Thursday, June 23, 2016


For the second time this month, the solar disk is blank--no sunspots. This image of the sun taken by NASA's Solar Dynamics Observatory on June23rd shows zero dark cores:

What does this mean? The solar cycle is like a pendulum, swinging back and forth between periods of high and low sunspot number every 11 years. Today's blank sun is a sign that the pendulum is swinging toward low sunspot numbers. In other words, Solar Minimum is coming.

Forecasters expect the next Solar Minimum to arrive 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. When the sunspot cycle reaches its nadir, a whole year could go by without sunspots.
Don't expect space weather to grow quiet, however. 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, a cosmic ray surge is already underway.

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