Learn How NASA Tracks The Solar Cycles

Space.com

The 11-year solar cycle is tracked by NASA, learn how they do it.   Credit: NASA Goddard Space Flight Center

Transcript

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]

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