reported low sunspot numbers for this point in a solar cycle. "It's likely to be the lowest solar maximum, as measured by sunspot 'number,' in more than a century," writes Joe Gurman, a project scientist for the agency's Solar Terrestrial Relations Observatory.

That's good news for Earth's electrical grids and satellites, which can be damaged by strong solar outbursts. But the sun is often fickle, and NASA recently predicted a second "hump" of activity this year. "If you look back in history, many of the previous solar cycles don't have one hump, one maximum, but in fact have two," NASA solar physicist C. Alex Young said in a March webcast about solar storms. "That's what we think is going to happen. So we've reached one of those humps, and we think that eventually activity will pick back up and we'll see another hump — a double-humped solar maximum."

Many researchers had forecast the current solar cycle to peak in May 2013, but its relative placidity in recent months suggests the second hump will come later, and might even stretch into 2014. That doesn't mean the sun isn't active now, though: It's still near the height of a decade-long cycle, and as a reminder, it released its strongest solar flare of the year earlier this month. Another eruption in March produced dazzling displays of northern lights, possibly foreshadowing a long-anticipated spike in aurora activity.

If you noticed the sun slightly growing or shrinking during the video above, don't worry. NASA explains that's just an illusion caused by SDO's position in geosynchronous orbit:

"During the course of the video, the sun subtly increases and decreases in apparent size. This is because the distance between the SDO spacecraft and the sun varies over time. The image is, however, remarkably consistent and stable despite the fact that SDO orbits Earth at 6,876 mph and Earth orbits the sun at 67,062 mph."
That stability is key for scientists, since it lets them study the sun with enough precision to catch flares and coronal mass ejections in the act. Aside from giving us cool time-lapse videos, the goal is to better understand what causes solar explosions, NASA says, "with the hope of some day improving our ability to predict this space weather."

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