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Seasons of the Sun

Season 1Nov 9, 2020

As Earth makes its annual trip around the Sun, we feel the impacts of its journey in the form of seasons. Our planet’s tilt in relation to the Sun determines what season we experience here on Earth. But, did you know that the Sun goes through seasons too? Delores Knipp, Dean Pesnell and Sabrina Savage explain.

NASA's Curious Universe

NASA’s Curious Universe

Episode Title: “Seasons of the Sun”

Release Date: Monday, Nov. 9

Run Time: 20 minutes

About the Episode:

As Earth makes its annual trip around the Sun, we feel the impacts of its journey in the form of seasons. Our planet’s tilt in relation to the Sun determines what season we experience here on Earth. But, did you know that the Sun goes through seasons too? Delores Knipp, Dean Pesnell and Sabrina Savage explain.


SABRINA SAVAGE: Without the Sun, we would not be talking today and no one would be able to listen while drinking coffee or a cup of juice. We couldn’t go to work. We couldn’t go to school. Because the Sun is ultimately the source of all of the energy in our solar system and in us even.

SABRINA SAVAGE: But it can also be the source of destruction if we don’t pay close attention. Most days the Sun appears to be happily hovering over us, providing warmth and light, but it does have this bit of a mean streak, if you will…

SABRINA SAVAGE: The Sun is very dynamic. It’s constantly changing. And when you zoom in on it and stare at it, it almost looks like it’s breathing.

NASA's Curious Universe

HOST PADI BOYD:This is NASA’s Curious Universe. Our universe is a wild and wonderful place. I’m Padi Boyd, and in this podcast, NASA is your tour guide!

HOST PADI BOYD:As Earth makes its annual journey around the Sun, we experience that journey in the form of seasons.

HOST PADI BOYD:Earth’s tilt in relation to the Sun determines what season we experience here on Earth. But did you know that the Sun goes through seasons, too?

HOST PADI BOYD:The Sun doesn’t have seasons like you and I experience. Its seasons of activity come and go every 11 years or so… in what’s called “the solar cycle.”

SABRINA SAVAGE: ..If you’ve ever been around a toddler, you’ve probably experienced how they have bursts of playful activity followed by complete crashes often with a meltdown in between, right before they finally give up and fall asleep on the floor right next to their bed. This will repeat the next day and the next day and the next always leading up to nap time. And sometimes the meltdowns are mild and other times there’s lots of screaming and tears.

HOST PADI BOYD:That’s Sabrina Savage. She’s a solar physicist at NASA’s Marshall Space Flight Center and she studies what it means to live with a star.

HOST PADI BOYD:Just like a toddler, the Sun has highs and lows. Sometimes the Sun is very active with random bursts of activity and at other times, it’s quiet. But, over the span of a decade, there IS a distinctive pattern on the Sun that scientists can follow.

HOST PADI BOYD: The active period is known as solar maximum. This is when there is lots of activity happening on the Sun, such as solar flares and sunspots. When the Sun is in its quiet phase, it is said to be in solar minimum. During this time, there is less activity and the Sun is pretty calm.

HOST PADI BOYD:Recently, scientists announced that our Sun has entered a new solar cycle–Solar Cycle 25. This means it’s the 25th solar cycle we’re monitoring since regular records began in 1755.

SABRINA SAVAGE:..We just recently moved over to a new solar cycle, which is quite exciting. The last cycle was fairly mild and many experts who model these global flows and activity trends, expect that the new one to be similar and to be fairly mild. But that does not mean that we are in the clear at all, large eruptions can happen at any time.

HOST PADI BOYD:To us, the Sun and the stars appear calm as they twinkle in the sky. But the surface of the Sun is anything but tranquil.

SABRINA SAVAGE:…the Sun is made entirely of plasma. It isn’t solid. And so it doesn’t all rotate together. Uh, the Sun actually spins faster at the equator than it does towards the poles…

SABRINA SAVAGE:And this plasma of ionized particle soup creates very large magnetic fields that actually wrap around the whole Sun, below the surface.

HOST PADI BOYD:As the plasma particle soup churns, electric currents create magnetic fields.

HOST PADI BOYD:At home, when you put a magnet on the fridge, it’s held in place by a magnetic force that comes from moving electric charges. As the electric charges move, they create magnetic fields.

HOST PADI BOYD:These magnetic fields twist around the Sun like big, magnetized rubber bands. Imagine twisting the middle of a rubber band faster than the ends.

HOST PADI BOYD:When you let go, the middle will spin faster and drag the ends of the band with it. This is also what happens on the Sun.

SABRINA SAVAGE: ..Things get messy really quickly. there’s bound to be some twisting and tangling and breaking. And in essence, the plasma that created the field also ends up tearing it apart. In some of the messy places, where those knots begin to form, magnetic fields are able to bubble up through the surface and form sunspots.

HOST PADI BOYD:Intense magnetic fields that manage to poke through the surface appear as dark blotches on the Sun. We call them sunspots. These are areas of high magnetic activity that can be up to ten times bigger than Earth!

HOST PADI BOYD: In visible light, which is what we see with our eyes, sunspots appear darker than the area around them. However, it’s a little bit more complicated than that up close.

SABRINA SAVAGE:You’ll see all of these writhing connected magnetic field lines and all of this plasma traveling along those fields. And it just looks like it’s pulsing the whole time. And that’s because of all of the, uh, the convection underneath the surface that’s causing that and moving all that plasma together. It’s really quite a beautiful thing.

SABRINA SAVAGE:And so very roughly speaking, it takes about 11 years, give or take, for the Sun to cycle from a smooth, quiet global magnetic field where there aren’t that many sunspots on the disc to one that is experiencing a lot of activity with a bunch of sunspots and a lot of eruptions at any given moment. So it’s all due to magnetic fields.

HOST PADI BOYD: How many sunspots appear on the Sun plays an important role in the solar cycle. They show scientists when a new solar cycle is starting and when there may be more activity from our star.

DEAN PESNELL:..So the Sun has some kind of seasons on it, that are related to the number of sunspots that are visible on the surface.

HOST PADI BOYD:That’s Dean Pesnell, he’s the project scientist for the Solar Dynamics Observatory at NASA’s Goddard Space Flight Center.

DEAN PESNELL:So a sunspot appears to be a dark region on the surface of the Sun..They’ve been regularly observed since the early 1600s, when people developed the first telescopes. But they have been recorded for about 3000 years…

HOST PADI BOYD:The history of sunspot counting goes back centuries. Scientists today count sunspots almost the same way as they did 200 years ago. If you brought an 18th century astronomer to a modern observatory, they would still be able to count the spots!

HOST PADI BOYD:Today’s satellites and high- powered telescopes are great for figuring out how the Sun works. However, when it comes to counting sunspots, we stick to the centuries-old method. That’s because modern telescopes are just too accurate.

DEAN PESNELL: The problem with the modern cameras is they see spots that are much smaller than a human would have seen 200 years ago using the telescopes that they had.

HOST PADI BOYD:We want to be able to keep using that long record of sunspot data and that means consistent measuring.

HOST PADI BOYD:Every day, all around the world, solar observers count sunspots by physically drawing a map of the Sun. With a pencil and paper, they are able to trace sunspots using the Sun’s light.

DEAN PESNELL:They have a telescope and they put a piece of paper into a little binder clip that they have there. And then they shine the Sun on to it and they make a couple adjustments. And then the person basically draws, they trace over what they see projected onto that piece of paper.

DEAN PESNELL:And then once that’s done, they take a piece of paper and they put it, take it away from the Sun and put it over someplace else. And then they go through and they count the number of Sunspots, they see and then they actually group them into families. And then that becomes the first official sunspot number of that day.

HOST PADI BOYD:Sketching out sunspots may seem like a pretty simple task, but it can be tricky when the Sun has lots of sunspots during solar maximum and the people sketching sunspots need to work quickly.

DEAN PESNELL:They need to finish this in a certain short period of time to make sure it’s the same kind of sampling. And you can just see them sketching furiously, trying to make it from one side of the Sun to the other, to pick up all the details that they can see with the human eye…

DEAN PESNELL:But we see much more detail now with our telescopes. So we rely on these hand-produced diagrams to do the sunspot number, even as we use the more precise and more accurate data to figure out what’s actually happening to produce sunspots and where they go.

HOST PADI BOYD:That sunspot number is very important for charting the solar cycle. But the number of sunspots isn’t the only important measurement.

HOST PADI BOYD:There are several ways to track solar cycle progress, such as the location of the sunspots themselves.

SABRINA SAVAGE: So as the cycle progresses, the sunspots begin to appear closer and closer to the equator. And so if you map out where the sunspots appear over time, it looks a lot like a butterfly with its outstretched wings outlined by where the sunspots first appear, moving from the poles to the equator.

SABRINA SAVAGE:And we call this a butterfly diagram because we’re very clever. These butterflies overlap a little bit, which makes it tricky to firmly announce a brand new cycle.

HOST PADI BOYD:Scientists keep track of sunspots to determine when there will be other types of solar activity.

HOST PADI BOYD:That’s because huge solar explosions often originate from sunspots.

HOST PADI BOYD:We keep a close watch on the Sun and its cycles because the Sun’s outbursts can impact our technology on Earth.

HOST PADI BOYD:The most famous of these solar storms happened in 1859.


HOST PADI BOYD: British astronomer Richard Carrington peered through his telescope and saw a bright, dazzling light blazing from a dark region on the Sun..

DELORES KNIPP:Shortly thereafter, there were great Aurora, Aurora so bright, that people at mid latitudes could actually read newspapers by them. So that is what we call the Carrington storms.

HOST PADI BOYD:That’s Delores Knipp (Kuh-nip). She’s a research professor at the University of Colorado, Boulder, and her area of study is space weather…

HOST PADI BOYD:She studies how the Sun’s activity affects the solar system, which includes us, here on Earth, too.

HOST PADI BOYD:The magnetic storms that the Sun sends out can have dramatic effects on Earth. The Carrington Event was so powerful, it lit the skies with bright aurora as far south as Puerto Rico and sent floods of electric currents that threw telegraph networks into disarray.

DELORES KNIPP:The Carrington event is the event where we had our first intersection between a great solar storm and a technology that we had become very dependent on. And that technology was the telegraph.


DELORES KNIPP: What came with that was the absolute garbling of telegraph signals worldwide. And that went on for many hours.


DELORES KNIPP:I believe it’s important to know how this episodic and cyclical nature of the Sun’s extreme behavior can impact society.

DELORES KNIPP:We are a very large, globally connected society that relies heavily on technology. And there are ways that this technology can be interrupted very quickly and very globally, by the Sun and its eruptions.

HOST PADI BOYD:These impacts are the result of powerful solar eruptions known as solar flares and coronal mass ejections.

DEAN PESNELL: So it’s not just sunspots. It’s all these other things that are related to the sunspots that go with the solar cycle that make it interesting to study.

HOST PADI BOYD:Solar flares are sudden outbursts of electromagnetic energy. These bright flashes can last from a few minutes to a few hours, kind of like fireworks on the Sun.

DEAN PESNELL: There are the things that the Sun does to get rid of the magnetic field. The magnetic field has gotten so strong, it actually is converted into heat and we get a big bright flash of light, called a solar flare.

DEAN PESNELL:But the Sun still has magnetic fields sticking above the surface that it would like to get rid of. And it does that by throwing the field off in what we call coronal mass ejections.

HOST PADI BOYD:These coronal mass ejections mean serious business. As the Sun churns and appears to breathe, it can hurl particles into space like a great, big sneeze.

SABRINA SAVAGE:…So when it sneezes, it could throw off mountains of material traveling at hundreds of miles per second, through interplanetary space. And that happens to be where we live.

HOST PADI BOYD:That material can’t pass through Earth’s atmosphere to hurt us down on the ground, but – at its very worst – it can affect our technology.

DEAN PESNELL: The coronal mass ejections, as they pass by the earth can interact with the Earth’s atmosphere and with the Earth’s magnetic field, to cause the aurora and to cause outages in things like power stations. They can interfere with communications that use radio waves.

DEAN PESNELL:We have a couple of examples later on in history where one of these coronal mass ejections actually affected something here on the Earth. The most famous is the one in March of 1989, which affected the eastern parts of the United States and Canada by taking out the power transmission lines, and so it caused power blackouts in parts of the eastern seaboard, the United States and Canada.

DELORES KNIPP:The March ’89 event was a one-two punch, that actually set up our power grid it seems for more of a disturbance than we were anticipating. While the eruptions occurred on different days, the arrival of the material seems to have happened on the same day. And so, Earth’s system, its atmosphere, its magnetosphere, its sphere of charged particles that surround Earth really did not have time to recover between the first event and the second event.

HOST PADI BOYD:The 1989 event showed the world that we need to prepare for solar storms. These disruptive events are not a matter of if they will happen again, but when.

SABRINA SAVAGE:And this is becoming a growing problem. If you think about it, as we become completely dependent on technology, especially our space assets and these, uh, coronal mass ejections can wreak havoc on communication, satellites, GPS, and power grids…

DELORES KNIPP:So now it becomes kind of imperative for scientists who are looking at this going — “Okay, what could happen next? What ways does nature find to disrupt our new favorite, absolutely essential technology?”

SABRINA SAVAGE: So understanding what drives the Sun and how to anticipate these outbursts are extremely important, especially as we become increasingly reliant on satellite communication and continue to expand beyond the Earth’s own protective magnetic field.

HOST PADI BOYD:While scientists have been able to unlock many of the Sun’s mysteries, there are still questions left to answer. From the first solar spacecraft Helios to the recently launched Solar Orbiter, NASA has a long history of studying the Sun.

SABRINA SAVAGE:We now have eyes constantly staring at the Sun with extraordinary resolution. At least one picture has been taken of the Sun every second for the last decade. And we never stop detecting the particles that it’s constantly throwing at us. We really see every blemish, we hear every sneeze and we are just at the very beginning of building up the baseline of these extraordinary observations that we need to cover at least one solar cycle and beyond. So we really are at the precipice of understanding what makes the Sun a variable star

SABRINA SAVAGE: The Sun is such an ingrained part of our lives. We don’t even think about it. We take it completely for granted. Uh, it’s just there, but it’s a star. So we look in awe and wonder at the sky at night because of how it glitters. At least I do. It makes us think of how small we are and how much of the universe there is out there. Uh, but we really should be just as introspective of the daytime sky.

HOST PADI BOYD:Without the Sun, we would not be here today. It’s so much more than a bright light in the sky. Our Sun supports life on Earth, but it also has an unpredictable side that makes it important to study.

HOST PADI BOYD:Over the years, we’ve learned a lot about our star. But there’s still so much we don’t know yet, and that’s why scientists like Sabrina, Dean and Delores are so interested in studying the Sun.

HOST PADI BOYD:Next time you step outside on a sunny day, maybe you will think a little more about the power and mysteries of our neighborhood star.


HOST PADI BOYD:This is NASA’s Curious Universe. This episode was written by Joy Ng, Lina Tran, and Vicky Woodburn. The Curious Universe team includes Maddie Arnold, Micheala Sosby, and Margot Wohl. Our executive producer is Katie Atkinson.

HOST PADI BOYD:Special thanks to Karen Fox, the Heliophysics team and Ryland Heagy.

HOST PADI BOYD:To keep up with the latest solar cycle science from NASA, check out

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