Understand 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

00:00There'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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