The sunspot cycle

The number of sunspots increases and decreases over time in a regular, approximately 11-year cycle, called the sunspot cycle. The exact length of the cycle can vary. It has been as short as eight years and as long as fourteen, but the number of sunspots always increases over time, and then returns to low again.

Video source: NASA Goddard / YouTube.

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NARRATOR: When we look up at the sun from Earth, it seems calm and unchanging. The truth is quite different.

In addition to these abrupt changes in activity, the sun also has a long-term, more regular pattern of change. This pattern is called the sunspot cycle, and a single cycle lasts for about 11 years, although it can be as short as 8 or as long as 14, and it can vary dramatically in intensity.

During one cycle, the number of sunspots, a good indication of solar activity, goes from low to high and back down to low. Solar minimum represents a period of time when sunspot numbers are relatively low, and solar maximum represents a period when sunspot numbers are relatively high. During this cycle, the location of the sunspots also changes. They are at middle latitudes during solar maximum, and move closer to the equator as the sun approaches solar minimum. At solar minimum, there are sometimes no sunspots to observe. At solar maximum there can be many at the same time.

The number of sunspots is important because sunspots are the visual markers of where powerful magnetic fields have emerged from the sun's interior. These magnetic fields power solar flares and coronal mass ejections, which can affect Earth and other objects in the solar system.

As the sunspots increase, so does the frequency and severity of flares and CMEs.

The sun's 11 year cycle is a symptom of a longer 22 year cycle called the solar cycle, or Hale Cycle, which affects the sun's magnetic fields. Every 11 years, the sun's poles flip. North becomes south and south becomes north. So every 22 years, the poles return to the position where they started the cycle.

The flip is due to the complex movement of magnetic fields inside the sun, that are constantly stretching, twisting and crossing as solar material bubbles up from the sun's core. But the exact pattern of movements is not yet mapped out. Because the sunspot cycle follows a similar pattern regardless of the orientation of the poles, it only takes half as long as the solar cycle.

The two cycles are different, but the 11-year sunspot cycle is often referred to as the solar cycle, which can be a little confusing. Right now the sun is approaching solar maximum, so flares and CMEs are more common than they were a few years ago. This cycle may peak in 2013, or early 2014, and should reach its minimum around 2020, although predictions about the sun are still uncertain.

The slower than expected progress of this sunspot cycle has led some to speculate that the next sunspot cycle might be very minimal, with few sunspots even at solar maximum. It is still far too early to know, but even if this is the case, it has happened before and isn't something to worry about. It just means that the sun would briefly be a little closer to the unchanging orb it looks like from the ground.

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