An Unspotted Sun?
Published on Sep 3, 2008 at 2:35 pm.
6 Comments.
Filed under Sun, amusement.
Just for fun, Miki, from Rampup Solutions, sent me a link to this astronomy news spoof. I found it hilarious. However, it gives me something to blog about. This past month continued the unusually long period of extremely low solar activity that I had written about nearly two months ago.
The Sun has gone an unusually long time with very few sunspots. There have been very few sunspots since March. This is not the longest period without sunspots this century, but I agree that it does seem pretty long. This sunspot minimum has lasted between 1 and 3 years, depending on how you define minimum. When people look at sunspot number graphs, they often look at a graph lasting a century or so. Under that time scale, the minima look almost like sharp reversals on the graph. But, if you look at individual solar cycles, you see another pattern. The cycles tend to increase in activity much more rapidly than they decrease. Particularly at the end of a cycle, the number of sunspots very gradually drops off. It becomes very difficult to actually define when a minimum begins. Then end of the minimum is often easier to determine, since it often is accompanied by a rather sharp rise in the number of sunspots, with the average number of spots increasing for years. This current minimum is long, but not not excessively so, given that the 23rd Cycle just gradually tailed off. This is similar to the 20th Cycle, which had a protracted slow end, and thus a long sunspot minimum.
Humans tend to remember vividly the recent past, but the distant past tends to get blurred a bit. The last sunspot minimum ended right near the end of 1996. Given that the sunspot cycle lasts an average of 11 years, we shouldn’t really expect the new cycle to really get going strong until the end of last year, anyway. And roughly one third of the sunspot cycles are a year or so off of the average, and a 12 year cycle would only be the end of this year. So, this is not really a horribly long delay in getting the new cycle started. It just seems like an unusually long minimum because Cycle 23 dropped off and has has such a long period of low activity at its end. I’d say that it is still way too early to get out the parka with the expectation of the Sun cooling off.
Another thing about this minimum is that it is a particularly deep one. There has been very little solar activity at the minimum. After all of the unusually active activity of the latter half of Cycle 23, we’ve gotten used to the Sun being active, and we forget that over a decade ago, it was just like this: quiet. That fact stays with me, because I wrote a solar observational laboratory exercise for my students back in the early 1990s, when the Sun was quite active. But, by the mid 1990s, there were plenty of times when the Sun was blank, so we wound up abandoning doing the solar observations with our introductory astronomy students for a couple of years until the Sun started regularly having sunspots again.
At the top of the page, I linked to a posting about the very quiet Sun. It isn’t really fair to say that the Sun has had absolutely no spots this past month. In fact, it did have sunspots. Those sunspots, however, were very small, and often they didn’t last a long time, but they were there. The Solar Influences Data Analysis Center reports most days as having zero sunspots, but several days in August were listed as having several sunspots. NOAA’s Space Weather Operations reports just one sunspot for the month. This brings up another matter. How do you determine the number of sunspots? With today’s telescopes and equipment, we can detect a lot more subtle sunspots than could have been detected years ago. So, often the sunspot numbers reported are adjusted from what was actually recorded. This is an attempt to make the data collected today be something that can be compared with data collected decades or centuries ago. Unfortunately, I feel that the way used to convert todays observations to a standardized number that would correlate with what would have been recorded years ago probably fails at very lot sunspot numbers. I would imagine that when there are virtually no sunspots visible, the old visual observers may have peered more closely at the Sun and counted regions that may have been overlooked on days when the Sun was loaded with sunspots.
What this means, of course, is that even though we have close to four centuries of visible observations of the Sun, you have to be very careful when making comparisons of todays observations with those of a century or more ago (or even early in the Twentieth Century). So, I am not at all concerned that there is something wrong with the Sun, or that the sunspot minimum is indicating anything of enormous portent. Now, if the Sun still has virtually no sunspots by the end of next year, then I think that perhaps we should start to consider that something different is happening than has happened in nearly 300 years.
-Astroprof
Image courtesy NASA
Johnny Zornes on September 4, 2008 at 6:17 am: 1
“What this means, of course, is that even though we have close to four centuries of visible observations of the Sun, you have to be very careful when making comparisons of todays observations with those of a century or more ago (or even early in the Twentieth Century).”
I very much agree with this statement, however it seems to me that the sunspot count we now have is far greater than they were able to even guess at a century ago, skewing todays count to a higher number than previous observations. NASA’S Dr. Hathaway made a statement saying that todays sunspot count is within normal range of those in the past 2 centuries. I think that if we used past years visual observation techniques, the sunspot count nowadays would probably be one of the lowest on record.
Guy Grierson on September 8, 2008 at 4:59 pm: 2
The winter of 2006/7 was a very cold one in the northern hemisphere. When you take into account that sunspot minimum and the current cycle, does it lead you to suspect tha this winter could be relatively cold, considering the length and relative quietness of the minimum period?
Astroprof on September 8, 2008 at 6:12 pm: 3
The winter of 2006/7 was quite cold, I understand, for part of the northern hemisphere. It was actually a very warm one for us here in Texas. Often it takes many years for the cumulative effects of changes in the solar cycle to manifest itself. So, I don’t know that you can draw any particular conclusions about this winter. If the solar minimum lasts for several more years, though, then …
Tom on September 25, 2008 at 6:43 am: 4
The older visual observations are, in fact, entirely comparable with their modern counterparts (I write as a contributor to the official sunspot number record now maintained by SIDC). The technology and methods have not significantly changed, surprising as it may seem. And in any case we have an almost complete photographic record for most of the history of what is now called the International Sunspot Number since it was instituted by Wolf in the mid-nineteenth century. We know that the early observers ignored small spots, which is not the current practice, and that is why a correction factor is now applied to sunspot counts so as to preserve the comparability of the entire series.
Astroprof on September 25, 2008 at 11:51 am: 5
Tom,
I know about the correction factor. I did not say that you could not compare today’s observations with those of the past, only that you have to be very careful in doing that comparison. That is where a correction factor comes into play. However, I suspect that the correction works better with large sunspot numbers than it does with small sunspot numbers. That does not mean that old results for small numbers are inaccurate, only that some care needs to be taken when comparing them with current figures. The need to be able to compare numbers is why the methods of determining sunspot numbers have not evolved much over time, which is why comparisons are, indeed, valid.
John A. Jauregui on October 9, 2008 at 11:21 pm: 6
I just returned from visiting Yellowstone and was struck by the devastation of the 1988 fires, which were preceeded by acute drought and record setting dry lightening. I began to wonder what solar activity occured leading up the 1988 fire storms. Solar cycle 22 started just a couple of years before that summer of drought and dry lightening. Check this out. Relative to other cycles, that solar cycle had 1) a very fast rise time - 2.8 years, 2) a very short cycle length - 9.7 years, 3) a high minimum sun spot number - 12.3, and 4) a high maximum sun spot number - 158.5
more:
“Cycle 22 certainly provided us with many highlights. Early in the cycle the smoothed sunspot number (determined by the number of sunspots visible on the sun and used as the traditional measure of the cycle) climbed rapidly; in fact more rapidly than for any previously recorded cycle. This caused many to predict that it would eclipse Cycle 19 (peak sunspot number of 201) as the highest cycle on record. This was not to be as the sunspot number ceased climbing in early 1989 and reached a maximum in July of that year. Whilst not of record amplitude, Cycle 22 still rated as 4th of the recorded cycles and continued the run of recent large solar cycles (Cycles 18, 19 and 21 were all exceptional!). A very notable feature of Cycle 22 was that it had the shortest rise from minimum to maximum of any recorded cycle.”
Material Prepared by Richard Thompson. © Copyright IPS - Radio and Space Services.