Date: February 14, 2012
Title: The Changing Sun
Podcasters: Rob Sparks & Matt Penn
Organization: National Optical Astronomy Observatory
Links: www.noao.edu
www.darksky.org
www.globeatnight.org
www.facebook.com/GLOBEatNight
twitter.com/GLOBEatNight
visiblesuns.blogspot.com/
eol.jsc.nasa.gov/earthobservatory/CITIES_AT_NIGHT_THE_VIEW_FROM_SPACE.HTM
Description: Sunspots have long been known to vary their numbers in an 11 year cycle. Recently we have made progress in understanding this process and have been collecting evidence that the cycle is not as constant as we might think. In this podcast, Dr. Matt Penn discusses some tantalizing clues that the Sun may be in for a change.
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 pens a great blog at halfastro.wordpress.com.
Matt Penn is an Associate Astronomer at the National Solar Observatory in Tucson, Arizona where he does research with the McMath-Pierce Solar Telescope.
Sponsor: This episode of the “365 Days of Astronomy” podcast is 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 of the National Optical Astronomy Observatory. I would like to welcome you to this episode of the 365 Days of Astronomy podcast. I am here today with Matt Penn of the National Solar Observatory. Good afternoon, Matt.
Matt: Hi, Rob, How’s it going?
Rob: Good, how about you?
Matt: Doing well.
Rob: Okay, first of all could you tell us a little bit about yourself and your background?
Matt: Right, I am a solar astronomer here at the National Solar Observatory and in particular I focus on studies at the McMacth-Pierce Solar Telescope at Kitt Peak. We study the Sun mostly in the infrared wavelengths and we measure the magnetic fields of sunspots.
Rob: We’re here to talk about sunspots. A couple of months ago I had Mark Giampapa on the podcast and he talked about the 11 year solar cycle. However, not all sunspot cycles are created equal, are they? So what are the properties that differ and how do they differ in these cycles?
Matt: We see that there is a lot of variation between cycles. The basic idea of a cycle is that it’s an 11 year cycle where the number of sunspots increases to a maximum and then decreases back down to a minimum. But it varies dramatically with the number of sunspots that appear during a cycle and the length of a sunspot cycle can vary dramatically as well.
Rob: And the magnetic field intensity of the sunspots can vary during these cycles as well?
Matt: Exactly. And that’s the thing that we’re finding at Kitt Peak with the McMcath-Pierce Telscope is that my colleague, Bill Livingston has made measurments of the magnetic fields of sunspots for 13 years now, and we he has found is that there is a surprising decrease, a linear trend in the strengths of magnetic fields in sunspots.
Rob: Wow! That’s kind of interesting. So these magnetic fields might actually go to zero if this linear trend continues.
Matt: Well, yeah, it’s surprising. What we have found, what Bill has found in his data is that there are no sunspots when the magnetic field is below 1500 Gauss and so instead of having a zero Gauss floor to the magnetic field in sunspots, it is actually 1500 Gauss. So you can imagine if this trend continues, extrapolating it into the future, it will clearly cross this threshold and we may end up with no sunspots. Now you know, just like the stock market, it’s very dangerous to extrapolate linear trends and so there is always a risk involved. We can say for sure what the Sun has been doing for the past thirteen years and we can say what would happen if it continues but we don’t know why it’s going on and we can’t prove that t will continue.
Rob: That’s always the difficult part: Will what’s happening now keep happening on the Sun? Our most recent solar minimum we just came out of a year or so ago was a fairly deep one. What have we learned from that and are there any questions still outstanding from that?
Matt: Right, the maximum of cycle 23 was a fairly normal maximum but then as we entered the decay phase, the Sun stayed in the quiescent phase for a long period and as a matter of fact the Sun dropped below levels of activity seen in the previous solar minimum. So between 22 and 23 and the minimum between 21 and 22, the Sun became very quiet between 23 and 24. We learned that the magnetic field in the interplanetary medium reached a very low value. We learned that the space environment reached levels of particularly low magnet field that had never been seen at before. Now why did that happen, we really don’t know. There’s some idea that maybe some of the dynamo processes inside that Sun that produce the magnetic field changed a little bit but we really don’t know the physics of why the solar minimum between cycles 23 and 24 was so long.
Rob: But we are coming out of that now, so what does the current Sun look like? I know have had lots of sunspots but haven’t had lots of flares until, actually, fairly recently.
Matt: Right, in the past month we have seen some flares. Actually the first X-class flare happened in 2011, almost a year ago but we just had the second X-class flare, X-class being the most intense X-ray flare emitted by the Sun.
Rob: But that one didn’t send out a CME toward Earth so we didn’t get a lot of good aurora with that one.
Matt: Right, we got lucky with this most recent X-class flare. It was pointed off the western limb of the Sun and so other planets were in the path.
Rob: I think that one went toward Mars roughly if I remember correctly.
Matt: I am not sure but luckily it missed us!
Rob: So what are the current ideas on the intensity of this cycle and possibly the next couple of cycles. I mean, people are always trying to forecast so what are the current forecasts and ideas?
Matt: Right, well if you look at the statistics, we have gone through 24 cycles so far and you can build up some statistical base during that and then make predictions from that perspective. Using those statistics, people have predicted amplitudes roughly in line with cycle 23, so cycle 24 and 25 are supposed to be about the same amplitude peaking at a sunspot number roughly identical to cycle 23.
Rob: Was cycle 23 above normal, below normal, about normal?
Matt: Well, cycle 23 was roughly normal for the past century. We have been in a period where the sunspot cycles have been more energetic in recent times. Cycle 23 was pretty typical for the 1900s. Now if we use the decaying magnetic fields that we observe on the Sun and sunspots on the Sun and use to predict what will occur during the next cycle, we predict that cycle 24 would only be about half the size of cycle 23. Using a different indicator, using the polar magnetic fields on the Sun, we can use that to predict that the amplitude for cycle 24 would be about half of cycle 23.
Rob: So you have got a couple of lines of evidence saying it might be weaker.
Matt: Exactly. And furthermore, radio emission from the Sun is on track with that prediction. That is, radio emission that we can observe every day comes from the magnetic fields of the Sun and the atmosphere of the Sun is on track to peak at roughly half the size, half the scale of cycle 23. So from all indications it looks like cycle 24 is going to be a wimpy cycle. Now again these are all predictions. We don’t really understand the basic physics that goes into that so its dangerous but it’s the best job we can do right now.
Rob: So cycle 24 is forecast to reach a peak in what, 2013 last I heard?
Matt: There are lots of ways to look at when the peak of cycle 24 might occur. My favorite way is to look at what is called the butterfly diagram. That is during every sunspot cycle, sunspots appear near the poles or mid-latitudes on the Sun and then they migrate toward the equator on the Sun following a pattern that if you plot it on a map looks like the wings of a butterfly. If we do that for the early spots of cycle 24 it looks like the peak might not occur until the middle of 2014, much later than people have been predicting. Some predictions have been 2012 and 2013, but with the long minimum between cycles 23 and 24 it’s really hard to understand when the maximum is going to be.
Rob: I have sent the predictions keep getting pushed back. Is there anything else we can learn about sunspots and what is your current research and what would you like to look at next?
Matt: What we are doing is trying to continue our measurements of the magnetic field and in particular look for supporting evidence in other lines of data. We found that if we look at flows on the Sun, there are indicators of the next sunspot cycle, cycle 25 being a little strange in that we don’t see the normal flows underneath the surface of the Sun. Furthermore, if we look at the corona, how the solar atmosphere varies with time, there are also indicators that cycle 25 might be a little weird. It’s not following the same pattern we saw in cycles 22, 23 and 24. If we extrapolate our magnetic field measurements of sunspots, we may not see any magnetic fields forming dark umbra, forming dark sunspots. So we are continuing this research, of course it will take many years to keep building up statistics, but we are hoping to understand why this might occur and what might be changing magnetic fields in sunspots on the Sun.
Rob: Thanks for joining me today. I would love to have you back in a couple of years and see how this all plays out.
Matt: Exactly, we are all interested and hopefully we will have more physical understanding of what’s going on.
Rob: Thanks for joining me today, Matt.
Matt: My pleasure.
Rob: This is Rob Sparks for the 365 Days of Astronomy Podcast. Thanks for listening.
End of podcast:
365 Days of Astronomy
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