So the sun is pretty constant, right? It sets. It rises. It shines. It doesn’t really change.
Actually, not quite.
The sun has about an eleven year cycle in which it goes from being more active to less active. Activity is measured in things like solar flares and sunspots. For this, we’re just going to be looking at sunspots. They are spots that are a lot darker (and cooler) than the surrounding areas on the sun; there are more of them when the sun is more active. They’re visible through a telescope with a solar filter, or special telescopes made for looking at the sun (do not look at the sun with the naked eye or through a telescope without a filter: eye damage results!).
Sunspot counts generally vary with that eleven year cycle, and some cycles are more active than others, kind of like some winters are snowier and some summers are hotter. Here’s a graph I took from a textbook:
Sunspots over time. Taken from The Cosmic Perspective: The Solar System, page 480.
Now you’re probably staring at that really low point between 1645 and 1715 with almost no sunspots wondering what the heck is going on. You are definitely not the first person to wonder this. Scientists have given this period a name: the Maunder minimum. It’s a “Grand Minima”, separate from the normal minima (low points) that show up every eleven or so years.
If the sun has an eleven year cycle, why not a second cycle that runs on a much longer timescale and has a much more drastic result? It’s hard to know how long that timescale is, because there is only so much data to go on. If the timescale is, say, a thousand years, we simply haven’t been observing the sun long enough to see that pattern emerge.
Still, something is going on during the Maunder minimum. If you look at the graph, the start of the Maunder minimum seems pretty sudden, but then sunspot numbers gradually return to normal. It is possible to create a computer model of the sun’s behavior that does that, but other models show a more gradual decrease in sunspot numbers. Unfortunately, we do not have any other Grand Minima like the Maunder minimum to work with. Since the Maunder minimum is so important in making models of the sun and how it works, any data about it becomes really important as well; it’s our only data point for modelling the sun’s Grand Minima and long-term cycles.
Data about sunspots is what the paper for this week concerns. “Revisited sunspot data: A new scenario for the onset of the Maunder minimum” by José M. Vaquero, M.C. Gallego, Ilya G. Usoskin, and Gennady A. Kovaltsov appeared in 2011 in Astrophysical Journal Letters. I would like to stress that I took no part in this research: all credit goes to the authors. I am simply explaining and summarizing the paper in more non-scientist friendly words and without getting into the details.
This paper was most concerned with the timeframe right before the Maunder minimum, 1635 to 1645, which was generally marked as high in terms of sunspots. This implied a sudden onset to the Maunder minimum; basically, the sun just got really quiet without a lot of warning.
Unfortunately, there was not a lot of data for the years 1636 to 1642, with little to no records. However, some more data was found tucked away in an archive! That was data from a German astronomer, Georg Marcgraf, and it was added into the data set. Some other data was eliminated because it was not based on direct observation but instead estimation. Additionally, a few points were corrected or deleted.
Armed with the new data set from the changes just mentioned, the data was run through a statistical evaluation that yielded a much smaller number than before for yearly sunspot averages. As I previously mentioned, it seemed that the Maunder minimum started with a drop in solar activity only a few years prior, but then took several years to build back up. These results imply that solar activity began dropping off two cycles before the Maunder minimum began. It changes how we might look at Grand Minima; not as something sudden, but as something that begins slowly, over time, just as they end. This affects our understanding of the sun’s behavior, the behavior of Grand Minima, and the models that study the sun’s activity and patterns. Which is pretty important, considering the effect the sun has in our lives. That’s a lot of impact for one short paper, but good data goes a long way!
These are sources I used directly to write this summary. The article cites many more references.
Bennett, Jeffrey et al. The Cosmic Perspective: The Solar System. 7th ed. San Francisco: Addison Wesley. Print.
Used for the graph at the beginning of my summary, and for background on the sun, sunspots, solar cycles, and other similar things.
Vaquero, José M., et al. “Revisited sunspot data: a new scenario for the onset of the Maunder minimum.” The Astrophysical Journal Letters 731.2 (2011): L24.
The main paper for today! The main text is only about four pages, with some figures and tables after the pages of references.