WEBVTT FILE

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There’s a rhythm emanating from the Sun

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to the edges of the solar system.

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Roughly every 11 years, our star ramps up to a turbulent state expelling violent eruptions.

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After a peak, it calms down to a quieter phase,

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before starting all over again.

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This is known as the solar cycle.

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This ebb and flow of solar activity affects the entire solar system

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including spacecraft electronics and astronauts

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that can be affected by particle radiation if they’re not sufficiently protected.

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Understanding the solar cycle is one of the oldest problems in solar physics

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and now, predicting it is more critical than ever as we venture to the Moon and Mars, and beyond.

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So, here are ways we’ve learned about tracking it.

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[Text: 1: Count sunspots]

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So, welcome to the dome.

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Today, we’re going to observe the Sun

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and see if it has some sunspots.

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Every morning when the skies are clear,

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Olivier looks through this telescope in search of sunspots.

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These are dark blotches on the Sun that are the main source of solar eruptions.

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They appear and disappear on the Sun’s surface.

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So, we’re not looking at the Sun.

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In fact, we’re looking at the shadow of the instrument.

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Then we put the paper always at the same place

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and then we can start drawing.

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Olivier and a team of sun observers record the pattern of sunspots by pencil.

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The first known record of sunspots date back to around a thousand years ago in China.

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After the invention of the telescope in the 17th century, routine observations were made.

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Today, sunspot drawers still use the same technique.

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While we’ve created satellites that can see the Sun in much more detail in recent decades,

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drawing by hand keeps the centuries-long record consistent.

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The sunspot number record goes back farther than any other instrument

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allowing scientists to analyze the Sun’s behavior over many, many solar cycles. 

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Sunspot numbers are collected from observatories around the world and are averaged.

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During every 11-year cycle, the number of sunspots rise from zero to a peak

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and then go back down to zero again.

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Scientists use these numbers to determine when a new solar cycle begins and how active a cycle is.

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Solar maximum, the period of highest activity, can vary wildly from cycle to cycle.

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The more sunspots there are, the higher the frequency of solar storms of all types —

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some that create aurora and some that can affect power grids on Earth.

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But sunspot number isn’t the only indicator we see;

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these numbers are often combined with other signs.

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[Text: 2: Track location of sunspots]

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At the beginning of each cycle,

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sunspots appear on the Sun in the midlatitudes for a brief few hours to days.

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At solar minimum, there are often days without any spots at all.

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As the Sun becomes more active,

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sunspots form closer to the equator and can stick around for weeks to months.

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These sunspot patterns give clues to what drives the solar cycle —

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the twisting of the Sun’s magnetic field.

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Like Earth, the Sun has a magnetic field with a north and south pole.

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But unlike Earth, the Sun’s magnetic field becomes extremely complex.

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This is because the Sun is made of plasma —

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a charged gas that generates electric currents.

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As the Sun rotates, plasma around the equator moves faster than near the poles,

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causing the magnetic fields to become stretched, elongated and then twisted.

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Then Kinks in the magnetic fields burst through the surface

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as sunspots larger than the size of Earth.

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As the solar cycle unfolds,

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more sunspots appear and the magnetic field becomes more tangled.

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At the peak of the solar cycle, the Sun’s magnetic field flips —

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the north pole switches to the south and vice versa.

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The cycle then ramps down ready to start a new cycle.

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Scientists can eventually see the result of this flip within sunspots using satellites.

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[Text: 3: Spot new sunspots]

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This black and white image of the Sun shows the magnetic field on the surface.

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Most sunspots appear in pairs.

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Like a magnet, one side is positive and the other is negative.

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After they form, they gradually disappear again

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leaving behind remnants of magnetic fields that move towards the Sun’s poles.

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Eventually each pole accumulates enough magnetic fields forcing the Sun’s poles to flip at the peak of the cycle.

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Then new sunspot groups appear with the polarities in the opposite direction.

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Scientists look for a consistent string of these new sunspots in order to declare the next solar cycle.

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But the transition between cycles is slow and messy.

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Cycles often overlap creating freckles of old and new sunspots on the Sun at the same time.

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Scientists can only determine we’re in the new cycle when the number of new sunspots overtake old ones,

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which can be six months to a year after the new cycle has begun.

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While these spots give a visible tracker,

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in recent years scientists have discovered another signal that is hard to see from Earth.

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[Text: 4: Measure strength of Sun’s poles]

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The strength of the Sun’s poles during solar minimum

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can help predict how active the next cycle will be. 

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After the poles have reversed at the peak, scientists keep a close eye on it for the next few years.

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If the magnetic fields accumulated at the poles become strong during this time,

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it’s likely the next solar cycle will be an active one.

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If the buildup is weak, the next solar cycle won’t be as active.

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While we use these indicators to track the Sun, predictions are still hard.

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After all, we’ve only detailed satellite observations of the last four solar cycles

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and scientists are still learning about what causes the Sun’s cycle.

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So until we piece together those missing pieces,

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the Sun, even with its 11-year clock, will continue to surprise us.

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