This interactive is used in Chapter 24.
Einstein predicted that gravity could bend light, and soon after, observations of star positions near a solar eclipse proved him right. It’s called gravitational lensing. You can experiment with the conditions and variables that create different effects in this Interactive. How do the mass of the “lens”, and its position and distance, change the shape, size, and position of an object’s image? See for yourself, and be sure to check out the presets that are real images, including the “Einstein Ring” named in the great theoretician’s honor.