The 11-year solar cycle is tracked by NASA, learn how they do it.
Credit: NASA Goddard Space Flight Center
Credit: NASA Goddard Space Flight Center
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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.
00:30Understanding the solar cycle is one of the oldest problems in solar physics,
00:35and 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.
00:46So 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, Olivier looks through this telescope in search of sunspots.
00:59These are dark blotches on the Sun that are the main source of solar eruptions.
01:04They appear and disappear on the Sun's surface.
01:06So we're not looking at the Sun. In fact, we're looking at the shadow of the instrument.
01:13Then we put the paper always at the same place, and then we can start drawing.
01:20Olivier and a team of sun observers record the pattern of sunspots by pencil.
01:25The first known record of sunspots date back to around 1,000 years ago in China.
01:30After the invention of the telescope in the 17th century, routine observations were made.
01:35Today, sunspot drawers still use this same technique.
01:38While we've created satellites that can see the Sun in much more detail in recent decades,
01:43drawing by hand keeps this centuries-long record consistent.
01:47The sunspot number record goes back farther than any other instrument,
01:51allowing scientists to analyze the Sun's behavior over many, many solar cycles.
01:55Sunspot numbers are collected from observatories around the world and are averaged.
02:00During every 11-year cycle, the number of sunspots rise from zero to a peak
02:05and then go back down to zero again.
02:08Scientists use these numbers to determine when a new solar cycle begins and how active a cycle is.
02:14The more sunspots there are, the higher the frequency of solar storms of all types,
02:19some that create aurorae and some that can affect power grids on Earth.
02:24But sunspot number isn't the only indicator we see.
02:27These numbers are often combined with other signs.
02:31At the beginning of each cycle, sunspots appear on the Sun in the mid-latitudes
02:35for a brief period of time, and then go back down to zero.
02:39At the beginning of each cycle, sunspots appear on the Sun in the mid-latitudes
02:43for a brief few hours to days.
02:45At solar minimum, there are often days without any spots at all.
02:49As the Sun becomes more active,
02:51sunspots form closer to the equator and 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,
03:14a 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.
03:27Then kinks in the magnetic fields burst through the surface
03:30as sunspots larger than the size of Earth.
03:33As the solar cycle unfolds, more sunspots appear
03:36and 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
03:53inside sunspots using satellites.
03:58This black and white image of the Sun shows the magnetic field on the surface.
04:03Most sunspots appear in pairs.
04:05Like a magnet, one side is positive and the other is negative.
04:09After they form, they gradually disappear again,
04:12leaving behind remnants of magnetic fields that move towards the Sun's poles.
04:17Eventually, each pole accumulates enough magnetic fields,
04:20forcing 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.
04:30Scientists look for a consistent string of these new sunspots
04:33in order to declare the next solar cycle.
04:36But the transition between cycles is slow and messy.
04:40Cycles often overlap,
04:41creating freckles of old and new sunspots on the Sun at the same time.
04:46Scientists can only determine we're in the new cycle
04:49when 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,
04:58in recent years, scientists have discovered another signal
05:02that's hard to see from Earth.
05:04The strength of the Sun's poles during solar minimum
05:07can help predict how active the next cycle will be.
05:11After the poles have reversed at the peak,
05:14scientists 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 buildup is weak, the next solar cycle won't be as active.
05:29While we use these indicators to track the Sun,
05:32predictions are still hard.
05:35After all, we've only had detailed satellite observations
05:38of the last four solar cycles,
05:40and scientists are still learning about what causes the Sun's cycle.
05:44So until we piece together those missing pieces,
05:48the Sun, even with its 11-year clock,
05:50will continue to surprise us.
05:59Transcribed by ESO. Translated by —