When people ask how the Farmers’ Almanac comes up with its famous long-range forecast, we always give the same answer: “The Farmers’ Almanac bases its long-range weather forecasts on a top-secret mathematical and astronomical formula that figures in sunspot activity, tidal action, the position of the planet in relation to the Sun, and a number of other factors.”
While the rotation of the Earth around the Sun and the actions of the tides are pretty well understood, all this talk of “sunspot activity” can sound a bit like something from a science fiction novel. So, what are sunspots, anyway, and how do they influence the weather?
Sunspots were first discovered in 1612 by Italian astronomer Galileo Galilei. Shortly after creating his early version of the telescope, Galileo spotted what looked to be dark smudges visible on the sun. Ever since that time, scientists have tried to discover what causes the spots, and what they mean for us, here on Earth.
Though the Sun looks like a solid object from our vantage point on Earth, the truth is, it is a constantly changing ball of moving gasses. Sunspots are temporary regions of lower temperature that form on the Sun when magnetic activity prevents those gasses from evenly covering all areas of its surface. Though the spots are still very hot — up to 7,500º F — they appear dark in comparison to the surrounding 10,000º areas. As the gasses move, the spots not only shift in size and location, but corresponding areas of brightness occur in the form of solar flares and other events.
Ever since sunspots were first discovered, people speculated that their appearance followed some kind of regular cycle. In 1848, a man by the name of Rudolf Wolf devised the basic formula for calculating sunspots. He determined that the spots form in cycles of about 11.1 years. Wolf’s sunspot calculations continue to be used to this day, because no other index of the Sun’s cycles is as accurate or as detailed.
Though the Sun’s energy output varies by only about 0.1% over the course of a solar cycle, scientists who studied historical weather trends have found that weather patterns on Earth follow a similar 11-year cycle. Just last year, a team of researchers from the National Center for Atmospheric Research confirmed what we, at the Farmers’ Almanac, have always known: that tiny percentage difference in the Sun’s warmth causes changes in the Earth’s stratosphere drastic enough to shift global climate.