THROUGHOUT 2021, one of my mentors has had to remind me that this year wasn鈥檛 a good time to judge whether I like my job. After all, in the middle of a pandemic, no professor likes their job. An overstatement, perhaps, but probably not by much.
Despite all of this, my experience with teaching this fall reminded me of one thing that first drew me to becoming an academic: a life of learning. This semester, I taught an introduction to stellar astrophysics. In the process, I learned not just about teaching, but also some physics. So, as we finish another orbit around the sun and enter the third year of the coronavirus pandemic, let鈥檚 talk about a different kind of corona that I came to better understand this year: the solar corona and the problem it is giving scientists.
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Our local star is extremely average, and that is good news. If you had a diagram of the universe鈥檚 stars and their properties, the sun would be right in the middle. In other words, our sun is a good sample of the cosmic stellar population.
鈥淟et鈥檚 talk about a different kind of corona: the solar corona, and the problem it is giving us鈥�
This is great for science because the sun isn鈥檛 an experiment we can tweak. All we can do is observe. It is our good fortune that what we can learn by watching the sun is probably broadly applicable to lots of other stars too.
To say that the sun is average doesn鈥檛 mean it is boring or simple. The fact that it is more or less one gigantic nuclear fusion reactor is perhaps its most exciting feature. I have treasured talking to my students this year about how 鈥� through a combination of incredible heat and strange quantum effects 鈥� our sun transmutes hydrogen into helium, and in the process creates the photons that illuminate our planet.
In about 5 billion years, the sun will expand, transforming from the yellow star we know into a red giant possibly 100 times its current size, and burn some of that helium into carbon.
For now, though, we have a yellow star that has layers like an onion. Among these is the core, where the fusion happens. Then there is a convective zone where hot blobs of plasma move up and cold blobs sink.
Most interesting of all is the sun鈥檚 atmosphere, particularly a part of it called the corona. This is made of strands of plasma millions of kilometres long that look like flames dancing in a circle around the sun.
And here鈥檚 the thing: you would expect that the corona 鈥� being one of the outermost layers of the sun and so one of the furthest from the nuclear fusion in the core 鈥� would be relatively cool. Not so. The corona is 500 to 1000 times hotter than the sun鈥檚 surface. We have no idea why this is the case. This conundrum, called the coronal heating problem, is a major, unresolved puzzle.
As we head into 2022, I am excited about the possibility that one of my students will become interested in solving this problem. Even if not, I am hoping that by the time I come to teach this course again, I will be telling students about a fantastic discovery that has been made quite recently: the solution to the coronal heating problem.
