Terry Kucera WebChat March 5

GHS: Welcome, John and Frank: we hope you'll be chatting next week. It's just 2 oíclock, so letís throw the Chat open to questions from any of the teachers and students who are with them...

GHS: We found this a.m. that folks tended to join in process, so let me just start the ball rolling by asking Terry if SOHO is returning science data 100% AOK at the moment.

Terry Kucera: At the moment SOHO is just starting up again after a "roll maneuver". In general, it is not in as good a shape as it was before we lost it last summer. Most of the instruments are still in pretty good shape, though, and some were not harmed at all.

Eileen Bendixsen: What was the diameter of the largest sunspot?

Terry Kucera: I donít know about the largest. I think the largest ones would probably be 4 Earth diameters across. A Sunspot region (a group of sunspots) would be even larger.

Eileen Bendixsen: In your BIO you talked about working with solar radio data. What is solar radio data?

Terry Kucera: In astronomy we study the entire spectrum of light from radio waves to gamma rays. The Sun gives off strong radio signals and you can study those radio waves to learn about the Sun. You can even make pictures of what the Sun looks like in radio waves.

Eileen Bendixsen: What was the most interesting observation made by SOHO?

Terry Kucera: I donít think there is any one most interesting observation! Very recently we had some interesting observations related to the solar wind. Scientists using SOHO data were able to observe material flowing up from the Sunís lower atmosphere in coronal holes and at the edges of convection cells in other parts of the Sun. This gives us clues about where the solar wind comes from.

Dominic: How much hotter is the temperature where SOHO is?

Terry Kucera: Because SOHO is out in space with no atmosphere around it, the temperature is very different depending on if you are facing the Sun or not. On the parts of the spacecraft facing the Sun it is pretty hot, while the parts facing away are quite cold. I canít remember the exact temperatures at the moment, but I believe most of the SOHO instruments operate at temperatures which you would consider relatively cold. I should also point out that SOHO is not really much closer to the Sun than the Earth is (as solar-system type distances go, that is).

Eileen Bendixsen: If the Sun is so hot, how could there be steam in the area of the sunspots?

Terry Kucera: The areas where there have been measurements of steam are, just a few thousand degrees. I donít remember the exact temperature, but certainly below the 6000 K of the photosphere outside of sunspots. In the relatively cool sunspot areas there are places where it is still not hot enough for the water molecules to completely come apart.

Dominic: What got you interested in researching the Sun?

Terry Kucera: What got me interested in studying the Sun? Well, it was partly chance. You have to specialize in something in graduate school. I also liked the idea that the Sun was a Star, but close enough to observe well and that it affects us.

Charlie Lindgren: I put a lab together using magnetogram images and continuum images. I said to treat the continuum as visible light. How wrong was that idea?

Terry Kucera: "Continuum" generally means a part of the spectrum over a broad wavelength range which is not dominated by particular spectral lines. In the case that you are talking about the "continuum" images are made in visible wavelengths of light, so they are "visible" images as well.

Charlie Lindgren: Super. I had the kids superimpose the visible over the magnetogram and see the relationship. Then we animated the images. It really worked well.

GHS: OK, weíve got a lot of new students joining: nowís the time for lots of new questions to Terry!

Dominic: How well does the Sunís spectrum fit a black body curve?

Terry Kucera: Black body curve: for the most part pretty well, I think, but not completely.

GHS: Terryófor those who arenít as up on space physics, whatís a black body curve?

Terry Kucera: Black body curves: Well, I think Iíll start with a simple explanation, which is to say that a black body curve is the spectrum you get from an object which is glowing because it is hot. In this case the hotter something is, the higher the peak wavelength of the curve is. This is related to why a stove top burner turns red when it gets hot. Molten steel is even hotter -white hot. You can tell how hot a star is by its color because they are basically black bodies.

The official definition of a black body is that it absorbs all the light that falls on it. That means any light it emits is an indication of the temperature of the object.

Dominic: What is the focal length of the telescope on SOHO?

Terry Kucera: There are a bunch of telescopes on SOHO. I know the SUMER spectrograph has a focal length of 1302.77 mm. EIT has an effective focal length of 1654.2 cm. (I have a book listing these things here.)

Charleston MS: from Megan: How old were you when you first got interested in the Sun?

Terry Kucera: I was probably about 8 years old when I first got interested in astronomy. I remember being interested in the Sun when I was in high school, but I think other things in astronomy are just as interesting.

Charleston MS: from Angelina: Did you think of being a scientist ever since you were little?

Terry Kucera: I was interested in science when I was little, but I didnít necessarily think I would be a scientist. For a while I thought I would be a physical therapist like my mother, until I found out that I would have to cut up dead bodies in college! I considered other things too.

Charleston MS: from Crystal: Do you ever think about retiring from being a scientist?

Terry Kucera: Well, I suppose when I get much older, I may want to retire. I donít know yet. There is also the question about what I would do if I couldnít find a job as a scientist. I would have to get a job doing something else. I think about that sometimes, but Iíve put off deciding while I still get to do solar physics.

Charleston MS: from Krista: How long have you been a scientist?

Terry Kucera: Well, I suppose it would make sense to start counting from when I started my research job in graduate school, so that would be 10 years (wow!). I have been out of school and working full time as a scientist for 5.5 years now.

Eileen Bendixsen: Are there different names for regions on the Sun?

Terry Kucera: Yes! There are all sorts of different regions on the Sun. In visible light you mostly just see the bright photosphere and sunspots. The sunspots are groups called "sunspot regions" or "active regions". Each active region is given a number. If you look in other wavelengths of light, like the ultraviolet, you can see even more things. The active regions are bright in ultraviolet regions. You can also see dark areas near the Sunís poles called "coronal holes"

Charleston MS: From Tim McCollum: Terry, thanks so much for responding to our questions. Class has ended so weíre signing off.

Charlie Lindgren: One of my kids asked, "If when the N/S orientation of the sunspots switches occurs between solar maximums does N/S orientation of the solar poles also shift, as in Earthís wandering poles?"

Terry Kucera: The Sunís magnetic field is even more variable than the Earthís is. It flips completely north to south every 11 years. In between there are times when it would be very difficult to say if it even has simple north and south poles. (think of a big jumble of magnets) The N/S orientation of the Sunspot groups changes too, but that is a part of the overall change of the Sunís magnetic field.

Sheri Edwards: What do radio waves tell us that other aspects of the spectrum donít?

Terry Kucera: Well, as I mentioned, they are dark in visible light. In ultraviolet and X-rays, you see the Sunís atmosphere above them, which is bright. Radio waves are good for looking at some very high energy things which happen on the Sun, like solar flares. They also help us to observe shock waves produced by coronal mass ejectionsólarge bubbles of gas which blow off the Sun.

Charlie Lindgren: How do they come up with that numbering system for sunspots? Region 8427, for example. What does that mean?

Terry Kucera: They just number the regions in the order that they appear

GHS: Terry... itís just about 3 oíclock, which was the time we said weíd end. On behalf of all who logged in, MANY thanks for participating. The Chat will be edited and posted online. Goodbye to all, and thanks for participating! And all--be sure to see Art and Terry once more in the two upcoming LIVE FROM THE SUN programs. Bye all, and thanks!

Terry Kucera: If you want to see what the Sun looks like in lots of different wavelengths, you might like to see http://umbra.nascom.nasa.gov/images/latest.html

Eileen Bendixsen: Terry, thank you for answering our questions. My students really appreciated chatting with you and Art today.