What Parts to Paint?   In order to look for an x-ray area-to-sunspot correlation you need to know what parts of each image to "paint." In the visible light images it's fairly obvious where the sunspots are, but what about the x-ray images?   What parts are x-ray active areas? The circled area in the sample image shows one of several active regions in the image. An active region is the site of strong magnetic fields spread out over a large area (perhaps as much as 50,000 km wide). When you are examining x-ray images, look for these concentrated bright white-to-yellow spots to indicate active regions. Paint all the active regions in each images, except those areas noted below.   A word about the colors Can you identify the active areas using the image colors? Remember: the colors are representations of light that our eyes cannot see. This means that any colors that appear in the images are the result of a decision by the person who created the image from a file of numbers: the numbers of x-rays in each pixel. For each type of image, there is a key, or standard, that identifies which color represents each number or range of numbers. What is important for your work is the fact that the same color choices were made for each of the x-ray images, and for each of the the white light images.   What doesn't count? Small "x-ray bright spots" occur scattered all over the sun, as opposed to the larger "active regions" which are concentrated closer to the equator. The bright points are now thought mainly to be places where small amounts of magnetic fields are being sucked down below the photosphere.   What about areas outside the disk? Large projecting magnetic loops like this, may appear as bright as the active areas. However, sunspots can be seen only on the solar disk, so we want to count only the active areas that can be seen within the boundaries of the disk.   For more information on the loops, plumes, and various other features you see in x-ray images, you can go to this page in the archive of Yohkoh images: SXT image features. (new window opens) ©Copyright 2001 Regents of the University of California.