The black disk is the occulting disk blocking out the disk of the Sun and the inner corona. The tick marks along the bottom of the image mark off units of the Sun's diameter. Procedure Have you students select a feature that can be seen in all five images, for instance the outermost extent of the bright structure or the inner edge of the dark loop shape. Measure its position in each image. Using the position and time, students can calculate the average velocity.
Velocity is defined as the rate of change of position.
Scientists often look at a number of points in different parts of the CME to get an overall idea of what is happening. Sometimes it can be tough to trace a particular feature. Further work SOHO observes many CMEs and this sort of exercise can be performed on other sets of images we have on the web. Students can measure their the velocities and accelerations too. This activity is based on Sun Centered Physics , a set of lesson plans developed by Linda Knisely.