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Ask an Expert: All About the Sun!
Coronal loops, seen by the TRACE satellite Coronal loops on the sun. (M. Aschwanden et al. [LMSAL], TRACE, NASA)
Coronal Mass Ejection, seen by SOHO Coronal mass ejection. (SOHO Consortium, ESA, NASA)
Sunspot group, seen on Sept. 22, 2000 The sunspot group of Sept. 22, 2000. (SOHO, ESA & NASA)
View of solar prominences, seen by during Skylab 3 mission, 1973. Solar prominences, seen during Skylab 3 mission, 1973. (NASA/MSFC)

More Information
Link: NASA Solar Physics
Link: Solar Cycle Prediction
Video: Solar Magnetism
NASA Worldbook: The Sun
Link: Solar Week
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. The world is observing Solar Week from Oct. 18-22, 2010 -- a great time to learn more about our sun and how it affects our solar system.

On Thursday, Oct. 21, Dr. David Hathaway, a solar scientist at NASA's Marshall Space Flight Center, answered your questions about our sun: how it works, why it has cycles and how it produces solar phenomena -- such as sunspots, solar flares and solar storms.

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

David: Hi everyone, we're starting in a few minutes. Thanks for joining today's chat! Looking forward to your questions.

(Moderator Jason): Welcome to today’s Web chat with NASA scientist David Hathaway. Today’s topic, in honor of Solar Week, is about our powerful sun: why it behaves like it does, what powers it, and how it affects us on Earth. Please remember to stay on topic! This is a moderated chat. It may take a few moments for the queue to catch up to your question, so please don’t leave if you don’t see your question right away.

Akarsh_Valsan: Why does sun and stars twinkle while Moon don’t twinkle?

David: Basically because stars are pinpoints of light, so the scattering by atmospheric turbulence makes for light movement. An object like the moon or the planets is more spread out, so there are more light points coming through.

Akarsh_Valsan: Which is the nearest star to the moon?

David: The sun is the nearest star. :)

Akarsh_Valsan: Why is Sun classified as G2 Star?

David: G2 because of a historical mistake in spectral classification. They thought hot-cold stars went from A-down, and they got the alphabet mixed up.

Akarsh_Valsan: Can you reveal the reveal the interior of the Sun?

David: Yes, we have technique called helioseismology that looks at waves on the surface of the sun and used them to tell us about the solar interior.

Akarsh_Valsan: What is Doppler Effect?

David: The Doppler effect is due to the motion of the light-emitting objects in which objects moving towards us, light is shifted to the blue, objects moving away shifts to the red. We can use this to determine the speed of objects moving toward or away from us.

Abishek: will our sun turn to black hole some day?

David: The sun will not become a black hole. It's not massive enough to do so.

Nazban: what causes the 11 year solar cycle?

David: We know that it's due to magnetism which flows inside the sun, stretches out magnetic fields and make them stronger, but we're still trying to understand the details.

Alex: What can you tell us about Nasa's prediction of high solar activity in 2012, will it be powerful to the point of disruption electronic devices? To what extent?

David: That was my prediction, and it was wrong. :) I recognize that I made a mistake and have been predicting a small sunspot cycle for two years now that should peak in 2013.

Nazban: what determines the frequency of solar activity?

David: The sunspot cycle and solar magnetism. More sunspots = more activity such as flares, coronal mass ejections, and prominence eruptions.

kyle90: I'm wondering if there's been much thought on trying to probe the interior of the sun more directly, like by stationing a spacecraft on the opposite side of the sun from the earth and then sending a powerful radio pulse through it? Or perhaps dropping a large seismic charge into the solar atmosphere?

David: You can't send radio waves through it, but we have thought of positioning spacecraft on the far side of the sun so we can monitor the surface of the sun. That vantage point also allows for better helioseismology for probing the solar interior.

Koth: Our existence is so miniscule (time wise and size wise) in the grand cosmos view. We got to be very ignorant of the lot of phenomenon out there. What if there is a solar phenomenon that is waiting to happen that will catch us all by surprise one day and we are pushed back like a thousand years. Is that even a possibility or is it just pure stuff for science fiction. For example, I have heard how Sun flares or sun storms (?) can have devastating effects on magnetic fields. What happens if some unknown 'natural' disaster occurs and all the digital storage on earth gets wiped out? The data in universities, NASA, big tech corporations, personal computers…. everything gets irretrievably damaged? Any comments? Are we prepared at any level for something like that?

David: The sun has been "doing its thing" for 4.5 billion years. Humans have been here for three million of that, and we're still going strong. I don't think the sun has any nasty surprises for us!

ZacharyTroxell: How do you feel about the 2012 solar storm? Will it greatly affect us?

David: Our current predictions are that the next sunspot cycle peaks in 2013 and will be the smallest in about 100 years. While we DO expect flares and other forms of solar activity, we don't expect any worse than in recent cycles, If anything, it should be milder.

(Moderator Jason): We're working to answer your great questions. Keep them coming! To submit your own questions, 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.

Jonah: What makes the out layers of the sun so unstable as to eject flares and cause the coronal loops (from above pictures)?

David: It's all magnetism. The magnetic fields are produced inside the sun by the motions of ionized gases. Those magnetic fields rise thru the surface and can become twisted which results in explosions like flares and coronal mass ejections.

Greg_Putnam: Are the old photos from Skylab still used in research today?

David: I have that photo on my wall. :) But data today is so much better that we rarely go back an dlook at Skylab except for historical studies.

JeffT: What effect do the massive magnetic forces generated by the sun have on Earth?

David: Many effects. When a coronal mass ejection (CME) strikes Earth, it shakes the Earth's magnetic field and can produces surges of current in power lines and pipelines. This can cause power outages and pipeline corrosion. The magnetic disturbances also produce the northern/southern lights.

scaron: ive read that the different latitudes of the sun rotate in different times - do a solar "day" (weird concept)! would be different on the equator that at the poles - why is this? after 4B years why wouldn't it all be rotating together?

David: Since the sun is a big ball of gas, it doesn't rotate like a solid object. At the equator, the gases rotate once in about 24 days, near poles about once every 35 days. This is produced by the effects of the sun's rotation on convective (boiling) motions within the sun.

ZacharyTroxell: What is the sun composed of?

David: Mostly hydrogen, a little helium, and trace amounts of carbon, oxygen, nitrogen, etc.

jimmy: How is it not you think the sunspot cycle is going to be the SMALLEST when we've been told even on nasa's website that it was the STRONGEST in 100's of years?

David: I'm not sure which site says it will be the strongest in 100 years. Certainly not mine. :) One indication of the strength of a solar cycle is how strong the sun's magnetic fields were late in the previous solar cycle. Those fields were half as strong as they were before the previous three cycles, indicating a cycle about half as strong as those. Furthermore, following the rise in the number of sunspots since minimum in late 2008 clearly shows the beginning of a small cycle.

JeffT: What is your favorite attribute or statistic about the sun? Something you personally think is just awe-inspiring.

David: I just figured out that the sun burns up the mass equivalent of about one Earth every million years. E=Mc2 works great because "c" is so big!

fhavas: What happens to a filament of magnetism if it destabilized? (I.E. the current filament we are watching)

David: The magnetic fields in filaments, which are cool streamers of gas in the sun's outer atmosphere, are carried off the sun and thru the solar system when the filaments erupt. These mag fields are part of those that strike the Earth and can cause power outages and the northern/southern lights.

MCBBEuph: What are solar winds and what causes them?

David: This is still one of the biggest questions for solar physics. We know it's related to magnetism and the sun's hot corona (its outer atmosphere). The corona is so hot that the sun's gravity can't hold onto it. The question is why is the corona so hot? And there we think magnetism is the key.

sunchild: what type of materials will the spacecrafts be made out of that will travel to the sun in 2015?

David: I'm not sure of the material, but there's a heat shield shaped like a dunce cap that's aimed at the sun -- so the sunlight that hits it hits at a "grazing angle" and doesn't heat it up so much.

NASAFanBoy: Does the sun have magnetic poles, like North and South, like here on Earth?

David: Yes, it does. And like the Earth, those magnetic poles flip but much more regularly for the sun -- every 11 years, instead of every 100,000 years or so.

Rick_H: Which future solar space missions are you most interested in and why?

David: Solar Probe because it promises to tell us about the origin of coronal heating and the source of the solar wind.

kyle: I've heard that spectral lines for water vapour have been detected in sunspots. Are there any estimates as to how much water there is on the sun?

David: Water is only found in the very coolest places, or the centers of sunspots. It doesn't last long. The actual amount of water is probably extremely small.

Koth: Not a real Science question..but why not? :-)In so many ancient cultures world wide, Sun has always been in the forefront when it comes to 'making a god out of it'. Why do you think the moon did not 'enjoy' that status. It was also a heavenly body that lived in the sky for the unscientific ancient mind. Did the ancient people see something in the sun that so many cultures so far apart independently came up with the Sun God.

David: The sun's much more important for life, providing heat and light that far surpasses what the moon does. :)

Nazban: what is the density of the sun?

David: The density of the gas at the surface is almost a vacuum by our standards, much less dense than the air we breathe. But, the crushing weight of the mass of the sun makes the density in the core about 10x that of gold or lead.

Jonah: Is the entire mass of the sun ignited? The 'flames' that we see on the surface are obvious, but is that what it would be like if you could bore straight to the center?

David: Those aren't flames we see on the surface -- those are magnetic structures. The only place where any real burning happens is in the core -- the inner 10% or so. It's there that hydrogen "burns" to form helium and produce the light that ultimately escapes at the surface.

Mike_Tawil: If the peak of our current cycle is likely to be relatively small, can we look ahead to the next few cycles & anticipate whether any are likely to be seriously disruptive to human activity?

David: The sun appears to go thru cycles of cycles with big cycles following small cycles about every 100 years. It looks like the next cycle and perhaps one or two following that are apt to be small cycles. Small cycles are less threatening than big cycles. Furthermore, we're learning how to deal with the effects of this "space weather."

Greg_Putnam: Does the solar wind slow down as it moves out into the solar system?

David: It does slow down, but the solar wind isn't a steady flow. It changes in speed due to magnetic structures on the sun and consists of fast and slow streams.

Jet: Why does the magnetic poles flip, and what forces cause this to happen?

David: This is part of what we call the "solar dynamo." It's a rather complicated "dance" between motions below the surface of the sun and magnetic fields.

Nazban: You said every 11 years the poles flip, is this related to the solar cycle?

David: Yes, indeed. Of course, the cycles aren't all exactly 11 years long -- they typically range from 10-12.

drew: What is one of the top questions heliologists are working on, and what impact might the answer have on your field or on us non-scientists?

David: One of the key questions is the nature of the sun's meridional flow (a conveyor belt-like flow) that carries magnetic fields to the poles and the surface layers, but must return back to the equator somewhere deep inside the sun. We'd like to know where this happens.

scaron: You said the sun could not create a black hole - not enough mass - but will it create a nova or supernova at the end of its life?

David: Certainly not enough mass for a supernova, and some types of nova involve companion stars, which the sun doesn't have. Stellar evolution theory says the sun will become a red giant after it burns the hydrogen in its core and the core will collapse to become a white dwarf.

ludmila: What most fascinates you in the sun, what property?

David: Its magnetic field. Without magnetism, the sun -- while important -- would be rather boring. :)

muckraker: What has been the most surprising thing you have learned from the recent data collected by the Solar Dynamics Observatory? The images have been phenomenal!

David: I'm amazed at how much magnetic activity is going on down to the limit of resolution even with this high-resolution mission. I'm also amazed at how much data it makes! It's like drinking from a fire hose.

Akarsh_Valsan: Does our Sun have any companion?

David: No, we'd know if it did by the motions of the planets, and our spacecraft trajectories to those planets.

(Moderator Jason): We're working to answer your great questions. 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.

Nazban: What is the Habitable zone of a solar system?

David: The habitable zone is the region where a planet could exist with liquid water for a long enough time for life to evolve. It extends from about the orbit of Venus to about the orbit of Mars for the

ZacharyTroxell: What is the sun's current biggest mystery? Is there anything big that we are haven't been able to explain?

David: There are three big mysteries, and all are related to magnetic fields: 1) how is the sunspot cycle made; 2) how are flares and other eruptions triggered; 3) how the sun's corona is heated to form the solar wind.

jaznique: is the sun relatively similar to Jupiter?

David: Jupiter is far too small to be a sun-like object, but it's similar in composition and in the fact that it's largely a ball of gas.

duclicsic: This is not strictly sun related, but more stars in general. I wonder if we know, or can estimate the percentage of baryonic matter in the universe that has at some point been part of the composition of a star?

David: We probably could, and we certainly know that all of the carbon, oxygen, and nitrogen, etc. that makes up our bodies were once part of a star. That's the only place the Universe makes those elements.

Escale: Does the sun make any noise?

David: Great question! Helioseismology is based on waves that are acoustic or sound waves. The boiling motions near the sun's surface can become supersonic and create shockwaves that are quite noisy. However, this noise remains trapped inside the sun and is at such low frequencies that we'd have a hard time hearing it.

LRFalk01: With all this talk about the Sun's magnetic fields, and the affects these fields can have even here on Earth, what keeps these magnetic fields from pulling in ferrous metals? Am I confusing these magnetic fields with actual magnets? If so, how are they different?

David: These are the same magnetic fields that attract ferrous metals, but more importantly, they control the movement of ionized gases. This is why we see all those fantastic structures in SDO images. ( Of course, the strength of the field falls off quickly, so here on Earth, it's the Earth's magnetic field that dominates.

rd_holmes: Under what circumstances might Jupiter ignite?

David: Jupiter needs to be about 100x more massive than it is to ignite hydrogen.

Bob: David Bob here from SolarCycle I would like to ask how much we know about the development cycle of a Sunspot. We at have noticed that early in the development of a Sunspot the Magnet Signature is low but the energy in the 304A spectrum (UV) is comparatively high. As the Sunspot matures the magnetism increases leaving a more visible signature but the 304A energy drops off. Have you noticed this ? Is there an explanation ?

David: I haven't noticed this specifically, but certainly we see magnetic fields before we see the sunspots. Those magnetic fields would show up in 304, and it may be that as the sunspots become more developed, the heating of the strong fields out of sunspots may diminish.

JeffT: Not a question! I wanted to thank Dr. Hathaway and the moderators for making this happen. This has definitely made my day! Thank you.

David: You're very welcome! Thanks for being here and asking great questions.

fornitta: How many years is left before the sun dies?

David: About 4.5 billion years, give or take a billion. :)

Escale: If we had a spaceship strong enough to get close to the sun, would it be able to go through it? That is, is the sun not-solid?

David: No, while the sun isn't solid, it's dense enough at the core and hot enough that virtually nothing could survive a passage through it.

Escale: Does the sun moves inside the Galaxy? I know that galaxies are moving (big bang theory) but does the Sun rotates or moves in any way?

David: Yes, it does. The sun moves within the Milky Way galaxy and takes about 200 million years to orbit once around the galaxy center.

TravisTX: Why don't we put nuclear waste on a rocket and send it to the sun for safe disposal?

David: The cost would be prohibitive!

Mike_Tawil: I see that Voyager 1 has now passed 16 light hours of travel from Earth. Can it still detect the sun's presence at that distance?

David: Yes, it can. We're still gathering data from Voyager 1 and 2, and they relay information about the solar wind and its interaction with the local interstellar medium.

magneticdynamo: If I had my own space shuttle and flew it to the sun, how close could I get before I blew up?

David: First off, our space shuttle doesn't go there. :) We are sending Solar Probe close to the sun, but the closest it can get is about three to four million miles.

MonkeyLover: Speaking of solar cycles, do you feel 2012 will be as devastating as some are predicting it to be?

David: No, it won't.

(Moderator Jason): Great questions everybody. We're trying to get to all of them, so please be patient. Thanks.

33King: What kind of danger does Sunspot 1112 really pose to us?

David: Sunspots like 1112 can produce flares and coronal mass ejections that can impact satellites in orbit (possibly disabling components) and even produce power outages here on Earth. Luckily, we have space weather monitors between us and the sun that can give us a "heads-up" if something particularly destructive is heading our way. This is a good link about 1112:

Alex: Is there any validity to the galactic alignment claims and, if so, is there any way to predict its effects?

David: This comes up with discussions about Dec. 21, 2012. It turns out that the sun appears to pass in front of the galactic center every year at about that time.

Nazban: What is the main aim of SDO?

David: To understand the sources of solar activity that can impact the space environment and influence our lives on Earth. This is my paraphrasing of the aim, check out the Web site for the official answer:

Nazban: Thank you so much for answering all our questions!!

David: My pleasure!

Greg_Putnam: How much stronger is the sun's magnetic field compared to the earth's?

David: The magnetic field in the center of sunspots is nearly 10,000x stronger than the Earth's polar field.

sunchild: is there strong evidence to suggest that the weather on the sun is directly related to large storms here on earth, i.e.: hurricanes?

David: Not directly to storms like hurricanes, but there does appear to be a link, albeit weak, to climate.

Abishek: sir solar winds are fishy can they propel my spacecraft?

David: Sunlight from the sun is far better at driving solar sails than the solar wind itself.

dexer: I've arrived a little late so forgive me if the question has been answered before. I've read a bit about how the solar magnetic field is spiral shaped which is related to the reversing of the magnetic field and its 11 year cycle. (First off, is this correct? Anything interesting to add to this?) While I find that exceedingly interesting, what really grabbed my attention is when the heliosphere hits the heliopause. Can you tell us a bit about the heliopause?

David: Yes, because of the sun's rotation, the magnetic field in the solar wind is in the shape of a spiral coming out of the sun and spreading out through the solar system. This field get compacted when the solar wind hits the heliopause (interacts with the local interstellar medium). This compacted field can have interesting effects on ionized particles entering or leaving the solar system.

MonkeyLover: When the sun ascends to Red Giant status how long will it take, from beginning to end, for the corona to fully engulf Earth?

David: I don't know exactly, but I think it's on the order of millions of years.

Akarsh_Valsan: Have sun collided with any heavenly body?

David: Yes, we've seen numerous comets or numerous parts of a comet, impact the sun using the coronagraph on the SOHO mission. This is the link:

(Moderator Jason): We've got time for one more question...

Koth: You said…The sun rotates around the center of the galaxy and moves too…. Are there chances that this could change the Goldilocks range for planets in our solar system?

David: If the sun passed through a particularly dense region or through a cluster of particularly bright stars, then it might.

Escale: Thanks David for this great experience!!

David: It's always my pleasure to talk with interested people about the sun, and all the incredible things it does. It's good to see people sharing in the quest for knowledge. :)

Mike_Tawil: Thanks for your time :-)

David: My pleasure! And thank you for yours.

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