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THREE WEEKS WITHOUT SUNSPOTS: As July 17th comes to a close, the sun has been blank for 21 straight days--a remarkable 3 weeks without sunspots. To find an equal stretch of spotless suns in the historical record, you have to go back to July-August 2009 when the sun was emerging from a century-class solar minimum. We are now entering a new solar minimum, possibly as deep as the last one.
Solar minimum is a normal part of the solar cycle. Every 11 years or so, sunspot production sputters. Dark cores that produce solar flares and CMEs vanish from the solar disk, leaving the sun blank for long stretches of time. These quiet spells have been coming with regularity since the sunspot cycle was discovered in 1859.
However, not all solar minima are alike. The last one in 2008-2009 surprised observers with its depth and side-effects. Sunspot counts dropped to a 100-year low; the sun dimmed by 0.1%; Earth's upper atmosphere collapsed, allowing space junk to accumulate; and the pressure of the solar wind flagged while cosmic rays (normally repelled by solar wind) surged to Space Age highs. These events upended the orthodox picture of solar minimum as "uneventful."
Space weather forecasters have long wondered, will the next solar minimum (2018-2020) be as deep as the previous one (2008-2009)? Twenty-one days without sunspots is not enough to answer that question. During the solar minimum of 2008-2009, the longest unbroken interval of spotlessness was ~52 days, adding to a total of 813 intermittent spotless days observed throughout the multi-year minimum. The corresponding totals now are only 21 days and 244 days, respectively. If this solar minimum is like the last one, we still have a long way to go.
How does this affect us on Earth? Contrary to popular belief, auroras do not vanish during solar minimum. Instead, they retreat to polar regions and may change color. Arctic sky watchers can still count on good displays this autumn and winter as streams of solar wind buffet Earth's magnetic field. The biggest change brought by solar minimum may be cosmic rays. High energy particles from deep space penetrate the inner solar system with greater ease during periods of low solar activity. NASA spacecraft and space weather balloons are already detecting an increase in radiation. Cosmic rays alter the flow of electricity through Earth's atmosphere, trigger lightning, potentially alter cloud cover, and dose commercial air travelers with extra "rads on a plane."
At the moment there are no nascent sunspots on the solar disk, so the spotless days counter is likely to keep ticking. Stay tuned for more blank suns and … welcome to solar minimum.
FLY ME TO THE MOONSTONE: Are you looking for a far-out gift? Nothing says "I love you" like a moonstone from the edge of space. On June 12th, the students of Earth to Sky Calculus flew this moonstone wrapped in a sterling silver Celtic love knot 34.1 km (111,877 feet) above Earth's surface:
You can have it for $119.95. The students are selling these pendants to support their cosmic ray ballooning program. Each one comes with a greeting card showing the item in flight and telling the story of its journey to the edge of space. Sales support the Earth to Sky Calculus cosmic ray ballooning program and hands-on STEM research.
Far Out Gifts: Earth to Sky Store
All sales support hands-on STEM education
RED SPRITES OVER THE USA: Around Earth's northern hemisphere, thunderstorm season is in full swing. That means it's a great time to see sprites. Paul Smith photographed these specimens on July 14th:
"I was at Kaw Lake in Oklahoma when the sprites started leaping up from the thunderheads," says Smith.
Sprites are an exotic form of upward-directed lightning, reaching from the tops of electrical storms all the way up to the edge of space. Because they emerge from the tops of storms, the best place to see sprites is from a distance where the camera can point over the edge of the thunderhead.
"I was about 140 miles from the storm in Kansas that produced these sprites," says Smith. This weather map shows the location of his camera (blue pushpin) and where it was pointing (blue arrow):
People have been seeing sprites since at least the 19th century, but the first reports were met with skepticism. Sprites entered the mainstream in 1989 when researchers from the University of Minnesota finally captured them on film. Subsequent video footage from the space shuttle cemented their status as an authentic physical phenomenon.
In recent years, citizen scientists like Smith have been photographing sprites in record numbers. One reason is raised awareness. More photographers know about sprites, so more sprites are being photographed. Another reason might be a genuine increase in sprite activity. Some researchers think that sprites are linked to cosmic rays. Subatomic particles from deep space strike the top of Earth's atmosphere, producing secondary electrons that trigger the upward bolts. Cosmic rays are now intensifying due to the decline of the solar cycle. More sprites, anyone?