30 January 2014
Sometimes, people see spots, sick people get spots, and leopards never change their spots. But the sun is losing its spots. Spots are almost the “trademark” of the solar sphere, but all that might be changing. Sunspots are cooler and darker areas on the surface of the sun. The spots are thought to be caused by powerful and complex magnetic fields forming, changing and breaking up inside the sun. Surprisingly, it is just from these cool spots that solar flares suddenly flash out from the sun’s surface into space.
Unlike the leopard, the sun changes its spots, constantly. However, the number of spots has always changed in a predictable 11-year cycle. Beginning with the fewest spots at the solar minimum, the sun increases to a spotty and stormy solar maximum. Then, it returns to the less spotty minimum, again, and starts over. But something funny is going on.
In 2007, the sun sunk into one of its most spot-less minimums. When this happened, in the past, the sun was expected to make up for its “quiet time” later — with even more spots, storms and flares as it approached its maximum. So, solar observers braced for what they thought would be one of the most active “maximums” in recent history. But, in 2008, the spotlessness continued. With this much rest, everyone was sure the sun was ready to “party hardy.” Everyone braced for the maximum of all maximums with maybe the most active cycle in recorded history.
Spots should have started picking up by the end of 2008 but, instead, the number of spots dropped down – way down. Not since 1913, had there been a year with fewer sunspots. And 2009, the year when activity should have increasing toward the maximum, nothing happened. At least, nothing happened until December when a sudden burst of sunspots ignited hope of an expected rise towards the maximum. But it didn’t happen. In 2010, the “pick-up” in activity was definitely disappointing.
When the sun perked up, and spots increased, in 2011, there was a bit of hope, but 2012 was a big disappointment. Not giving up on the maximum, some said they had the answer. The solar maximum was doing a “double peak” – rising, in 2011, declining, in 2012, with 2013 as the big year for new sunspots. It didn’t happen. If anything, the “turnout” for new spots, in 2013, was dismal. What’s the big deal about 2013? Well, it should have been the solar maximum, but was weaker than most minimums.
The sun is so quiet that it’s causing real concern. Has anything like this every happened before? Well, there was the Maunder Minimum – a time during the last half of the 17th Century when sunspots just about disappeared. There’s a certain comforting reassurance in knowing that what’s happening now has happened before. But the Maunder Minimum may have come with a price. The sun’s activity can affect atmospheric weather on Earth. During the Maunder Minimum, Europe had a record cold wave. Some called, and call, it a mini-ice age. That may be too strong, but you get the idea. It got really cold.
Could another Maunder Minimum cause an extended period of much colder temperatures? Sure. But we always think of any “decrease” in the sun’s activity as causing cold and any increase as causing warmth. But things may not be that simple. The sun’s effects on the earth’s weather might have less to do with hot or cold and more to do with disruption: extreme and unpredictable weather “events.”
More troubling than the decline in the sun’s activity is the speed of the decline. A decrease in solar activity has never happened so suddenly in recorded history. By checking polar ice cores, researchers can estimate increases and decreases in solar activity going back into prehistoric times. What have they found? Solar activity hasn’t decreased this quickly in the last 10,000 years. So, we can’t look back to any period of history for the recorded effects of this kind of change. Without that, we can’t be sure what these speedy changes in the sun’s activity may bring.
Some have expressed concerns that sun may be shrinking. In the 17th century, French astronomer Jean Picard was the first to measure the sun’s diameter. Working during the period of the Maunder Minimum, he found the sun to be larger than it is today. Could that be true? Well, instruments weren’t as reliable in those days. The atmosphere, itself, affects the accuracy of the images from telescopes, so there might have been a “margin of error.
Researchers are, now, using space telescopes to try to get the best measurements possible. So far, careful observation from space seems to show that the sun is shrinking. Or is it? Again, more questions. The problem with measuring a “quiet,” “spotless” sun is that it’s probably less “puffed up” than when it’s covered with spots and storms. So, the “shrinkage” may just be a temporary effect of the lack of solar activity.
For the last 19 years, instruments have been measuring TSI — total solar irradiance. TSI is the amount of energy the sun radiates out into space. Has the sun been “shining on brightly” during this period of decreased sunspot activity? No, the sun’s TSI has dropped. What does this mean? Well, once again, no one is really sure. Our ability to get good information about the sun has never been better, but understanding what all that information means is “another matter.”
At least, the sun is taking a short nap. At most, it’s burning down. In the middle? Well, no one’s sure exactly what our spotless sun is up to these days.