Date: November 17, 2011
Title: Solar Cycles
Podcaster: Rob Sparks and Dr. Mark Giampapa
Organization: National Optical Astronomy Observatory
Link: http://www.noao.edu http://twitter.com/#!/NOAONorth www.facebook.com/USNOAO
Description: The significance of solar cycles
Bio: Rob Sparks is a science education specialist in the EPO group at NOAO and works on the Galileoscope project (www.galileoscope.org), providing design, dissemination and professional development. He also blogs at halfastro.wordpress.com.
Dr. Mark Giampapa is Deputy Director of the National Solar Observatory.
Sponsor: This episode of “365 Days of Astronomy” has been sponsored by the National Optical Astronomy Observatory. NOAO is a US national research and development center for ground-based nighttime astronomy. We provide astronomers access to world-class observing facilities on a peer-reviewed basis. Our mission is to engage in programs to develop the next generation of telescopes, instruments, and software tools necessary to enable exploration and investigation through the observable Universe. For information on observing proposals or our public programs, please visit www.noao.edu for more information.
Transcript:
Rob: Hi, this is Rob Sparks from the National Optical Astronomy Observatory. I would like to welcome you to this episode of the 365 Days of Astronomy podcast. So far this year, we have been looking at things mostly outside our solar system, but today I have Mark Giampapa from the National Solar Observatory here to talk with us about the Sun. Good morning, Mark.
Mark: Well, good morning, Rob and thanks for having me here.
Rob: You’re welcome. I apologize, my voice is a little out of sorts today. I have had a cold the last couple of days but fortunately, I am on the mend. First of all Mark, would you like to tell us a little bit about yourself and your research interest at the National Solar Observatory?
Mark: I am an astronomer and also serve as Deputy Director here at the National Solar Observatory in Tucson, Arizona. My primary research background is actually in stars, especially stars like the Sun and the study of magnetic activity on stars and all its manifestations, very much analogous to the types of activities we see on the Sun such as spots and flares and so on. I also study very low mass stars such as M dwarf stars and they are the major constituent of the stellar population of our galaxy and most people don’t appreciate that most stars in our galaxy are smaller and cooler than our own Sun.
Rob: Yeah, you always hear people say our Sun is an average star, but it’s actually quite a bit above average, isn’t it?
Mark: Yeah, I think when they say average in some sense if you take the average of largest and smallest stars in some sense you get something like the Sun, but the Sun is not average in the sense of being a typical star. It’s in the minority of maybe 5% of the stars in our galaxy.
Rob: Well, we are going to talk about solar cycles here today. So first of all, what is a solar cycle, what do we mean when we say that?
Mark: Well, historically what we meant when we say solar cycles is the sunspot cycle and that’s they approximately 11 year variation in sunspot numbers, that’s when we count the sunspots on the Sun. That in itself has a long history of the protocols and what the procedures are for counting spots. But never the less, we see that number vary in a periodic way about every 11 years, so that’s the sunspot cycle. That’s the most prominent manifestation of the solar cycle. The solar cycle is seen is other kinds of variations on the Sun, some of the bright magnetic features that we see also sort of wax and wane with the 11 year cycle and we see features in the Sun’s corona as well that also show that 11 year cycle.
Rob: Yes, I remember in ’99 when I saw a solar eclipse in Germany near solar max they talked about the corona was a little bit different than some of the other ones.
Mark: That’s true, the corona is an amazing place really, apart from the cycle. It’s two million degree temperature still represents a mystery to solar astronomers how the corona is formed and maintained. It is also the site of the most violent explosions in the solar system. With solar flares you have the equivalent of literally millions of Hiroshima type atomic bombs going off.
Rob: The current solar cycle we are in has started off rather slowly. Could you tell us what we know about the current solar cycle and its slow start?
Mark: Well, it’s been very unusual. We have what we call an extended solar minimum from the previous cycle. Cycles have a number since we started observing them, since Galileo started observing them, and the most recent one that was completed was cycle 23 and it lasted over 12 years and it was notable for the long period of quiescence, that is there wasn’t a lot of activity on the Sun and it had a large number of spotless days, not historically unprecedented but still it ranks up there with a large number of days with no spots on the Sun. So the Sun was unusually quite during this last minimum but as you said, we have now started up on cycle 24 and it seems like a bit of a week start. The Sun’s still hasn’t shown us many spots and other kinds of activity we might expect. There’s also some other indicators, more subtle indicators, that suggest we’re entering a rather weak cycle in cycle 24 and perhaps cycles following could be even weaker.
Rob: Yes, I think I heard something about something analogous to the jet stream on the Sun that predicts solar cycles?
Mark: Yes, that is correct, Rob. At the National Solar Observatory we operate a network called GONG, Global Oscillation Network Group, and it observes the subtle oscillations and vibrational modes, kind of analogous to little earthquakes on the Earth, and we observe those modes of oscillations and from them we are able to probe the very interior of the Sun from near the surface to near the core. The surface flows typically show what we call a jet stream near the surface that goes toward the poles and the jet stream forms during the current cycle and it heralds the next cycle and we have seen that the last couple of cycles, but this time is different. The jet stream has not formed or it may be there but it is there very weakly, very different from previous cycles so we don’t have that strong jet stream flowing toward the poles that would presage the next cycle, cycle 25.
Rob: So this is predicting that the next cycle might be much weaker or even non-existent might be one of the indications?
Mark: That’s one of the indications. We have another indication from my colleague Bill Livingston has been taking measurements with the McMath-Pierce Solar Telescope on Kitt Peak and they have been measuring the strengths of sunspot magnetic fields, that is in the darkest part of the sunspot, and they find the mean field strength, that is the average field strength of sunspots has been declining over the last 20 years and that trend is continuing. The prediction, if we extrapolate that is that sometime between 2020 or 2025 the spots would disappear if that trend continues. So that’s another piece of independent evidence that’s also implying weak solar activity ahead in terms of cycles and numbers of spots.
Rob: That will be interesting to see how that plays out. We had a period called the Maunder minimum that had no spots quite a while ago, didn’t we?
Mark: Yes, not too long after Galileo invented the telescope and turned it on the Sun to observe sunspots, there was a time when sunspots declined and then there was a 100 year period when no sunspots were observed on the Sun. And when that happened there was a period of cooling, at least in the northern hemisphere in Europe, and that suggested a correlation between sunspot activity and weather on the Earth, or climate on the Earth although the exact causes and mechanisms have not been identified still. It is still a subject of tremendous focused research.
Rob: It will be interesting to see how that plays out in the future as well. You also mentioned solar cycles on M dwarfs. Do other stars have cycles like our Sun? What’s your research in that area?
Mark: That’s a good question and an astronomer by the name of Owen Wilson in the 60’s asked exactly that question. So he began a monitoring program of monitoring stars in the neighborhood of the Sun of Sun-like stars and other types of stars like the red dwarves and he found a number of stars do exhibit cycles similar to the solar cycle on the Sun but in much great array of amplitudes and periods. Some are much shorter, some are quite a bit longer than 11 years, some stars show no cycles at all. They are just flat and we think that some of those stars could be candidates for Maunder minimum stars, stars that have entered this prolonged state of low variable activity on them. In my own research, I have been using a telescope on Kitt Peak, the WIYN 3.5 meter telescope, to look at a cluster called M67. M67 is an open cluster in Cancer that has about the same age and the same chemical abundances as our own Sun. So within this cluster there are many Sun-like stars. It’s a perfect solar laboratory if you will to study stars like the Sun. So I did a survey of what their activity levels were like in that cluster and I found most of the Solar like stars that overlapped with what we see in our own solar cycle. Some were much more quiet, had low solar levels, but some were in excess of what we see at solar maximum. So I got a good idea of the spread of activity in Sun-like stars which could indicate the potential range of variation in our own Sun from very quiet to very active.
Rob: That’s pretty interesting.
Mark: It was a very exciting project and I hope to follow it up someday with an actual monitoring program to actually see the cycles on those stars but that would take a big telescope dedicated for a long period of time.
Rob: That’s a great segue to the last question, I am going to ask you the famous blank check question. If you had a blank check to design your ideal research facility to answer your questions about solar cycles, what would you build?
Mark: Well, as you can guess from my answer to the last question, I would build a four to six meter telescope that has a large field and a multi-object spectrograph and imaging capability to look at stars in a number of clusters like M67 but also younger clusters and perhaps older clusters so I could see how the Sun might have evolved in its activity from when it was young to when it is old and the possible ranges of activities in other Sun-like stars. So I would love to have a facility like that. In some sense the other type of facility I would build already exists and that’s the Kepler Observatory in space that is looking for transits. But in addition to transits it’s seeing all sorts of stellar activity, all sorts of spot variations and so forth. So if you could run the Kepler mission for many years, I hope it does get extended for many years, that will yield a huge amount of data that will give us insight on the origin of activity like spots which are apparently deep within the star in a mechanism called the magnetic dynamo.
Rob: Yes, and there have been several podcasts on that so if you would like more information just look in the 365 Days of Astronomy podcast archive for more on the Kepler mission. Well, thank you for joining me today, Mark.
Mark: Well, thank you, Rob.
Rob: It’s been a pleasure and thanks for listening to this episode of the 365 Days of Astronomy podcast.
End of podcast:
365 Days of Astronomy
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