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Stargazing

By David Huestis, Historian, Skyscrapers, Inc.

Solar Variability: Our Inconstant Sun

I went to bed last night wondering where the Sun had gone. Then it dawned on me. A little astronomy humor to begin a serious discussion on our life-giving star—the Sun.

Our Sun coalesced out of a vast cloud of gas and dust some 100 times the size of our solar system roughly five billion years ago. Gravity contracted this mass until the core of this proto-star reached about 24.5 million degrees Fahrenheit. At that time nuclear fusion began, converting about 600 million tons of hydrogen to helium per second. This process has been ongoing since then.

Although our Sun is a very stable G2 yellow dwarf star, it does have a slight “variability.” Over an average 11-year cycle solar activity waxes and wanes. Most apparent of this activity manifests itself in the appearance of dark sunspots, regions of intense magnetism residing as depressions in the Sun’s photosphere (the visible “surface” of the Sun).

There is also a 22-year cycle. At the end of an 11-year cycle, groups of the new cycle have reversed polarity magnetic fields. The appearance of reversed polarity groups, along with the fact that they form at higher north and south solar latitudes, indicates the Sun is transitioning to a new cycle. However, groups of old and new polarities do coincide during the transition.

It is an easy task to follow the progress of each solar cycle. Decades ago, I used my own telescope equipped with a special solar filter to conduct sunspot counts. This process was fine for clear or partly cloudy days, but often around here in southern New England we can experience days upon days of overcast skies. Today, solar observatories orbiting the Earth provide uninterrupted high-resolution solar images, thereby making sunspot counting very convenient.

When solar activity is high, our atmosphere expands, thereby increasing drag on our orbiting spacecraft. In fact, Skylab, a United States orbital laboratory, reentered the Earth’s atmosphere ahead of schedule in July 1979 due to this specific problem. Most of it plummeted into the Indian Ocean, while some pieces fell in Western Australia.) And on March 11, 1989, Hydro-Quebec was shutdown by a huge geomagnetic storm caused by an intense solar storm. Circuit breakers tripped when transformers melted due to the amount of energy that entered the system from the event.

According to solar physicist Lisa Upton, “We expect Solar Cycle 25 will be very similar to Cycle 24: another fairly weak maximum, preceded by a long, deep minimum.” The current solar minimum will continue thru 2019, likely ending in 2020. The next solar maximum is expected in 2024-2026.

Unfortunately, the relatively small variability in solar activity has far reaching consequences for climate change. I have read reports hoping for a Maunder-type minimum in the hopes a decades-long solar minimum would mitigate the effects of global warming. Yes, global warming. Precisely stated. Climate change says little.

In 1789 Benjamin Franklin stated, “Our new Constitution is now established, and has an appearance that promises permanency; but in this world nothing can be said to be certain, except death and taxes.” While the permanency of the Sun is guaranteed for another five billion years, let’s hope extreme solar variability does not threaten our already fragile ecology.