Solar scientists ask: "Where are the Sunspots?"

A popular American folk song from the early 1960s begins with the lyrics, "Where have all the flowers gone, long time passing, Where have all the flowers gone, long time ago...?" etc., etc. Well, solar scientists are singing a similar tune these days; only the words might go something like this: "Where have all the sunspots gone, long time ago...?"

The sun has no spots these days, and that simply should not be the case. Sunspots are the result of intense magnetic storms that rage on the surface of the sun. Because they tend to inhibit the natural convection that brings hotter material from inside the sun to the surface, they appear dark against the brighter solar disk.

On average, the temperature of a sunspot is about 7,640 degrees Fahrenheit, while the surface of the sun is about 9,980 degrees Fahrenheit. Associated with sunspots are solar flares, giant explosions in the sun's atmosphere that emit vast amounts of electromagnetic radiation and streams of charged particles.

When intercepted by the earth's magnetic field, these charged particles are responsible for causing the Northern and Southern Lights over the polar regions, and can even cause electrical power outages and communication interruptions.

The number of spots on the sun varies considerably over time, and they seem to come and go in 11-year cycles. This means that the length of time between two solar maximums or two solar minimums is, on average, 11 years.

The most recent solar maximum happened in 2001, when about 125 spots were recorded. This means that the solar minimum should have occurred in about 2006, and by now we should be halfway to the next maximum in 2012. But we're not. For some unknown reason, the current minimum has been extended. Last year it was expected that the sun would become more active after a quiet spell. But instead it produced a 100-year low in sunspot numbers.

According to solar physicist Dr. Louise Harra of University College London, it is unclear why this is happening or when the sun is likely to become more active again.

"There's no sign of us coming out of it yet," she said.

The sun has gone through extended periods of inactivity before. The best known of these quiet periods is called the Maunder Minimum (named for 19th Century solar astronomer Edward Maunder). From about 1645 to 1715, very few spots were seen on the sun.

Although these observations were not as extensive as in later years, the sun was examined often during this time, and the lack of sunspots is well documented.

The sun doesn't shine quite as brightly during these tranquil phases. Interestingly, this 70 years of solar calm 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.

So, if the sun doesn't start generating spots pretty soon, will our climate start to cool? According to solar researcher Professor Mike Lockwood of Southampton University, the answer is probably no. Lockwood has shown that the sun's activity has been gradually decreasing since 1985, yet overall global temperatures have continued to rise.

"If the sun's dimming were to have a cooling effect, we'd have seen it by now," says Lockwood.

But what if the sun's quiescence continues for many more years? Could we eventually see a cooling effect? Scientists simply don't know. Professor Richard Harrison of the Rutherford Appleton Laboratory in England believes this lull in activity provides a unique opportunity for solar study. He adds, "This is very exciting because, as astronomers, we've never seen anything like this before in our lifetimes."