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  • 30/06/2025
The 11-year solar cycle is tracked by NASA, learn how they do it.

Credit: NASA Goddard Space Flight Center
Transcript
00:00There's a rhythm emanating from the Sun to the edges of the solar system.
00:04Roughly every 11 years, our star ramps up to a turbulent state expelling violent eruptions.
00:10After a peak, it calms down to a quieter phase before starting all over again.
00:15This is known as the solar cycle.
00:18This ebb and flow of solar activity affects the entire solar system,
00:22including spacecraft electronics and astronauts
00:25that can be affected by particle radiation if they're not sufficiently protected.
00:29Understanding the solar cycle is one of the oldest problems in solar physics,
00:34and now predicting it is more critical than ever as we venture to the Moon, Mars and beyond.
00:40So here are ways we've learned about tracking it.
00:47So welcome to the dome.
00:49Today we're going to observe the Sun and see if it has some sunspots.
00:53Every morning when the skies are clear,
00:55Olivier looks through this telescope in search of sunspots.
00:59These are dark blotches on the Sun that are the main source of solar eruptions.
01:03They appear and disappear on the Sun's surface.
01:06So we're not looking at the Sun.
01:08In fact, we're looking at the shadow of the instrument.
01:13Then we put the paper always at the same place.
01:17And then we can start drawing.
01:21Olivier and a team of sun observers record the pattern of sunspots by pencil.
01:26The first known record of sunspots date back to around a thousand years ago in China.
01:31After the invention of the telescope in the 17th century,
01:34routine observations were made.
01:36Today, sunspot drawers still use the same technique.
01:40While we've created satellites that can see the Sun in much more detail in recent decades,
01:45drawing by hand keeps the centuries-long record consistent.
01:49The sunspot number record goes back farther than any other instrument,
01:53allowing scientists to analyze the Sun's behavior over many, many solar cycles.
01:57Sunspot numbers are collected from observatories around the world and are averaged.
02:02During every 11-year cycle, the number of sunspots rise from zero to a peak
02:07and then go back down to zero again.
02:10Scientists use these numbers to determine when a new solar cycle begins
02:14and how active a cycle is.
02:16Solar maximum, the period of highest activity, can vary wildly from cycle to cycle.
02:22The more sunspots there are, the higher the frequency of solar storms of all types.
02:28Some that create aurora and some that can affect power grids on Earth.
02:32But sunspot number isn't the only indicator we see.
02:35These numbers are often combined with other signs.
02:39At the beginning of each cycle, sunspots appear on the Sun in the mid-latitudes
02:44for a brief few hours to days.
02:46At solar minimum, there are often days without any spots at all.
02:49As the Sun becomes more active, sunspots form closer to the equator
02:54and can stick around for weeks to months.
02:56These sunspot patterns give clues to what drives the solar cycle,
03:00the twisting of the Sun's magnetic field.
03:03Like Earth, the Sun has a magnetic field with a north and south pole.
03:07But unlike Earth, the Sun's magnetic field becomes extremely complex.
03:12This is because the Sun is made of plasma, a charged gas that generates electric currents.
03:17As the Sun rotates, plasma around the equator moves faster than near the poles,
03:22causing the magnetic fields to become stretched, elongated and then twisted.
03:26Then kinks in the magnetic fields burst through the surface as sunspots larger than the size of Earth.
03:33As the solar cycle unfolds, more sunspots appear and the magnetic field becomes more tangled.
03:39At the peak of the solar cycle, the Sun's magnetic field flips.
03:43The North Pole switches to the south and vice versa.
03:47The cycle then ramps down, ready to start a new cycle.
03:50Scientists can eventually see the result of this flip inside sunspots using satellites.
03:56This black and white image of the Sun shows the magnetic field on the surface.
04:02Most sunspots appear in pairs.
04:05Like a magnet, one side is positive and the other is negative.
04:08After they form, they gradually disappear again, leaving behind remnants of magnetic fields that move towards the Sun's poles.
04:16Eventually, each pole accumulates enough magnetic fields, forcing the Sun's poles to flip at the peak of the cycle.
04:24Then, new sunspot groups appear with the polarities in the opposite direction.
04:29Scientists look for a consistent string of these new sunspots in order to declare the next solar cycle.
04:36But the transition between cycles is slow and messy.
04:39Cycles often overlap, creating freckles of old and new sunspots on the Sun at the same time.
04:45Scientists can only determine we're in the new cycle when the number of new sunspots overtake old ones,
04:52which can be six months to a year after the new cycle has begun.
04:56While these spots give us a visible tracker, in recent years, scientists have discovered another signal that's hard to see from Earth.
05:04The strength of the Sun's poles during solar minimum can help predict how active the next cycle will be.
05:11After the poles have reversed at the peak, scientists keep a close eye on it for the next few years.
05:17If the magnetic fields accumulated at the poles become strong during this time,
05:22it's likely the next solar cycle will be an active one.
05:25If the build-up is weak, the next solar cycle won't be as active.
05:30While we use these indicators to track the Sun, predictions are still hard.
05:35After all, we've only had detailed satellite observations of the last four solar cycles,
05:41and scientists are still learning about what causes the Sun's cycle.
05:45So until we piece together those missing pieces, the Sun, even with its 11-year clock, will continue to surprise us.
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