May 2022
The Backyard Astronomer
by
Adam England

Solar Cycles and Sunspots

As the morning sun rises earlier and the evening sun sets later each day through the end of June, our nights are inversely shorter and shorter. This makes for prime viewing of our closest star, the sun.

Galileo and his contemporaries focused on the sun starting around 1609, and we have been fascinated with the detail on the sun’s “surface” ever since. The dark areas they observed were recorded and compared over time, and by 1755 it was established that a roughly eleven-year cycle of activity is visible from earth as these darker spots. That first cycle, from 1755 to 1766, is documented as cycle 1,  with high and low phases referred to as solar maximum and solar minimum. At maximum, as many as 285 sunspots have been recorded (1958), and the surface has gone more than a month (2019) with no sunspots.

For most of recorded history we have been able to view the sun only from the terrestrial standpoint, and so could only document what was visibly facing earth. As we have ventured out into the solar system a great deal of time, energy, and resources have gone into furthering our understanding of the sun and how solar cycles affect our home planet and the system. What we know is still in its infancy, but NASA’s Solar Dynamics Observatory launched in 2010, allowing us to continuously observe the sun in a range of wavelengths. The Parker Solar Probe in 2021 used special shielding to get closer to the Sun than any previous human-made object, giving us insight into the inner and outer workings of our star.

SOHO, NASA Solar Dynamics Observatory, 04/20/2022

So what’s a sunspot? Visually, they are darker than the surrounding photosphere, and often appear irregular in shape, with fuzzy, elongated filaments that look like hairs emanating from dark centers. The center averages 2,700–4,200°C, with outer penumbral filaments at about 5,500°C. This difference in temperature makes a sunspot center appear dark, though if it were isolated it would be much brighter than the full moon.

We currently understand that sunspots are slightly depressed areas of the solar surface focusing strong magnetic fields. In tracking sunspots and solar cycles over the last 400 or so years, we see related patterns of their effect on our weather and on radio communication, and eleven-year cycles have been correlated with the rings of trees and layers of deep sediment. Solar cycles may even have directly or partially caused the Little Ice Age between 1250 and 1600CE.

We are currently in solar cycle 25, with the expected maximum peaking around 2025. As of this writing there are a few sunspots on the sun’s northern hemisphere, which can be safely viewed in a few different ways. Always check your equipment for punctures or tears before observing the sun, and use your solar glasses, solar telescope filters or shadow/reflection viewers in the manner instructed.

If you would like to learn more about the sky, telescopes, or socialize with other amateur astronomers, visit us at prescottastronomyclub.org or Facebook @PrescottAstronomyClub to find the next star party, Star Talk, or event.

Adam England is the owner of Manzanita Financial and moonlights as an amateur astronomer, writer, and interplanetary conquest consultant. Follow his rants and exploits on Twitter @AZSalesman or at Facebook.com/insuredbyadam.