Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715 (38 kb JPEG image). Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented.
This period of solar
inactivity also corresponds to a climatic period called the "Little Ice
Age" when rivers that are normally ice-free froze and snow fields remained
year-round at lower altitudes. There is evidence that the Sun has had similar
periods of inactivity in the more distant past. The connection between solar
activity and terrestrial climate is an area of on-going research.
Space Weather News for April 2, 2009
SPOTLESS SUNS: Yesterday, NASA announced that the sun has plunged into the deepest solar minimum in nearly a century. Sunspots have all but vanished and consequently the sun has become very quiet. In 2008, the sun had no spots 73% of the time, a 95-year low. In 2009, sunspots are even more scarce, with the "spotless rate" jumping to 87%. We are currently experiencing a stretch of 25 continuous days uninterrupted by sunspots--and there's no end in sight.
This is a big event, but it is not unprecedented. Similarly deep solar minima were common in the late-19th and early-20th centuries, and each time the sun recovered with a fairly robust solar maximum. That's probably what will happen in the present case, although no one can say for sure. This is the first deep solar minimum of the Space Age, and the first one we have been able to observe using modern technology. Is it like others of the past? Or does this solar minimum have its own unique characteristics that we will discover for the first time as the cycle unfolds? These questions are at the cutting edge of solar physics.
You can monitor the progress of solar minimum with a new "Spotless Days Counter" on spaceweather.com. Instead of counting sunspots, we're counting no sunspots. Daily updated totals tell you how many spotless days there have been in a row, in this year, and in the entire solar cycle. Comparisons to historical benchmarks put it all in perspective. Visit http://spaceweather.com for data.
100 HOURS OF ASTRONOMY: This week, astronomers are celebrating the 400th anniversary of Galileo's original telescopic exploration of the sky with "100 Hours of Astronomy," a cornerstone project of the International Year of Astronomy. Running from April 2 through April 5, many different public programs are planned worldwide. Is one of them near you? Visit the 100 Hours web site to find out: http://www.100hoursofastronomy.org/ Note that the celebration ends on Sun Day, April 5th, a special date devoted to observations of the sun: http://solarastronomy2009.org/100-hours-sunday/ .
To sign up for free space weather alerts, click here: http://spaceweather.com/services/
What's Wrong with the Sun? (Nothing)
July 11, 2008: Stop the presses! The sun is behaving normally.
So says NASA solar physicist David Hathaway. "There have been some reports lately that Solar Minimum is lasting longer than it should. That's not true. The ongoing lull in sunspot number is well within historic norms for the solar cycle."
This report, that there's nothing to report, is newsworthy because of a growing buzz in lay and academic circles that something is wrong with the sun. Sun Goes Longer Than Normal Without Producing Sunspots declared one recent press release. A careful look at the data, however, suggests otherwise.
But first, a status report: "The sun is now near the low point of its 11-year activity cycle," says Hathaway. "We call this 'Solar Minimum.' It is the period of quiet that separates one Solar Max from another."
Above: The solar cycle, 1995-2015. The "noisy" curve traces measured sunspot numbers; the smoothed curves are predictions. Credit: D. Hathaway/NASA/MSFC. [more]
During Solar Max, huge sunspots and intense solar flares are a daily occurrence. Auroras appear in Florida. Radiation storms knock out satellites. Radio blackouts frustrate hams. The last such episode took place in the years around 2000-2001.
During Solar Minimum, the opposite occurs. Solar flares are almost nonexistent while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now.
Although minima are a normal aspect of the solar cycle, some observers are questioning the length of the ongoing minimum, now slogging through its 3rd year.
"It does seem like it's taking a long time," allows Hathaway, "but I think we're just forgetting how long a solar minimum can last." In the early 20th century there were periods of quiet lasting almost twice as long as the current spell. (See the end notes for an example.) Most researchers weren't even born then.
Hathaway has studied international sunspot counts stretching all the way back to 1749 and he offers these statistics: "The average period of a solar cycle is 131 months with a standard deviation of 14 months. Decaying solar cycle 23 (the one we are experiencing now) has so far lasted 142 months--well within the first standard deviation and thus not at all abnormal. The last available 13-month smoothed sunspot number was 5.70. This is bigger than 12 of the last 23 solar minimum values."
In summary, "the current minimum is not abnormally low or long."
The longest minimum on record, the Maunder Minimum of 1645-1715, lasted an incredible 70 years. Sunspots were rarely observed and the solar cycle seemed to have broken down completely. The period of quiet coincided with the Little Ice Age, a series of extraordinarily bitter winters in Earth's northern hemisphere. Many researchers are convinced that low solar activity, acting in concert with increased volcanism and possible changes in ocean current patterns, played a role in that 17th century cooling.
For reasons no one understands, the sunspot cycle revived itself in the early 18th century and has carried on since with the familiar 11-year period. Because solar physicists do not understand what triggered the Maunder Minimum or exactly how it influenced Earth's climate, they are always on the look-out for signs that it might be happening again.
The quiet of 2008 is not the second coming of the Maunder Minimum, believes Hathaway. "We have already observed a few sunspots from the next solar cycle," he says. (See Solar Cycle 24 Begins.) "This suggests the solar cycle is progressing normally."
What's next? Hathaway anticipates more spotless days1, maybe even hundreds, followed by a return to Solar Max conditions in the years around 2012.
Stay tuned to Science@NASA for updates.