TODAY’S TOPIC-WHAT IS A SUNSPOT? Seeing over 60,000 people a year with my solar telescopes has taught me several things about the level of scientific understanding of the Sun in our country. Its almost non-existent, unfortunately…☺ Almost without exception, I get asked the same set of questions at every event. Anyone who has met me in person can tell you that I love to talk about science, especially the Sun so I am never at a loss for creative new ways to try and answer these questions in terms the average person (like me) can understand. Generally people’s attention span after asking a question is about 20 seconds before they go on to something else and trying to explain what a Sunspot is in 20 seconds is certainly daunting. I don’t want to spread misinformation by over simplifying it but I have to condense it down to something that can be spouted out in about the same time as a punchline on the Daily Show or folks just lose interest. My typical response at a crowded public event is “It’s a cooler area on the Sun’s surface caused by magnetic interactions”. I always yearn for more time so that people can fully grasp how amazingly beautiful and dynamic the Sun’s magnetic ferocity is but alas, I generally don’t get the opportunity. “What is a Sunspot?” cannot be fully answered in 20 seconds or even in 20 years with our current understanding. We know a lot about them but no one knows for sure all the details of what a sunspot is and anyone who says they do is mistaken. Here’s how I explain it. I may be way off base but this is my understanding from watching them for years and studying all the available data. The Sun, as covered in previous topics, is a giant ball of Hydrogen and Helium gas and plasma completely governed by the four forces of nature. Electromagnetism is at the forefront of these forces as far as observable features are concerned and sunspots are no different. When the Sun’s magnetic field lines get twisted and tangled in a multipolar configuration (solar maximum), it is quite common for these field lines to erupt through the Sun’s photosphere and cause a host of observable phenomena. Sometimes, several dozen of these highly energetic and strongly charged field lines share a common polarity and a common highly localized base, or enrty/exit point in the Sun’s surface. When this happens you end up with a large area (many times larger than the Earth sometimes) of similar polarity field lines grouped together like an old sailors twisted rope. These lines become forced together through unimaginably strong magnetic forces and create an area so large that the Sun’s normal convective flow of energy cannot escape out of that area of the photosphere. It is very similar to trying to force a cork into a fire hose ejecting water at full speed. It is exactly the same as when you were in grammar school and tried to force two magnets together at their North ends and they pushed away from each other. Imagine several million 10,000km high magnets all being held together at their North ends and you standing in the center of this trying to send an electrical signal out of it. Aint gonna happen…☺ These spots become a lot cooler than the surrounding area and appear darker in our telescopes. Why, because telescopes especially narrowband telescopes see light and where there is an absence of light, it appears to be darker. This doesn’t mean that there is a hole in the Sun like some news outlets would like you to think, it just means that there is no light of that particular frequency exiting the area into your telescope. The spots are also recessed into the photosphere of the Sun as discussed last week in the topic “The Wilson Effect”. Some say that this is unexplained but from my viewings it seems obvious to me that the rest of the photosphere is raised higher than these cool areas because of the pressure of the exiting convective cells. Of course, I’m an amateur hobbyist like you so I am probably mistaken. Spots are comprised of two distinct regions. The Umbra, is the dark central core of the spot and the Penumbra, which is the usually associated gray area around the spot that appears to have distinct fibral structures. The umbra indicates a vertical set of field lines and the penumbra indicates where these field lines are at angles less than vertical around the edges of the spots. Some of the most beautiful sketches and images of our star are of these penumbral areas. (see below) Sunspots are always formed in pairs of opposite polarity and are almost always seen between 20-60 degrees latitude for some reason as of yet unexplained. It appears to be associated with the flow of plasma in the underlying convective zone. Sunspot groupings are almost always the source of large events on the Sun but sometimes they just sit there and do nothing… Sunspots are magnificently vibrant features as well and they are constantly changing shape, splitting apart of joining together and sometimes completely disappearing or re-appearing as they march across the face of the Sun. This combined with the Sun’s rotation as discussed in previous topics can lead to some enchanting natural ballets on the photosphere. Sunspots generally appear only during periods of maximum magnetic disruption of the Sun’s poles (solar maximum) and they can last for several solar rotations or form and be gone in just a few hours. Folks, thank you for reading this topic! You don’t have to invest much to safely view Sunspots in your own backyard and watch the majesty of these features just like the ancient Chinese, Mayans or many Europeans did during the renaissance. All it takes is a piece of white paper as a screen and a box with a pinhole in it aimed at the Sun! Or you can do like my friends and invest a fortune in it to get every detail possible out of the images… Either way, you’re a solar scientist. this link will take you to an amazing movie from NASA SDO of a sunspot group churning across the Sun...:) sdo.gsfc.nasa.gov/assets/gallery/movies/Spots_grow_best.mov
Posted on: Mon, 05 Aug 2013 15:22:27 +0000
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