LIVE FROM THE SUN - "Our Sun In Close Up"

ON-AIR FAQ "Our Sun In Close Up"

ASTRONOMY   CME (CORONAL MASS EJECTIONS)    COMPOSITION OF THE SUN   CORONA
DISTANCE TO THE SUN   ELECTROMAGNET SPECTRUM    FLARES   FUSION   HELIOSEISMOLOGY
KITT PEAK   LIFE CYCLE OF THE STARS    MAGNETISM    NASA   RADIATION    ROCKETS
SATELLITES   SIZE OF THE SUN   SOHO SPACECRAFT   SOLAR MAXIMUM    SOLAR PHYSICIST
SPACE WEATHER   STARS   SUN    SUNSPOTS   TELESCOPES (GROUND BASED)
TEMPERATURE OF THE SUN   TRACE SPACECRAFT

ASTRONOMY (CAREERS IN)

QUESTION:
I have been interested in astronomy and astrophysics since I could read. I'm in advanced courses in high school and I wanted to know what schools have good programs for astronomy and astrophysics, and once I have graduated from college what kind of jobs are available--thanx!

ANSWER:
There are many good schools for astronomy, but if you want to be a professional astronomer, I STRONGLY recommend that you get an undergraduate degree in physics. This is the best preparation for graduate school in Astronomy. After college, you can either go on to graduate school, or you can work at an observatory as a telescope operator, programmer, electronic technician, optician, or any type of engineer.

QUESTION:
Hello me again! If I were to go to get a graduate degree what kinds of jobs are available?

ANSWER:
If you get a masters you will be able to work as a research assistant and perform research. If you go all the way to a Ph.D, then you will be a professional astronomer. Possible working places are universities, observatories, and NASA.

QUESTION:
I have been interested in astronomy and astrophysics since I could read. I'm in advanced courses in high school and I wanted to know what schools have good programs for astronomy and astrophysics, and once I have graduated from college what kind of jobs are available--thanx!

ANSWER:
Virtually every college and university offers elementary astronomy courses, and many of them offer upper level and graduate programs in astronomy. Check www.aas.org for the American Astronomical Society's resources. All sorts of skills are useful in astronomical research, and there are jobs available in research, engineering, computer sciences, and the list goes on and on. The important thing is to have a passion for exploring the universe, as well as the basic tools for the discovery process--physics, math, and curiosity!!! ;-)

QUESTION:
I wanted to know how many years it takes of college to become an astronomer like Detrick who operated the telescope and spectragraph.

ANSWER:
I'm not sure, but I think with a regular bachelor's degree in physics--4years--and some good summer experience at an observatory, you'd have a good background and could start doing interesting work--and having a good time to boot!!!

QUESTION:
Why is the corona hotter than the surface of the Sun?

ANSWER:
This is one of the outstanding mysteries of solar physics. We think that energy is transported by waves in the gas that forms the corona (like sound waves or waves in the magnetic field). However, we are still unable to correctly calculate the temperature of the corona from these theories.

QUESTION:
Why is the corona hotter than the surface of the Sun?

ANSWER:
The answer is: nobody knows! Your question is one of three questions SOHO was designed to help us answer. There are many theories as to how the corona is heated. These theories try to heat the corona by taking energy from lower down in the solar atmosphere and depositing it in the corona by various mechanisms. SOHO is designed to, look for evidence of these mechanisms. There is some evidence supporting some of these mechanisms, but it is by no means conclusive. So, still, nobody knows for sure!

QUESTION:
Why is the corona hotter than the surface of the Sun?

ANSWER:
We don't really know, This is one of the big mysteries we are trying to solve. We think it has something to do with the Sun's magnetic fields. Somehow they are conveying energy up into the corona. With SOHO we have learned that the Sun's magnetic field is renewing itself on a small scale all the time. Where does it go? We think some of the magnetic field may be transformed into heat in the corona. We are not quite sure how this happens, though.

CME (CORONAL MASS EJECTION)

QUESTION:
How large are CME's? Connor, Ms. Hammonds

ANSWER:
When they arrive at the Earth, they are about 30 million miles across. They have a mass of about a few 10 million million kilograms, or about a billion tons. Jack.

COMPOSITION OF THE SUN

QUESTION:
What is the Sun make of?

ANSWER:
I think I got this question by mistake--but I can still answer it! As THEY MIGHT BE GIANTS sang in the program intro "The Sun is a ball of incandescent gas"--mostly hydrogen and helium. You can find much more information by using the URLpost section of the website. Thanks for your question! Geoff Haines-Stiles Producer/director, LIVE FROM THE SUN

QUESTION:
What is the inside of the Sun called?

ANSWER:
We have named the parts of the inside of the Sun: the core, the radiative envelope, and the convection zone. The core is the innermost 30% of the Sun by radius, and is where the nuclear reactions that power the Sun occur. The radiative envelope is the middle 30% and here the energy quietly flows through the solar gas by radiation. The convection zone is the outer 30%, and here the gas is unstable and is moving in a complicated fashion called convection, which is like water boiling in a pan.

QUESTION:
Would you explain what kind of atmosphere the Sun has?

ANSWER:
This is a very good question. The Sun is not like Earth with a hard surface and an atmosphere above it. It is, instead, a ball of hydrogen and helium. The whole Sun is made up of gasses but they are much more dense than the gasses in our atmosphere. There are several distinct layers in the Sun. The center of the Sun, or Core, has a pressure three billion times the pressure of the atmosphere at the surface of the Earth. The Radiative Zone is a seething mass of energy where energy from the core is passed to the surface of the Sun The Convective Zone is the source of the redistribution of energy. Like bubbles in a pot of boiling water, blobs of hot gas move up and down in this part of the Sun. The Photosphere is a very thin layer near the outer part of the Sun. All of the photons, or light, that we see come from the photosphere. The Chromosphere is another thin layer above the photosphere. Here there are other gasses besides Helium and Hydrogen. The Corona is the enormous halo around the Sun reaching out millions of kilometers. So you see, the Sun doesn't really have a hard surface with an atmosphere like Earth. Instead, it just gets thicker and thicker as you go down through the layers of the Sun. Even at the center of the Sun, there is no hard core of rock but just more gas and more gas that gets denser and denser.

QUESTION:
What is the inside of the Sun called? ANSWER:
The center is called the 'core', where hydrogen is 'fused' into helio; above that is the 'radiative zone' where energy is transported by radiation, then there is a 'convection zone' where energy bubbles up toward the surface, where the energy shines away into space.

DISTANCE TO THE SUN

QUESTION:
How close have we got to the Sun?

ANSWER:
I think that Mercury is as close as we have gotten so far.

QUESTION:
Do you think we will ever reach the Sun? Lindy, Ms.Hammond's fifth grade class Rancho Santa Fe School

ANSWER:
Hmmmm.... I'm not sure what you mean by that. If you mean, "Will we be able to launch a spacecraft that will land on (or hit) the Sun?" Then yes, of course we will. It's actually easier to make a lump of material hit the Sun than it is to throw the same lump of material out to the outer planets. As far as landing *people* on the Sun: there's no solid surface to it, so it doesn't make much sense to think about landing on the Sun. One day, I suppose people might fly down inside the Sun, but not for at least several decades (that is, not in the foreseeable future!)

QUESTION:
How close can you get to the Sun because of the extreme heat.

ANSWER:
The best answer is: we don't know! The Sun is pretty hot, but not all *that* hot--it's only about 6,000 degrees Kelvin, which isn't that much hotter than the flame from an oxyacetylene torch. We (NASA) plan to send a probe to within 1,600,000 miles of the Sun in the next few years. That's pretty close--only about twice the Sun's diameter. But without special protection, you wouldn't want to get very close at all. 93,000,000 miles is how far you are now, and you wouldn't want to get much closer without a spaceship anyway!

QUESTION:
If you could get to the Sun in one minute, how fast would you have to go?

ANSWER:
Hello! It takes eight minutes for light to get from the Sun to Earth. And the speed of light is the fastest we can go! For us to get to the Sun in one minute, we'd have to go eight times faster than light. Faster-than-light travel is a common subject of science fiction books! Barbara Thompson

QUESTION:
How do you measure the distance between Earth and the Sun?

ANSWER:
You can measure the distance from the Sun to Earth at eclipses. At eclipses the moon covers the Sun. Therefore they both have the same angular width. If you know the radius of the moon and the Sun then you just draw a triangle.

QUESTION:
How can machines go near the Sun without being burned? Suzi in Ms. Hammonds' class, Rancho Santa Fe, CA

ANSWER:
Machines can go near the Sun without being burned, by being carefully insulated from the Sun's rays. A large, mirrored shield placed in front of the machine would protect it from the hot rays. SOHO, the Solar and Heliospheric Observatory, is closer than we are to the Sun--but only about 1% closer. That's not all *that* much closer, so we didn't have to worry that much when we designed it. But the Solar Probe, which you can find by searching for "Solar Probe" at the AltaVista web index site, will go very close to the Sun indeed, and it has a very carefully designed Sun shield. Dr. Craig DeForest

QUESTION:
How long would it take to get to the Sun in a F-14 Tomcat. Victoria

ANSWER:
An F-14 could never get to the Sun by itself, as it relies on burning fuel in an oxygen atmosphere. As there is no oxygen atmosphere between the Earth and the Sun it could never actually travel there! But let's say you could travel at the same speed as an F-14. That's about Mach 5, or about one mile per second. It's about 93 million miles to the Sun, so that is about 93 million seconds, or about 3 years. Jack

ELECTROMAGNETIC SPECTRUM

QUESTION:
How many different colors is the Sun?

ANSWER:
The main colors the Sun gives off are in the yellow part of the spectrum, but it gives off at least some light in almost all "colors", even the ones we can't see. Astronomers study radio waves, infrared light, visible, ultraviolet and even X-rays and gamma rays from the Sun and other stars.

QUESTION:
How come flares return to the Sun and don't float into space?

ANSWER:
Flares occur in loops low in the Sun's corona. Material in the loops is heated and energized. Most of it is held in the low loops by the magnetic field. Sometimes, though, particles do escape along magnetic field lines that open into space. There are other things which happen on the Sun called Coronal Mass Ejections in which giant bubbles of gas explode out from the Sun, so some things do escape.

QUESTION:
How come flares return to the Sun and don't float into space?

ANSWER:
Well, actually, flares don't return to the Sun! A flare is a sudden brightening of the glow coming from material that's already present over the surface of the Sun. The flare happens because the material is suddenly heated. Flares disappear because, once the heating disappears, the material cools down again.

QUESTION:
When the Sun shoots solar flares every eleven years could it hurt the Earth? Max

ANSWER:
We think solar flares have been happening for as long as the Sun has been around. They haven't done any serious damage to things on the Earth's surface. So we don't expect solar flares to actually hurt the Earth. We do have to worry about people in space, and we also have to protect some of our technology (like power lines and satellites) from the effects of coronal mass ejections, which increase and decrease with the solar cycle as flares do.

QUESTION:
Why does it take so long (although geologically I suppose it isn't that long)--170,000 years for energy to get from the core to the next region in the Sun? I thought fusion of Hydrogen to Helium would happen quickly. Why does the pure energy take so long to travel?

ANSWER:
The Sun is very dense. Think of it like a subway car. If you want to go from one end to the other when no one is in it you can go very quickly. If there are lots of people in the car, it may take you hours to get from one end to the other. Light has the same problem as the crowded car. It keeps bumping into electrons and protons so it takes a long time to get out.

QUESTION:
When did you find out that the Sun had nuclear energy? And how?

ANSWER:
This was a question that had a lot of people stumped at the turn of the century. People thought that there was something like coal burning, but that didn't work since that would mean that the Earth was older than the Sun, which is a bit strange. Then they thought the energy generated by a gas collapsing under it's own gravity could power the Sun, but this idea ran into the same problem as the coal one. Then Einstein found the equation E=mc^2 just after the turn of the century, which converts mass into energy. This process gives enough energy to power the Sun. Jack

HELIOSEISMOLOGY (Sun sounds)

QUESTION:
How do you know what's inside the Sun? Suzi Ms. Hammonds' Class, Rancho Santa FE, CA

ANSWER:
Hi Suzi--We can calculate what the inside of the Sun is like using physics, mathematics, and computers. Until about 40 years ago, that was all we could do. Then we discovered that the Sun is ringing like a bell--it's a huge musical instrument. We can "listen" to this sound (actually by watching it), and then use the information in that sound to deduce what the inside of the Sun is like.

QUESTION:
Why do you "catscan" the Sun?

ANSWER:
Hmm. I don't know exactly what you mean by catscan (did they use that phrase on the TV show :-)?) Anyway, One way we can see into the Sun is with heliosiesmology. We can study the vibrations of the Sun to figure out what is going on inside. Another way we would like to study the Sun is to put more that one spacecraft in Earth's orbit, but out away from the Earth. The spacecraft could give us a stereo view of the Sun, and in fact the proposed project is called STEREO. http://stprobes.gsfc.nasa.gov/stereo.htm STEREO would use some of the same techniques used in a catscan to understand the Sun.

QUESTION:
How complicated is your job and can you get distracted real easily? Willard Middle School

ANSWER:
The job is fairly complicated, you have to do things in the right order. It's easy to get distracted at sunrise!

QUESTION:
We were listening to Dietrick explain how the vacuum tower telescope works, but we were confused about the role of the celeostat. Does it focus the Sun or monitor weather? Taylor Road Middle School

ANSWER:
The Celeostat is a type of telescope we use to observe the Sun, not the weather. We also use a telescope called a heliostat. The difference is in the arrangement of the mirrors, which are raised on a mast for the celeostat but not for the heliostat. The image of the Sun rotates during the day on a heliostat, but not for a celeostat.

LIFE CYCLE OF THE SUN

QUESTION:
Will the Sun ever shrink?

ANSWER:
Yes the Sun will shrink when it runs out of hydrogen and helium. Nuclear reactions will cease, so the Sun will start to cool and collapse. An example would be to fill a balloon with warm air. Then cool the balloon and watch it get smaller. This is the same thing that the Sun will do.

QUESTION:
When the Sun becomes a red giant will the Earth be consumed?

ANSWER:
I think the Sun is supposed to expand past the Earth's orbit when it becomes a Red giant.

QUESTION:
Is it true that the Sun will expand over the four inner planets in a couple million years? Victoria

ANSWER:
Not so fast!! ;-) Everything is 'under control' for the next 4 or 5 BILLION years--basically as long as the Sun has already been around--and then yes it will expand and its outer atmosphere will envelope the inner planets... ;-(

QUESTION:
How does the magnetic field of the Sun change during its cycle?

ANSWER:
The Sun's magnetic field goes from being relatively simple (like that of a bar magnet) at solar minimum to being very complex at solar maximum. It takes it about 11 years to go from solar max to solar min. You may have heard of this. It is also called the sunspot cycle because the number of sunspots increases as the Sun's magnetic field gets more complex.

QUESTION:
What do you know about NASA?

ANSWER:
I know that it has a URL: http://www.nasa.gov and that you can see really cool stuff about the Sun if you look at http://sohowww.nascom.nasa.gov

QUESTION:
Infrared radiation is caused by low energy photons that are observed by what matter they come in contact with, causing heat, but if that's true why does living matter produce infrared radiation? Willard M.S

ANSWER:
Infrared radiation >is< the low energy photons. Anything which is at a temperature greater than absolute zero radiates photons. The hotter the thing is the higher energy photons it produces. If you heat up a burner on a stove it will start producing red photons. Hot stars can produce blue photons and even ultraviolet and X-rays photons. Living things, like people are not very warm, but we are warm enough to produce low energy photons.

QUESTION:
When was the first rocket sent in space???

ANSWER
This is from the "Windows to the Universe" site: The earliest evidence of rockets is from 1045 A.D. by the Chinese who used them in their military tactics. The destructiveness and range of rockets soon made them popular in other Asian countries and throughout Europe. By World War II, technology had developed liquid propulsion systems which were more efficient than solid fuels like gunpowder, and revolutionized rocketry. The 1942 launch of a German rocket which hit a target 120 miles away marked the beginning of the space age. Since then, continuing research by the U.S. and Soviet space programs has resulted in more and more powerful rockets. Today, rockets make space travel possible throughout the entire solar system. The "windows to the universe" site is a great place to visit! Try: http://www.windows.umich.edu/ Best wishes, Barbara Thompson

QUESTION:
How many satellites are in space right now ?

ANSWER:
The United States Space Command keeps track of things launched into space. Its web site http://www.spacecom.af.mil/usspace/boxscore.htm says that there are now (on 16 March 1999) 2569 satellites, 89 space probes, and 6145 pieces of debris in space, for a total of 8803 things. A "space probe" is something that was sent between the planets, beyond the influence of the Earth. A "satellite" is something that was sent to work in an orbit around the Earth. "Space debris" is anything that was sent into an orbit around the Earth but that does not do anything useful there, such as bits and pieces of the rockets that brought the satellites and space probes into space.

QUESTION:
Will Y2K affect any satellites? And if so, which ones?

ANSWER:
NASA is being very careful to try to ensure that all spacecraft and ground systems are ready for Y2K. We are working hard on it and expect everything will be OK.

QUESTION:
Wouldn't the satellites float off somewhere if they are taking pictures farther than our atmosphere?

ANSWER:
Satellites are held in place by gravity, which extends throughout all space. They are held in place by the same force that holds the planets in their courses and keeps the Moon near the Earth. (remember not to think that satellites are somehow glued down -- they're in constant motion, moving around and around whatever they're orbiting!)

QUESTION:
How many satellites go around Earth? Jamie

ANSWER:
It is my understanding that there are thousands. There are all the US commercial and science ones, there are all the non-US commercial and science ones, there are all the US military ones and all the non-US military ones.

QUESTION:
In the future, would it ever be possible to build a spacecraft that could go through the Sun to increase knowledge of the Sun? from Jessica at Taylor Road Middle School

ANSWER:
It may be possible to build something to withstand the heat, but there would be the same problem as light getting out. It would keep bumping into protons and electrons. It would be like trying to push through a cement wall. Even though the Sun is a gas, it gets very dense.

QUESTION:
Will Earth ever fall out of orbit? Jamie, Ms.Hammonds class, Rancho Santa Fe School, CA

ANSWER:
No. It would take a large amount of energy to stop the Earth so it would fall out of orbit. It can't happen naturally.

SIZE OF THE SUN

QUESTION:
How big was the Sun when the Earth was first formed? from Jared at Taylor Road Middle School

ANSWER:
It was about the same size as it is now. In several billion years, it will expand enormously and swallow up Earth.

QUESTION:
How big is the Sun?

ANSWER:
The Sun is about 865,000 miles in diameter. That may sound pretty huge -- the whole Earth is only about 30,000 miles around -- but professional truck drivers might drive that far (around and around our highway system) in only a few years!

QUESTION:
How many moons could fit in the Sun?

ANSWER:
You can fit 216 times as many moons into the Sun as you can fit Earths. The radius of the Sun is 696,000 km, and the radius of Earth is 6400 km. Assume they are perfect spheres. The moon has 1/6 the radius of Earth. So now all you need to do is the math.....!

QUESTION:
How big is the Sun? Is there more than one Sun? What is the temperature of the Sun? How close can we get to the Sun without burning? How was the Sun created? What is the color of the Sun?

ANSWER:
Hi, there. I'm not an astronomer, but the writer of the program. I'll do my best, and pass you on to NASA or Kitt Peak if I can't think of the answer. The Sun has about 109 times the diameter of Earth, and 1 MILLION Earths would fit inside. There is more than 1 Sun--all the stars you can see in the night sky are "suns"--though we don't know how many planets orbit them! The Sun's core is about 15,600,000 degrees--the outer layers, 5,700 degrees and the corona 2-3 million degrees! And I think you'll find answers to your other question--about the Sun's colors--in the Q&A database online. Thanks for your QUESTIONS! Hope you enjoy LIVE FROM THE SUN, Geoff Haines-Stiles

QUESTION:
What would happen to the Earth if the Sun were twice as big? Willard MS

ANSWER:
It would be a lot hotter here. Life probably wouldn't exist on the Earth.

QUESTION:
What would happen if the Earth was the same size as the Sun? Willard MS

ANSWER:
If Earth was the same size as the Sun, our gravity would be MUCH stronger. This would affect many things--the shape of life, any buildings, etc. HOWEVER, just about any astronomical body that is the same size as the Sun is a star itself because once something is that big, it can contain the nuclear reactions inside without blowing apart. Jupiter, the largest planet in our solar system, is almost big enough to be a star.

SOHO SPACECRAFT

QUESTION:
How long did it take SOHO and the other spacecrafts to travel to the orbit that they are in now?

ANSWER:
It took SOHO about a month to get very close to orbit so we were able to start taking data after about a month. It took about 3 months for actual orbit insertion. Most satellites are in Earth orbit, so it only takes about an hour. For geosynchronous orbit it takes about half a day.

QUESTION:
Are we prepared for the solar maximum? If so, how?

ANSWER:
Hello--there are two answers to the "solar maximum" question. Are people prepared for solar maximum? Well, we had one about 9 years ago and we survived all right! Humanity has been enduring solar maxima (without noticing it!) all along. Are scientists prepared for solar maximum? Well, we want to have our observations prepared--we have a lot of spacecraft and observatories, so I hope that the upcoming solar maximum will be the most studied one ever! There are spacecraft and satellites which will depend on our ability to observe the Sun as it erupts, to warn them of impending danger. I hope we're ready! Barbara Thompson

SOLAR PHYSICIST (CAREERS IN)

QUESTION:
Explain how you get the plan to make new instruments to study the Sun?

ANSWER:
It's a long process. A scientist comes up with an idea to analyze the light from the Sun. Then she proposes for the money to build it. If she is successful, then it gets carefully designed by a team of scientists, engineers, and programmers. Finally it gets built and used for research.

QUESTION:
What would happen if the Earth was hit by a solar flare?

ANSWER:
It happens all the time. The Earth is often "hit" by solar flares. Many different things happen. The ionosphere gets excited and short wave radio communications get disturbed. Sometimes satellites get messed up. I suggest you look at the space environment center, NOAA web pages to get more information on this.

QUESTION:
What is protecting our astronauts from solar flares?

ANSWER:
To some extent they are protected by the Earth's magnetic field. So, it will be more dangerous when we go back to the Moon or when we go to Mars. To some extent their spacecraft protects them. It is not a good idea to go out of the spacecraft during a flare. Also, to some extent we have been lucky.

QUESTION:
Does the Sun's magnetic field affect compasses on Earth?

ANSWER:
Hello! The Sun's magnetic field does indeed affect compasses on Earth. It was one of humanity's first clues that there is a vast space environment out there. However, the process is a little complicated. The "Live from the Sun" broadcast mentioned the "solar wind." The solar wind is the expanded atmosphere of the Sun. It extends all the way to Earth. The solar wind has a great deal of magnetic field in it. When it reaches the Earth, it interacts with the Earth's magnetic field, and we can even measure it here on the ground! There are lots of observatories on Earth dedicated to measuring the fluctuations in the magnetic field. When a major solar magnetic storm hits Earth, the magnetic fields, measured by magnetometers, can go wild! We still find these observations very worthwhile. Best wishes, Barbara Thompson

QUESTION:
How do the solar winds affect Earth?

ANSWER:
The solar wind has many effects on the Earth. I'd suggest you look at the following web page: http://www.sec.noaa.gov/sec.html http://www.windows.umich.edu/

QUESTION:
What creates solar wind? Ben, Willard Middle School

ANSWER:
We are not really sure of the correct answer to that question. It is an important topic of current research. We think that magnetic energy somehow gets translated into kinetic energy in the corona. This heat supplies the energy that causes the solar wind.

QUESTION:
How do we measure the brightness of stars? How does the brightness correlate to the number of stars in the galaxy? This is so cool!!!

ANSWER:
We measure the brightness of stars with an instrument called a photometer. You can think of it as a fancy light meter for a camera. The more stars a galaxy has, the brighter it is, but a more important factor is how far away the galaxy is--the further away, the dimmer. The same holds true for stars. Dust between the star and us can also make it appear to be dimmer.

QUESTION:
How far away from the Earth can the Sun actually be seen in space? from Sean at Taylor Road Middle School

ANSWER:
The Sun can be seen in space for many light years, like any other star.

QUESTION:
How many stars are there like the Sun?

ANSWER:
The Sun is a very common type of star. I would guess that there are several billion stars like it in every galaxy, and there are billions of galaxies.

QUESTION:
How many stars do you think are in the Milky Way? Jamie

ANSWER:
The Milky Way (Our galaxy) contains about 10 billion stars.

QUESTION:
How many stars do you think are in the Milky Way?

ANSWER:
Roughly 10,000,000,000 +/- a bunch. But it's hard to count, new ones keep forming and older ones fade out or explode.

QUESTION:
What is the average size of a star? Dustin, Ms. Hammonds

ANSWER:
Stars have a large range of sizes. The largest are red supergiants, with a size (radius) about 100 times larger than the sun. The smallest are white dwarfs, which are smaller than the Earth, The Sun has a radius of 700,000 kilometers, the Earth has a radius of about 6300 Km

QUESTION:
How big is the largest star, that we know of?

ANSWER:
According to Sten Oldenwald of "Ask the Space Scientist", "The biggest star I know in physical size is the supergiant star Mu Cephi about 1800 light years distant, and believed to have a surface that extends past the orbit of Saturn if placed in our solar system. The bright star Betelgeuse in Orion is about 1000 times the radius of the Sun, with an outer surface that would be out past the orbit of Mars."

QUESTION:
How do we measure the brightness of stars? How does the brightness correlate to the number of stars in the galaxy?

ANSWER:
It's all relative! ;-) If we start with a standard star like the Sun, we can put A LOT of filters in front of a detector, until the light on the detector is the same as the light from a star without any filters, and then measure the transmission of the filters that were required to make the light on the detectors the same. Then we know how much fainter the star is than the Sun!!! Nuthin to it!!! The correlation between a single star and the number of stars in a galaxy is quite complex--that is to say it's a subject of active research!! ;-) But basically, stars are quite similar from galaxy to galaxy; young galaxies tend to have more bright stars, which go through their life cycle more rapidly than fainter stars; so older galaxies tend to have more faint stars. Check the LFSUN WWW site, which has LOTS of URL's for astronomical sites. g'luck

QUESTION:
Is there life on the Sun? Byran

ANSWER:
It is way too hot to support life as we know it. On most of the Sun it is too hot to keep molecules or even atoms together?

QUESTION:
Will life be destroyed if the Sun burns out?

ANSWER:
Let's say you switch off the Sun somehow. It takes 1 million years for the light from the center of the Sun to reach the surface of the Sun. That light then takes about 8 minutes for that last light from the Sun to reach us, because that's how long it takes light to get from the Sun to here. After that light goes, the Earth would be dark and start to get very cold. Very very cold. All photosynthesis would stop and so nothing would grow. If nothing grows, there is nothing to eat. Meanwhile everything is freezing, even the air itself. It would be very unlikely that any kind of life as we know it would survive, if the Sun switched itself off. Jack

QUESTION:
What would happen to the Earth without the Sun? Willard MS

ANSWER:
The Earth is kept in orbit by the Sun. If the Sun were completely taken away then the Earth would just wander off into space. If you switched off the Sun then the remaining light in the center of the Sun would eventually get to the outer surface (it takes about 1 million years). Then once that is gone the air would liquify and all life on Earth would die.

QUESTION:
What is the average size of sunspots?

ANSWER:
Sunspots range from as small as North America, to many times larger than the Earth itself. Sunspot *groupings*, clusters of many sunspots, can be simply enormous. Sometimes very large ones, dozens of times larger than the Earth, can be seen with the naked eye at sunrise and sunset. I remember seeing my first sunspots on a Boy Scout campout in 1979, at dawn. Dr. Craig DeForest

QUESTION:
I understand that you check for the change in sunspots every day. How do the sunspots change, and how could that information help us out?

ANSWER:
Sunspots are areas where the Sun's magnetic field is very strong. Watching changes in the numbers of sunspots over long periods of time can allow us to track changes in the solar cycle--the 11 year period over which the Sun's magnetic field becomes more and less active. Also, watching individual sunspot groups can give us an idea of how different active regions change. Larger more complex sunspot groups are more likely to have solar flares.

QUESTION:
If the sunspots are magnetic wouldn't they pull the satellites orbiting the Sun into the Sun? Or are the satellites too far away?

ANSWER:
You are correct--the satellites are too far away. Most of our satellites within a million miles of Earth, but the Sun is still 93 million miles away! The magnetic field measured by satellites are usually around a trillionth of the size of the Earth's magnetic field. Best wishes, Barbara Thompson

QUESTION:
If the sunspots are magnetic wouldn't they pull the satellites orbiting the Sun into the Sun? Or are the satellites too far away?

ANSWER:
Sunspots are magnetic, but the magnetic field is very weak compared to the gravitational forces that hold satellites in orbit. The magnetic field inside a sunspot is about 2,000 Gauss, or about 4,000 times stronger than the Earth's field (or about 40 times stronger than a refrigerator magnet's field), but we're pretty far from the sunspots. Sunspots mainly affect us because they are associated with "Active regions" above them, that can hurl large amounts of ionized (electrified) gas out into space. When the gas happens to hit the Earth (sometimes it's pointed our way), it can cause electrical effects here that confuse or paralyze satellites. But the satellites still continue orbiting--Sir Isaac Newton takes care of that--even if they aren't working properly.

QUESTION:
How many sunspots are visible at the current time?

ANSWER:
I think about 20 small ones and about 5-10 main ones. You can see for yourself by looking at the SOHO images for today. Go over to http://sohowww.nascom.nasa.gov and click on "Latest Images". Click on today's date under "SOHO Summary data" and then find an "MDI Intensitygram". That's a fancy name for a picture of the Sun taken in ordinary white visible light. You can see the larger sunspots for yourself (there are sometimes some tiny ones that are hard to see...) Dr. Craig DeForest

TELESCOPES (GROUND BASED)

QUESTION:
If one of the mirrors is smudged or cracked will it mess up the image that you are receiving?

ANSWER:
You betcha!! If it's just smudged, you'd get a lot of scattered light--as though you were wearing dirty glasses--and if it were broken it would be like looking through a couple of different telescopes at the same time. We take a LOT of care with the mirrors, and recoat them every couple of years.

QUESTION:
Do you need to replace parts such as mirrors often or once in a few years?

ANSWER:
We realuminize the mirrors every 2 years. This means we take them out and give them a fresh coat of aluminum, which makes them better able to reflect light. Unless there is a disaster, we never replace these parts.

QUESTION:
What lenses are used to look at the Sun?

ANSWER:
We actually use mirrors more than lenses. We can make bigger mirrors! There are lenses in the instruments attached to the telescopes. We use custom-built ones, achromats, convex, concave, etc.

QUESTION:
What is the size of the Kitt Peak and Sacramento Peak NM telescopes and their focal length?

ANSWER:
The McMath Pierce Telescope on Kitt Peak has an aperture of 1.51 meters and focal length of 82.62 meters. The Kitt Peak vacuum telescope has an aperture of 0.7 meters and a focal length of 36.4 meters. The Dunn telescope at Sac Peak has an aperture of 0.76 m and a focal length of 180 feet

TEMPERATURE OF THE SUN

QUESTION:
How do you measure the temperature of the Sun? Ms. Hammonds' Class Rancho Santa Fe, CA

ANSWER:
Hmmm... That's a good question. We can't put a thermometer on the surface of the Sun, but we can detect the color it glows at. Whenever anything in the universe is heated, it glows at a particular color that doesn't depend on what the stuff is made of. So a red-hot coal is the same temperature as a red-hot stove, which is the same temperature as anything else that's glowing that particular color of red. We can measure the exact color of the surface of the Sun and that tells us very precisely what temperature it is. The surface of the Sun is just under 6,000 degrees Kelvin, which is about 5,727 degrees Centigrade. I'll leave it to you to convert that to Fahrenheit! Craig DeForest

QUESTION:
Are any stars as hot as the Sun? Justin

ANSWER:
Yes, lots of stars are as hot as the Sun. We can tell how hot each star is by the particular color it glows. Hotter stars glow bluer, while cooler stars glow redder. One of my favorite stars, Betelgeuse, is much cooler than the Sun--it's a very deep red color. You can see Betelgeuse late at night: it's part of the Orion constellation. The very brightest star in the night sky is Vega, which shines with a bright blue light. It's much hotter than our sun, which is about 6,000 degrees Kelvin (5,727 degrees Celsius) at the surface You convert that to Fahrenheit! Cheers, Dr. Craig DeForest

QUESTION:
How hot is the Sun? How hot will the Sun get?

ANSWER:
The Sun is different temperatures in different places. In its core, where fusion is occurring the temperatures are around 15 million K. The temperatures go down as you go outwards until you reach the photosphere (the Sun's surface). There the temperature is about 5500 K. As you go out further into the Sun's atmosphere the temperatures increase again. The corona (the Sun's outer atmosphere) is a few million degrees. We are not sure exactly how it is heated. We think it has to do with the Sun's magnetic field.

QUESTION:
How would our Earth be affected if our Sun was a blue star? What about if it was a different color?

ANSWER:
If the Sun was a blue star, we would not be living on the earth. Blue stars are A) Very large (100 times bigger than our Sun) and B) very hot (Surface temperature of 50,000 degrees, 10 times hotter than our Sun). It would be way too hot for liquid water and life on Earth. The color of a star indicates it's temperature. Blue are the hottest, yellow (like the Sun) in the middle), and red the coolest. With a red star, these are also enormous, so the Earth's orbit would actually be inside the star.

QUESTION:
How did the Sun get so hot? Taylor, Mrs.Hammonds

ANSWER:
The Sun is powered by nuclear fusion, a process by which smaller nuclei (the center of atoms) are smashed together to form bigger nuclei. energy (a lot of energy!) is given off in this process and this powers the Sun. It is also the same process that is used in hydrogen bombs. Jack.

QUESTION:
If the Sun is really so hot, why isn't it's color blue, like the blue center of a hot flame here on Earth?

ANSWER:
The Sun isn't quiet that hot. Some stars are though. If you look at the stars in the sky you can find some that are blue. Also, there are different reasons why things glow in particular colors. sometimes the color is a good measure of how hot something is. Sometimes, though, things glow in particular colors because of energy transitions in certain atoms. I don't know exactly what happens to make the blue color in flames.

QUESTION:
How quickly would a bar of steel burn up when it hit the Sun? Lindy, Ms. Hammond's fifth grade class, Rancho Santa Fe School

ANSWER:
It would vaporize long before it even hit the Sun's surface.

QUESTION:
Why are the different layers of gas on the Sun different temperatures?

ANSWER:
That is a very good question, and the answer is no-one knows! There are a lot of theories around as to why the different layers of the solar atmosphere have different temperatures. SOHO is designed to look at the different layers of the solar atmosphere and try to find evidence for the mechanisms that, may heat the solar atmosphere. So in short, we don't know at present, but we have a lot of theories and a lot of data to help us answer these questions.

QUESTION:
How does NASA know how hot the core of the Sun is?

ANSWER:
We have a general idea just from a physical model based on the Sun's size and mass and the fact that the only energy source we know of that could be fueling it is solar fusion. We can make calculations based on those facts and figure out how hot it must be. Also, though, we can now probe the inside of the Sun with something called helioseismolgy. This is the study of how the Sun vibrates. You can tell things about the insides of the Sun, like its density and temperature, by studying these vibrations, just like you can tell about how big a bell is by listening to it.

QUESTION:
Why are the colors of the Sun that we see, yellow and red? Bo, 6th grade, Hydesville School, Hydesville, CA

ANSWER:
The Sun glows mainly greeny-yellow. We see it against the blue sky during the day so (if we look at it at all, which we shouldn't without special protection!) it appears yellow by comparison to the blue. At sunrise and sunset, it appears red for the same reason the sky appears blue! When sunlight goes through the atmosphere, some of the blue part of the light (and less of the green part) gets scattered in all directions, which makes the sky appear blue (the sky is bright because of the scattered light). At sunrise and sunset, you're seeing light that has travelled through a LOT of air, so most of the blue and green part is gone. The light that's left is reddish.

QUESTION:
Could the temperature difference between the Sun's surface and the surrounding space be caused by the continual loss of heat through convection and the lack of matter to absorb the energy producing a layer of unused radiation.

ANSWER:
What we are trying to explain on the Sun is that the Corona, the Sun's outer atmosphere is hotter than we would expect. We need to figure out how it can be hotter than the photosphere beneath it. You seem to be suggesting that the Sun is losing energy because it is being radiated away. We can't heat the corona to millions of degrees with radiation from the photosphere at 5500 degrees K.

QUESTION:
In regards to an earlier question about heat radiating away from the Sun you said that the Sun's surface can't heat the outer layer hotter than itself but why do you assume that it is the surface which is heating the outer layer

ANSWER:
I am simply ruling out that possibility (it seemed to be what you were suggesting), and that is how it would have to be if the corona were being heated by radiation from below. Actually we think the heating is being done by the magnetic field somehow.

TRACE SPACECRAFT

QUESTION:
If the Sun is so hot why doesn't it melt TRACE?

ANSWER:
TRACE is up in space and it constantly points the front end of the telescope towards the Sun. So the front of TRACE does get quite hot. There is no air up there to cool it or to spread the heat over the whole satellite. The front part is covered with blankets of "multi-layer insulation," sheets of plastic and aluminum foil. These reflect most of the Sun's heat back into space and keep the satellite from getting too hot. Of course, we couldn't put insulation over the open face of the telescope where the light enters it. So these openings have special filters which let in the light we want to study but which reflect most of the other light and heat back into space. By the way, the back of the satellite is always in the shade and so it gets very cold, about -80 degrees F. So it is also covered with insulation and has electric heaters under the blankets to keep it warm. Designing insulation and heaters for satellites is a tricky job done by specialists called thermal engineers. Susan Morrison was the thermal engineer for TRACE, and she did a great job.

QUESTION:
Why haven't we seen more footage from TRACE in the national media?

ANSWER:
A few bits have been on TV over the past year. There are several TV shows coming out this spring which will have more. Watch for "The Savage Sun" and "The Planets" on various cable channels.