Almost Spotless

Image Credit: NASA/Solar Dynamics Observatory

Image Credit: NASA/Solar Dynamics Observatory

November 28, 2016 – The sun is gradually marching toward its solar minimum, and from November 14-18, hit its lowest level of solar activity since 2011. Solar activity is generally measured by sunspot count and for several days, the sun was nearly spotless.

Sunspots are islands of magnetism — sometimes as large as the planet Jupiter — on the surface of the sun. Sunspots are the sources of solar flares, coronal mass ejections, and intense UV radiation.

Sunspots come and go with an 11-year rhythm called the sunspot cycle. At the cycle’s peak, known as solar maximum, the sun is continually peppered with spots. But for every peak there is a valley, and during solar minimum, months can go by without a single sunspot.

Quiet suns are a natural part of the cycle discovered by German astronomer Heinrich Schwabe in the mid-1800s. Plotting sunspot counts, Schwabe saw that peaks of solar activity were always followed by valleys of relative calm -— a clockwork pattern that has held true for more than 200 years.

The last peak of activity was in early 2014 and currently, the sunspot numbers seem to be decreasing faster than expected, since the solar minimum level should not occur until 2021.

Predicting the peaks and valleys has proven troublesome because solar cycles are not always regular and can vary in length from 9 to 14 years. Some peaks are high, others low. The valleys are usually brief, lasting only a couple of years, but sometimes they stretch much longer.

In the 17th century, the sun plunged into a 70-year period of spotless quiet known as the Maunder Minimum that still baffles scientists.

Low solar activity has a profound effect on Earth’s atmosphere, allowing it to cool and contract. Space junk accumulates in Earth’s orbit because there is less aerodynamic drag. The calm solar wind whips up fewer magnetic storms around Earth’s poles. Cosmic rays that are normally pushed back by solar wind instead intrude on the near-Earth environment, where they pose a hazard to astronauts and satellites.