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Ask an Expert: Our Powerful Sun
Image of multiple solar flares Multiple solar flares on the sun. Credit: JAXA
Artist concept of a coronal massive ejection Artist concept of a coronal mass ejection. Credit: NASA
Aurora Borealis over Earth, seen from the International Space Station Aurora borealis, seen from the International Space Station. Solar winds help power these atmospheric displays. Image credit: NASA

More Information
Link: NASA Solar Physics
Link: Solar Cycle Prediction
Video: Solar Magnetism
NASA Worldbook: The Sun
Link: NASA's "Summer Science Camp"
Eight planets and their moons, tens of thousands of asteroids, and trillions of comets revolve around the sun. One of these is our Earth, orbiting the sun at an average distance of about 92,960,000 miles (149,600,000 kilometers). The sun is a huge, glowing ball that provides light, heat, and other energy to our Earth. But our beneficial space neighbor is also capable of some stellar "temper tantrums."

On Thursday, June 17, Dr. David Hathaway, a solar scientist at NASA's Marshall Space Flight Center, answered your questions about how our sun works and produces phenomena such as sunspots, solar flares, and solar storms -- "hot' topics that have communication and health implications for everyone on Earth.

Check back on this page on Monday for a complete transcript of today's chat.

More About Chat Expert David Hathaway

Dr. Hathaway received his doctorate in Astrophysics from the University of Colorado in Boulder, CO in 1979. He worked for two years as a Post-Doctoral Fellow in the Advanced Study Program at the National Center for Atmospheric Research before taking a 3-year position as an Assistant Astronomer at the National Solar Observatory site in Sunspot, NM. He came to NASA’s Marshall Space Flight Center in Huntsville, AL in 1984 where he has been a member of the solar physics group and served as its team leader from 1996 to 2010. He has written over 150 articles on the Sun and solar physics and has received three US patents. He has been the recipient of dozens of awards from within NASA and from the broader scientific community. Hathaway has served on numerous advisory committees as well as elected positions within scientific organizations.

Dr. Hathaway’s primary research interests include the nature and origin of the sunspot cycle and the fluid dynamics of the Sun’s interior. His research includes constructing computer models for flows on the surface of the Sun and analysis programs for extracting those flows from satellite observations. He maintains a database on sunspots, including their sizes and positions, that extends back to the year 1874. This database is widely used by the solar physics community. Data plots, images, and animations produced by Dr. Hathaway are also widely used in many publications by both his scientific colleagues and the scientific press.

Chat Transcript

(Moderator) Jason: Today's Chat is Scheduled to Begin at 3pm ET. Please begin to ask your questions by typing them into the box at the bottom of the screen and clicking the 'Ask' button on the right. We'll begin answering them in twenty minutes. Thanks for your patience.

(Moderator) Jason: Hello everyone. Our chat will begin momentarily. Please begin to ask your questions by typing them into the box at the bottom of the screen and clicking the 'Ask' button on the right. We'll begin answering them in a few minutes. Thanks for your patience.

Abishek: Can suns rays reach how more long than Pluto?

David: The sun's rays can reach 4.5 billion light years. Pluto is only three light hours from the sun.

Akarsh_Valsan: Sir, can you explain the major composition of the Sun?

David: The sun is composed of 70% hydrogen, 28% helium, and 2% carbon, oxygen, and nitrogen. This is the composition it was born with from the cloud of gas that it came from long ago.

chaosx: What truly is going to happen during our next solar cycle in 2013. Will it knock out much of the electronics in certain areas of the world?

David: The next solar cycle by most indications will be the weakest in 100 years. We also have satellites and other technology that can help us mitigate the problems associated with flares. However, so much of our technology is sensitive to space weather. We need better predictions and radiation-hardened electronic components.

abishek: Can aurora borealis seen from the earth?

David: Aurora borealis are formed when energetic particles from the sun stream down the Earth's magnetic field lines into the polar regions. It can be seen after many significant solar flares. We just had one last weekend.

g00nne: Hello, I wrote today, the message is probably lost somewhere. Can you tell me some information about the galactic Wednesday and consequent eruption of the Sun 2013? Thank you for your reply.

David: The next solar cycle should reach its peak in mid-2013. Again, we're expecting the weakest solar cycle in 100 years, so the effects should be less than what we've seen in the last few solar cycles.

nomaanakhtar: Do solar flares produce solar winds?

David: Solar flares are huge explosions on the surface of the sun. They typically last anywhere from a few minutes to a few hours and can blast a billion tons of matter off of the sun. The solar wind is something altogether different. The solar wind blows off of the sun at all times, with typical speeds of about 1 million mph. We still don't know exactly what causes the solar wind, but we know that it's related to the sun's 1 million degree corona, or outer atmosphere.

Feign: Does the increase of solar flares happen approximately once a decade, and is this increase in flares any different from previous times?

David: The frequency of solar flares rises and falls with the sunspot cycle, which is about 11 years long. The bigger cycles have more flares than the smaller cycles. Nonetheless, a small cycle can produce a really nasty flare!

Feign: Is a large solar flare capable of destroying life on Earth?

David: No. :) The sun has been producing solar flares for 4.5 billion years, and we're still here.

prat: I read that earth's magnetic field is protection us from solar flares. Is it true? ANd how does it protect? What is the actual phenomena?

David: Yes, that's true. The energetic particles produced by solar flares are electrically charged particles that are diverted by magnetic fields. We're also protected by our atmosphere which blocks all but the most energetic particles.

Adam: Hello Jason and David. My question related to solar variability. I'm interested to hear David Hathaway's opinion on the effect that solar variability has on the climate here on Earth. There is a school of thought amongst climate change skeptics that the warming experienced on Earth over the last 150/200 years can be attributed to an increase in solar activity and I am wondering whether David believes that this idea fits the data. Thanks for your time.

David: There do appear to be connections between solar activity and climate. The sun is actually 0.1 % brighter at sunspot cycle maximum than at minimum, but this should only produce about 1/10 degree C change in temperature. The apparent effect is larger than this, but we don't know the exact connection. One possibility is that the sun's ultraviolet light, which varies by 3-4% at sunspot cycle maximum, might influence the Earth's upper atmosphere. Another possibility is cosmic rays, which have higher fluxes at sunspot cycle minimum might produce clouds. We still don't know the full answer on this, but our best estimates are that the sun's contribution to global warming plays a minor role.

nomaan: What are solar flares?

David: Solar flares are explosions produced by twisted magnetic fields in the sun's atmosphere. They produce the energy equivalent of about 1 million megatons of TNT.

nyswimmer: How hot is the sun?

David: The sun is 5,770 degree Kelvin or about 10,000 degrees F at the surface, but it has temperatures of tens of millions of degrees in its core where hydrogen is being converted into helium.

(Moderator) Jason: We're working to get through all of the great questions you've asked us. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Richard_Hendricks: How "prepared" are humans for a severe solar storm?

David: We're better prepared now than we have been, but our technology is more sensitive to the effects of solar storms. We have two satellites, ACE and WIND, that are a million miles upstream in the solar wind and provide us with about a one-hour advanced warning of the magnetized clouds of material blown off of the sun by solar flares. This is enough to allow satellite operators and electrical power distributors to adjust equipment in anticipation of the impending impact.

K4DXV: What is your best guess for the peak of cycle 24?

David: My current estimate has a smoothed sunspot number of about 70. The last sunspot cycle had a peak of about 120, and the two before that had peaks of about 160.

jjordan10: About how much energy is produced by our sun in a year?

David: The Sun provides about 1,300 watts per square meter every second to the Earth. Multiple that by the area of the Earth and number of seconds in a year. This is left as an exercise for the student. :)

Ediz_Celik: What is the source of solar storms ? :-)

David: solar flares are one source of solar storms. Two other eruptions from the sun can also produce solar storms: coronal mass ejections and filament eruptions. CMEs are huge clouds of magnetized gases that are blown off of the sun. Filaments are denser clouds of material that can also escape from the sun. Flares, CMEs and filament eruptions can all occur together or they can occur independently.

Feign: What is the strangest thing you have witnessed or catalogued the sun doing?

David: Going through this REALLY long minimum. I was fully expecting a quick end to the last cycle and the beginning of a large sunspot cycle. This long minimum left behind a sunspot cycle more than 12 years long, with a minimum lower than we've seen in 100 years. I wasn't expecting that, but I'm ready for it now!

nomaan: What is the corona of the sun?

David: The sun's corona is its outer atmosphere that's usually only seen during a total eclipse. We now have instruments that produce artificial eclipses all the time. The corona is exceedingly hot, over 1 million degrees C, while the surface is "only "about 6,000 degrees C. We think the corona is heated by mechanisms involving its magnetic field. We're still arguing about the details.

abishek: Will our sun become a black hole?

David: No, the sun just isn't massive enough to produce a black hole. The sun should leave behind a white dwarf. If more massive, it might leave behind a neutron star. It takes a star about 10x as massive as the sun to produce a black hole.

ramneek: What exactly constitutes coronal mass?

David: A coronal mass ejection (CME) is a blob of plasma (ionized material) with an embedded magnetic field. They travel through the solar system on the solar wind in speeds in excess of 1 million mph.

nomaan: What are geomagnetic storms?

David: They occur when disturbances in the solar wind strike the Earth's magnetic field. These disturbances can include coronal mass ejections and high-speed streams from solar coronal holes. When they strike the Earth's magnetic field, the magnetic field at the surface of the Earth can be seen to fluctuate. These fluctuations have been measured since 1844 and provide estimates of solar activity since that time.

Feign: How long do solar storms generally last?

David: Typical flares last for hours, but their effects can last for a day or more. Often flares occur in groups where a particularly active region on the sun may flare for several days.

(Moderator) Jason: We're still working on answering all the great questions you've asked. If you haven't seen yours yet, give us a few minutes to get to all of your questions. To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Tavish_DeGroot: Kind of the opposite of the risks from solar maximum, are there any risks to satellites during solar minimum?

David: Great question. During solar maximum, satellites are subjected to energetic particles from solar flares. During minimum, they receive a higher dose of galactic cosmic rays that can also cause damage.

Richard_Hendricks: The Earth's magnetic field is stable over fairly long times. Why does the sun's reverse every 11 years? Is it because of the slower rotation, or the energy injected by fusion?

David: The Earth's magnetic field flips randomly on time scales of 100,000 to 1 million years. The sun's magnetic field flips "fairly" regularly every 11 years. The major difference does have to do with the rotation. The sun rotates once every 27 days and the convective motions associated with its magnetic dynamo also have a time period of about 27 days. For the Earth, the rotation is one day, and the convective motions are much slower. This produces a very different magnetic dynamo for the earth.

ramneek: What causes reduced surface temp that gives rise to sunspots?

David: Sunspots are places where very strong magnetic fields loop up out of the sun. The magnetic fields in sunspots are strong enough to inhibit the flow of gases inside the sun. This effectively chokes off the heat flow below sunspots, making them darker and cooler than their surroundings.

K4DXV: Any ideas on why cycle 24 seems to be getting off to a slow, perhaps even herky-jerky, start?

David: Yes, I have my pet theory related to recent observations I made with a summer intern, Lisa Rightmire. We found that the sun's meridional flow, a flow from the equator to the sun's poles along meridian lines, was faster on the approach to this minimum than it was at the last minimum. Models for the transport of magnetic field by this flow indicate that this would produce a weak magnetic field at the sun's poles. This magnetic field is thought to be the source of the next sunspot cycle. Small sunspot cycles typically start late and leave behind a low solar minimum -- just what we observed.

Richard_Hendricks: How much variance do we see over time in solar analogues?

David: Solar analogues are other stars like the sun in which we can see starspot cycles. They show a wider range of activity than we typically see with the sun. Some of this may be due to differences in age or rotation rate. Some may also be due to periods of hyperactivity and grand minima. The sun went through the Maunder minimum, a grand minimum, from 1645-1715, a period of 70 years almost entirely free of sunspots.

Akarsh_Valsan: Can you give me more details about particle radiation?

David: Energetic particles from solar flares include protons, electrons, and the nuclei of other elements such as helium and carbon. They can travel at speeds approaching the speed of light. These particles can cause damage to electronics on satellites.

Ediz_Celik: If our galaxy collided with Andromeda, is there any possibility to our sun will collide with a star?

David: Star collisions are exceedingly rare in our position on the outskirts of the Milky Way galaxy. The sun is four light seconds in diameter, and the next star is four light years away. That should give an indication of how much space there is between stars!

Adam: In answer to abishek's question, you say the Sun's rays can travel for 4.5 billion light years. Can I ask how you came to this number? Surely the suns rays will continue indefinitely unless absorbed or reflected?

David: The sun has only been shining for 4.5 billion years.

1st_in_alphabetical_order: Is there anything on earth that can reach temperature of the sun surface without melting?

David: Not that I know of, unless you have some "unobtainium." :)

nyswimmer: What technology do you use to help you with your job?

David: I use observations from satellites and I use the Internet extensively. Without either of these, my job would be nearly impossible.

abishek: Which is hotter, Earth's core or the solar flares?

David: I believe the Earth's core is only a few 10,000 degrees. Solar flares can have temps in excess to 10 million degrees.

pdove: Can solar winds be used to propel spacecraft?

David: Actually, sunlight itself is better than the solar wind for propelling spacecraft. Solar sails are in active development but they use sunlight rather than solar wind.

Richard_Hendricks: How about a more relevant question: Could a solar flare cause a mass extinction? Actually, that's a terrible question. Given what we know about flare statistics, what's the strongest one we have seen, and what's the strongest one we would *expect.*

David: The sun has almost certainly been producing solar flares throughout 4.5 billion years. The mass extinctions we know about don't appear to have been caused by solar flares. So my suspicion is that solar flares aren't energetic enough to cause mass extinctions.

Mestre: Do paleo-records, like ice core samples and tree rings, record solar activity over long periods of time?

David: Excellent question and yes, they do. Galactic cosmic rays are modulated by the solar cycle. When the sun is more active, fewer cosmic rays reach earth. The cosmic rays can produce radioactive isotopes in the Earth's upper atmosphere. In particular, carbon-14 and berylium-10. The c-14 gets caught in tree rings, and the Be-10 gets trapped in ice. By looking at these isotopes, we can estimate levels of solar activity over the last 10,000 years.

BriGuy: Is it true that our Earth is overdue for a magnetic polar shift (where north becomes south and vice versa)? What will be the expected impact of such a thing, especially with the temporary loss of our protective magnetosphere?

David: The Earth's magnetic pole flips chaotically so it's hard to say when we're due for a shift. All indications are that this process takes a significant amount of time, so I wouldn't worry about it in my lifetime. Nonetheless, you raise an interesting question about our protective magnetosphere. If the polar shift is more than just a shift, but rather a loss of the Earth's magnetic field, then we'd lose this protection -- but we'd still have the atmosphere and its protection.

jamesdmendenhall: If the gas were removed, what solids would remain in our sun?

David: The sun contains all of the elements that we also have on Earth, but with the exception of hydrogen and helium, they're minor constituents. At the temperatures we see in the sun, all of these elements would remain as ionized gases and wouldn't solidify.

Akarsh_Valsan: Why does the sun appear yellowish during sunrise and as dark red during sunsets? Why is the sun changing its colour?

David: The sun's color remains yellowish at all times. The colors you see at sunrise and sunset are due to scattering of sunlight in the Earth's atmosphere.

sayyam: I listened in on a lecture from an astronomer that solar radiations react with the oxygen in ice present on poles to form carbon-14? what reaction takes place? And what is its relation with sun spots?

David: Cosmic rays produce carbon-14 (C-14) when they strike nitrogen in our atmosphere. The C-14 then acts like carbon and gets taken up by plants. So we see the C-14 in tree rings as indicators of previous solar activity.

enoch: Mr. David, are the flares actual fire or an typoe of electro magnetic waves?

David: Flares are magnetic explosions. The intense magnetic fields that loop up out of the sun in sunspots can become twisted and basically short-circuit themselves. It's called "magnetic reconnection." This process can release tremendous amounts of energy in a matter of seconds. The energy itself is seen in particles (electrons, protons) streaming out of the flaring region. There's also a great deal of light in the form of X-rays that is emitted by these particles.

prat: How does scientists predicts sun's age (the amount of fuel in it )?

David: Our best estimates of the sun's age actually come from meteorites, but we can also estimate it from our models of how the sun burns hydrogen to form helium. This actually sets a limit on how old the sun can get, about 9 billion years.

nyswimmer: Is it true that Venus is hotter than the sun?

David: No, the surface of Venus is about 700 degrees F. The surface of the sun is more than 10X that.

Tavish_DeGroot: What do you think is the most interesting aspect of the sun to study or observe?

David: The sun's magnetic field is the source of all interesting things about the sun. :) It's associated with the sunspot cycle, with solar flares, and with the hot corona and solar wind. So observing the sun's magnetic field -- how it's produced and behaves -- is most interesting to me.

jjordan10: How much cooler is a sunspot to the temperature of the surface of the sun?

David: The temperature in sunspots drops to about 3,000 degrees Kelvin, This is actually cool enough for molecules to form, titanium oxide in particular.

nomaan: Can solar flare of 2013 set any satellite out of orbit?

David: When the sun is active, it produces excess ultraviolet light that heats up the Earth's outer atmosphere and makes it expand. This produces drag on satellites in low Earth orbit and can cause them to de-orbit prematurely. Since we're expecting a small sunspot cycle maximum in 2013, we have the opposite problem in that we can't get rid of the space junk in low-Earth orbit.

1st_in_alphabetical_order: Do you like your job?

David: This is the job I wanted since I was 12 years old. I look forward to coming to work every morning and sometimes sneak in on weekends...and I actually get paid to do it!

(Moderator) Jason: We've got time for just a couple more questions. Thanks to everyone for participating today.

JFHeins: How can we know anything about the inner structure of the sun? Is that all deduced from computer simulations?

David: For the last 50 years, we've noticed waves on the surface of the sun that we now recognize as being sound waves trapped inside the sun. We can use these sound waves to probe the sun's interior the same way that geologists use seismic waves to probe the inside of the Earth. We also have very detailed physical models for the behavior of material inside the sun and a good understanding of the physics involved in making stars.

enoch: What is solar wind?

David: The solar wind consists of material from the surface of the sun that's heated and accelerated to speeds of about 1 million mph. It flows in all directions off of the sun and streams through the solar system well past the orbit of Pluto.

sayyam: How will be the sun after 5 billion years?

David: After another 5 billion years, the sun should have exhausted its supply of hydrogen in its core. The core then starts to collapse and becomes very hot, causing the outer layers to expand and create a red giant big enough to swallow up the inner planets (Mercury, Venus, and yes, sadly, Earth.)

orion: Do sun activities contribute at all to producing earthquakes and volcanoes here on earth?

David: Probably not. There's very little gravitational effect and certainly earthquakes and volcanoes are more prone to gravity.

jjordan10: Can everyday appliances be affected by the sun's energy?

David: Anything that relies on satellites can be affected by solar storms. This includes cable television, communications, weather satellites -- but for the most part, not things like cell phones or your toaster.

enoch: What is the medium for the magnetic waves to travel through the vacuum?

David: Space isn't a vacuum. The solar wind permeates the entire solar system and carries with it clouds of material within embedded magnetic fields.

JFHeins: Why is there granulation on the sun's surface?

David: Granulation is a pattern of convection cells seen at the surface of the sun. The cells are about 1,000 kms wide, and this is about the depth at which the pressure at the surface doubles. The pattern is caused by the cooling of the gases at the surface which are finally in a place where radiation can escape to space.

(Moderator) Jason: And now for the last question of this chat...

1st_in_alphabetical_order: It would be an honor if I could have the last question. Are the NASA cuts going to hinder your future sun research?

David: The science side of NASA is pretty healthy. We just launched the Solar Dynamics Observatory and are looking forward to many years of interesting research.

(Moderator) Jason: Thanks to everyone who posed questions today. We hope you found this to be very interesting and that you got some great answers. Join us next week as we continue our virtual summer science camp. We're talking about Eclipses. More info at:

(Moderator) Jason: And a big thanks to David for answering all your questions.

David: My pleasure -- thanks, everyone!

Janet Anderson, 256-544-0034
Marshall Space Flight Center, Huntsville, Ala.