Oct 2 2016

It’s happening again: The sunspot number has dropped to zero. Yesterday, sunspot group AR2597 vanished, leaving the face of the sun blank. There are no significant dark cores in today’s image of the sun from NASA’s Solar Dynamics Observatory:

What does this mean? Blank suns herald the coming of Solar Minimum.

The sunspot cycle is like a pendulum, swinging back and forth with a period of 11 or 12 years. Right now the pendulum is swinging toward low sunspot numbers. Forecasters expect the the cycle to hit rock bottom in 2019-2020. Between now and then, there will be lots of spotless suns. At first, the blank stretches will be measured in days; later in weeks and months. The current blank spell is the 4th such interval of 2016, so far.

Because solar flares subside during Solar Minimum, many people think space weather goes away during this time. Not so. Solar Minimum brings many interesting changes. For instance, as the extreme ultraviolet output of the sun decreases, the upper atmosphere of Earth cools and collapses. This allows space junk to accumulate around our planet. Also, the heliosphere shrinks, bringing interstellar space closer to Earth. Galactic cosmic rays penetrate the inner solar system with relative ease. Indeed, there is already evidence of increasing radiation in Earth’s atmosphere–a matter of keen interest to air travelers and possible space tourists.

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