How To Track The Sun's Cycle

Narration: Joy Ng


[00:00:00:000] There's a rhythm emanating from the Sun

[00:00:02:150] to the edges of the solar system.

[00:00:04:186] Roughly every 11 years, our star ramps up to a turbulent state expelling violent eruptions.

[00:00:09:276] After a peak, it calms down to a quieter phase,

[00:00:13:360] before starting all over again.

[00:00:15:960] This is known as the solar cycle.

[00:00:17:204] This ebb and flow of solar activity affects the entire solar system

[00:00:22:450] including spacecraft electronics and astronauts

[00:00:25:111] that can be affected by particle radiation if they're not sufficiently protected.

[00:00:29:201] Understanding the solar cycle is one of the oldest problems in solar physics

[00:00:34:207] and now, predicting it is more critical than ever as we venture to the Moon and Mars, and beyond.

[00:00:40:162] So, here are ways we've learned about tracking it.

[00:00:43:207] [Text: 1: Count sunspots]

[00:00:46:228] So, welcome to the dome.

[00:00:49:270] Today, we're going to observe the Sun

[00:00:50:249] and see if it has some sunspots.

[00:00:53:225] Every morning when the skies are clear,

[00:00:55:192] Olivier looks through this telescope in search of sunspots.

[00:00:59:138] These are dark blotches on the Sun that are the main source of solar eruptions.

[00:01:03:225] They appear and disappear on the Sun's surface.

[00:01:06:225] So, we're not looking at the Sun.

[00:01:08:162] In fact, we're looking at the shadow of the instrument.

[00:01:13:237] Then we put the paper always at the same place

[00:01:18:600] and then we can start drawing.

[00:01:21:150] Olivier and a team of sun observers record the pattern of sunspots by pencil.

[00:01:26:150] The first known record of sunspots date back to around a thousand years ago in China.

[00:01:31:030] After the invention of the telescope in the 17th century, routine observations were made.

[00:01:36:174] Today, sunspot drawers still use the same technique.

[00:01:39:294] While we've created satellites that can see the Sun in much more detail in recent decades,

[00:01:44:261] drawing by hand keeps the centuries-long record consistent.

[00:01:49:990] The sunspot number record goes back farther than any other instrument

[00:01:52:294] allowing scientists to analyze the Sun's behavior over many, many solar cycles. 

[00:01:57:168] Sunspot numbers are collected from observatories around the world and are averaged.

[00:02:02:228] During every 11-year cycle, the number of sunspots rise from zero to a peak

[00:02:07:168] and then go back down to zero again.

[00:02:09:192] Scientists use these numbers to determine when a new solar cycle begins and how active a cycle is.

[00:02:16:180] Solar maximum, the period of highest activity, can vary wildly from cycle to cycle.

[00:02:22:222] The more sunspots there are, the higher the frequency of solar storms of all types -

[00:02:27:156] some that create aurora and some that can affect power grids on Earth.

[00:02:32:258] But sunspot number isn't the only indicator we see;

[00:02:35:168] these numbers are often combined with other signs.

[00:02:38:180] [Text: 2: Track location of sunspots]

[00:02:39:129] At the beginning of each cycle,

[00:02:40:276] sunspots appear on the Sun in the midlatitudes for a brief few hours to days.

[00:02:45:138] At solar minimum, there are often days without any spots at all.

[00:02:49:129] As the Sun becomes more active,

[00:02:51:720] sunspots form closer to the equator and can stick around for weeks to months.

[00:02:56:330] These sunspot patterns give clues to what drives the solar cycle -

[00:03:00:630] the twisting of the Sun's magnetic field.

[00:03:03:240] Like Earth, the Sun has a magnetic field with a north and south pole.

[00:03:07:780] But unlike Earth, the Sun's magnetic field becomes extremely complex.

[00:03:11:297] This is because the Sun is made of plasma -

[00:03:14:360] a charged gas that generates electric currents.

[00:03:17:330] As the Sun rotates, plasma around the equator moves faster than near the poles,

[00:03:22:108] causing the magnetic fields to become stretched, elongated and then twisted.

[00:03:26:234] Then Kinks in the magnetic fields burst through the surface

[00:03:30:183] as sunspots larger than the size of Earth.

[00:03:33:600] As the solar cycle unfolds,

[00:03:35:114] more sunspots appear and the magnetic field becomes more tangled.

[00:03:39:990] At the peak of the solar cycle, the Sun's magnetic field flips -

[00:03:43:252] the north pole switches to the south and vice versa.

[00:03:46:228] The cycle then ramps down ready to start a new cycle.

[00:03:49:285] Scientists can eventually see the result of this flip within sunspots using satellites.

[00:03:56:030] [Text: 3: Spot new sunspots]

[00:03:58:138] This black and white image of the Sun shows the magnetic field on the surface.

[00:04:02:177] Most sunspots appear in pairs.

[00:04:05:660] Like a magnet, one side is positive and the other is negative.

[00:04:09:450] After they form, they gradually disappear again

[00:04:11:261] leaving behind remnants of magnetic fields that move towards the Sun's poles.

[00:04:16:243] Eventually each pole accumulates enough magnetic fields forcing the Sun's poles to flip at the peak of the cycle.

[00:04:24:210] Then new sunspot groups appear with the polarities in the opposite direction.

[00:04:29:168] Scientists look for a consistent string of these new sunspots in order to declare the next solar cycle.

[00:04:36:000] But the transition between cycles is slow and messy.

[00:04:39:165] Cycles often overlap creating freckles of old and new sunspots on the Sun at the same time.

[00:04:46:810] Scientists can only determine we're in the new cycle when the number of new sunspots overtake old ones,

[00:04:52:420] which can be six months to a year after the new cycle has begun.

[00:04:56:420] While these spots give a visible tracker,

[00:02:35:840] in recent years scientists have discovered another signal that is hard to see from Earth.

[00:05:03:183] [Text: 4: Measure strength of Sun's poles]

[00:05:04:120] The strength of the Sun's poles during solar minimum

[00:05:07:990] can help predict how active the next cycle will be. 

[00:05:10:273] After the poles have reversed at the peak, scientists keep a close eye on it for the next few years.

[00:05:17:300] If the magnetic fields accumulated at the poles become strong during this time,

[00:05:22:030] it's likely the next solar cycle will be an active one.

[00:05:25:960] If the buildup is weak, the next solar cycle won't be as active.

[00:05:30:840] While we use these indicators to track the Sun, predictions are still hard.

[00:05:35:111] After all, we've only detailed satellite observations of the last four solar cycles

[00:05:41:183] and scientists are still learning about what causes the Sun's cycle.

[00:05:45:198] So until we piece together those missing pieces,

[00:05:48:168] the Sun, even with its 11-year clock, will continue to surprise us.