A favorite afternoon pastime with the kids and grandkids is to check out sunspots. We have a small backyard telescope. We use it, not to look at the sun directly, but to project the sun's image onto white paper. We do this to avoid permanent eye damage -- the sure result of looking directly at the sun through a telescope.

Lately this diversion is a complete bust. No sunspots. Not one. In fact, as of last week, there have been 200 days in 2008 with no visible sunspots. What is wrong with the sun? Nothing.

What we see (or in this case, do not see) is a low point in an 11-year-long cycle of sun activity. The number of sunspots and solar flares goes from high, to low, to high in about 11 years. We are in the middle of a trough, and no sunspots are visible.

The German astronomer S.H. Schwabe discovered the 11-year cycle by counting sunspots, starting in 1826. In 1843 he was confident he saw the up-and-down pattern in his 17-year-long sun observations.

The Swiss astronomer Rudolf Wolf researched the records of other astronomers. From them he found details of sunspot watching, and he extended the solar cycle all the way back to Galileo in the 1600s.

NASA's Marshall Space Flight Center keeps track of sunspot activity and makes predictions of the coming solar cycle. Their predictions are based on measurements of the Earth's magnetic field, which is affected by the sun's activity, and by using prior cycles.

We are now in the trough of cycle 23, counting from Schwabe's first, and NASA has predictions for cycle 24 posted on the Web. The solar cycle is now calculated as 131 months +/- 14 months long -- about 11 years.

Scientists such as NASA physicist David Hathaway assure us that this current lull in the sun's activity is nothing new. There are even more disconcerting older observations.

A most unusual event occurred from 1645 to 1715. During that 70-year period, called the Maunder Minimum, there were very few sunspots, even at the 11-year peaks. Activity dropped from thousands of sunspots to handfuls.

The Maunder Minimum coincides with the coldest part of the Little Ice Age (1300s-1700s), when deep winters affected Europe and North America. For this (and other motives) scientists study the relation between solar activity and climate change -- so far, a difficult undertaking.

Solar activity also affects a key tool used by archaeologists. Carbon-14 (radiocarbon) dating is a widely used technique to date organic materials with ages up to 50,000 years.

Solar activity, the solar wind in particular, deflects the cosmic rays that form C-14 in our atmosphere. In periods of high solar activity, C-14 production is low (and vice-versa). Dates produced by C-14 dating must take the variation of solar activity into account.

Sunspots, even when absent, provide plenty for scientists to consider. The relations between the visible sunspots, the sun's magnetic activity, and weather and climate change on Earth are present but often difficult to correlate. Yet, the shortand long-term impact of our energy-filled neighbor the sun is so important to our weather and climate that careful study has a big payoff.