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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00:00 There's a rhythm emanating from the Sun to the edges of the solar system.
00:04 Roughly every 11 years, our star ramps up to a turbulent state,
00:08 expelling violent eruptions.
00:10 After a peak, it comes down to a quieter phase
00:13 before starting all over again.
00:15 This is known as the solar cycle.
00:17 This ebb and flow of solar activity affects the entire solar system,
00:22 including spacecraft electronics and astronauts
00:25 that can be affected by particle radiation
00:27 if they're not sufficiently protected.
00:30 Understanding the solar cycle is one of the oldest problems in solar physics,
00:34 and now predicting it is more critical than ever
00:37 as we venture to the Moon, Mars, and beyond.
00:40 So here are ways we've learned about tracking it.
00:43 So welcome to the dome.
00:49 Today we're going to observe the Sun and see if it has some sunspots.
00:53 Every morning when the skies are clear,
00:55 Olivier looks through this telescope in search of sunspots.
00:59 These are dark blotches on the Sun that are the main source of solar eruptions.
01:03 They appear and disappear on the Sun's surface.
01:06 So we're not looking at the Sun.
01:08 In fact, we're looking at the shadow of the instrument.
01:13 Then we put the paper always at the same place,
01:18 and then we can start drawing.
01:21 Olivier and a team of Sun observers record the pattern of sunspots
01:25 by pencil.
01:26 The first known record of sunspots date back to around 1,000 years ago
01:30 in China.
01:31 After the invention of the telescope in the 17th century,
01:34 routine observations were made.
01:36 Today, sunspot drawers still use the same technique.
01:40 While we've created satellites that can see the Sun in much more detail
01:43 in recent decades, drawing by hand keeps the centuries-long record
01:47 consistent.
01:49 The sunspot number record goes back farther than any other instrument,
01:53 allowing scientists to analyze the Sun's behavior
01:55 over many, many solar cycles.
01:57 Sunspot numbers are collected from observatories around the world
02:01 and are averaged.
02:02 During every 11-year cycle, the number of sunspots
02:05 rise from zero to a peak and then go back down to zero again.
02:09 Scientists use these numbers to determine when a new solar cycle
02:13 begins and how active a cycle is.
02:16 Solar maximum, the period of highest activity,
02:19 can vary wildly from cycle to cycle.
02:22 The more sunspots there are, the higher the frequency
02:25 of solar storms of all types, some that create aurora
02:29 and some that can affect power grids on Earth.
02:32 But sunspot number isn't the only indicator we see.
02:35 These numbers are often combined with other signs.
02:39 At the beginning of each cycle, sunspots
02:41 appear on the Sun in the mid-latitudes for a brief few hours to days.
02:45 At solar minimum, there are often days without any spots at all.
02:49 As the Sun becomes more active, sunspots
02:51 form closer to the equator and can stick around for weeks to months.
02:56 These sunspot patterns give clues to what drives the solar cycle,
03:00 the twisting of the Sun's magnetic field.
03:03 Like Earth, the Sun has a magnetic field with a north and south pole.
03:07 But unlike Earth, the Sun's magnetic field becomes extremely complex.
03:11 This is because the Sun is made of plasma, a charged gas that
03:15 generates electric currents.
03:17 As the Sun rotates, plasma around the equator
03:20 moves faster than near the poles, causing the magnetic fields
03:23 to become stretched, elongated, and then twisted.
03:27 Then kinks in the magnetic fields burst through the surface
03:30 as sunspots larger than the size of Earth.
03:33 As the solar cycle unfolds, more sunspots appear,
03:36 and the magnetic field becomes more tangled.
03:39 At the peak of the solar cycle, the Sun's magnetic field flips.
03:43 The north pole switches to the south, and vice versa.
03:47 The cycle then ramps down, ready to start a new cycle.
03:50 Scientists can eventually see the result of this flip
03:53 inside sunspots using satellites.
03:55 This black-and-white image of the Sun shows the magnetic field
04:01 on the surface.
04:03 Most sunspots appear in pairs.
04:05 Like a magnet, one side is positive and the other is negative.
04:08 After they form, they gradually disappear again,
04:12 leaving behind remnants of magnetic fields
04:14 that move towards the Sun's poles.
04:16 Eventually, each pole accumulates enough magnetic fields,
04:20 forcing the Sun's poles to flip at the peak of the cycle.
04:24 Then new sunspot groups appear with the polarities
04:28 in the opposite direction.
04:29 Scientists look for a consistent string of these new sunspots
04:33 in order to declare the next solar cycle.
04:36 But the transition between cycles is slow and messy.
04:39 Cycles often overlap, creating freckles of old and new sunspots
04:43 on the Sun at the same time.
04:46 Scientists can only determine we're in the new cycle
04:49 when the number of new sunspots overtake old ones,
04:52 which can be six months to a year after the new cycle has begun.
04:56 While these spots give us a visible tracker,
04:58 in recent years, scientists have discovered another signal
05:01 that's hard to see from Earth.
05:04 The strength of the Sun's poles during solar minimum
05:07 can help predict how active the next cycle will be.
05:11 After the poles have reversed at the peak,
05:14 scientists keep a close eye on it for the next few years.
05:17 If the magnetic fields accumulated at the poles
05:20 become strong during this time,
05:22 it's likely the next solar cycle will be an active one.
05:25 If the buildup is weak,
05:26 the next solar cycle won't be as active.
05:30 While we use these indicators to track the Sun,
05:33 predictions are still hard.
05:36 After all, we've only had detailed satellite observations
05:39 of the last four solar cycles,
05:41 and scientists are still learning about what causes the Sun cycle.
05:45 So until we piece together those missing pieces,
05:49 the Sun, even with its 11-year clock,
05:51 will continue to surprise us.
05:54 [music]