In the left image we see a small portion of the Sun in regular, white light. It reveals a surface covered in dark patches known as sunspots – or, in other words, the Sun’s version of acne. The number of sunspots visible on our Sun at any point in time is highly correlated with the star’s 11 year period of solar activity. In the years when the Sun is quieter, we do not see as many active features like sunspots and flares, and, consequently, get less impressive northern light displays. On the other hand, when the Sun is more lively and vivacious, we see more acne and radiation storms.
These blemishes are a sign of an active Sun. The image on the right shows the arcs and loops of magnetic field lines on the Sun as observed in extreme ultraviolet light. Sunspots appear where the lines are crowded together into active regions with a strong magnetic field. The pressure of this strong magnetic field can cause the temperature of the area to decrease and the light to fade, which is why the sunspots appear dark – relatively. A sunspot by itself, not near the rest of the Sun in a nighttime sky, would appear brighter than the Full Moon!
These sunspots are dim and cold when compared with the rest of the Sun, yes, but when you are using the brightest, most brilliant object in the Solar System as your base of comparison, everything else is inevitably going to fall a bit short. This is the same reason we do not label everyone smaller than Yao Ming as tiny. Comparing heights with one of the tallest men alive is an exercise in futility, even for a person taller than average.
While certainly chillier than the Sun’s average surface temperature of 5,500° Celsius, a sunspot is actually rather hot when compared to what we are used to here on Earth. They usually clock in with a temperature around 2700-3700° Celsius. The hottest, industrial furnaces at cremation centers turn bodies to ash at a little less than 1000° Celsius, so, when it comes to our tolerance levels and perspective, sunspots are beyond sweltering.
In this case, first impressions are deceiving, appearances are dependent on surroundings, and there is not a single part of the Sun that is cool enough not to be ridiculously hot.
Image 1&2 Credit: Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams
