We’ve experienced four solar cycles of ever lower solar activity, that is, thermal irradiation and sunspots. The Sun’s output has been steadily decreasing ever so slightly over 44 years. This might sound scary…are we headed for a “mini-ice age”?
What is a solar cycle and what is the Sun is doing during the cycle?
The Sun is a small and dynamic star. It goes through cycles of activity with minima (low points) and maxima (high points). A solar cycle is the length of time between minima of solar activity. The solar cycle has been found to be 11 years from minimum to minimum. So, you have minimum, then for 5.5 years activity increases until maximum, then for 5.5 years activity decreases until minimum again. That’s one cycle.
Solar cycles were first described by Danish astronomer C. Horrebow in the mid-1700s, then German astronomer S.H. Schwabe in 1843 published his own observations. These became the basis for documenting solar cycles. Swiss astronomer Rudolf Wolf compiled these data, and Solar cycle 1 (1755-1766) was published.
Due to its variable viscosity the Sun has zones of differential rotation rates, like bubbles within bubbles that are spinning at different speeds. These differences in rotation rate cause the Sun’s magnetic field to get fragmented, shooting magnetic field lines outward, taking with them millions of tons of solar plasma. This causes solar prominences, called sunspots when viewed from above. Scientists at organizations such as NASA and NOAA study these phenomena because their frequency and numbers help determine the extent of solar activity. An early indicator of a cycle change is the polarity of sunspots. Sunspots exhibit a reverse in polarity as the cycle starts changing away from minimum or maximum.
Even before the publication of solar cycle 1, astronomers had been observing and recording sunspots. Later, in the 19th century astronomers Annie and Edward Maunder found a coincidental climate occurrence with those older sunspot records, previously compiled and published by their contemporary, Gustav Sporer. They found the years 1645-1715 were a time of unusually cold weather in Europe and of a significant drop in sunspot numbers. It is now known as the Maunder Minimum. Summers were cold, with crop failures, and winters were brutal.
The Sun has nearly completed year one of solar cycle 25, with four preceding cycles of ever decreasing activity. What does this mean? If we were living in 1700 it might mean a cooler Earth until the Sun got back in gear. Today it means a very slight moderation of global warming, but unfortunately the warming force appears stronger than the cooling force. It looks like solar cycle 25 is reversing the downward activity trend so increasing activity is expected. We’ll see what happens.
What’s in the Sky?
December 12; before sunrise/before sunset; southeast/southwest: A thin crescent Moon and Venus get close
December 13; 9pm onward; east to southeast to south: The Geminid meteor shower peaks