NASA Light Echoes Used to Study Protoplanetary Disks

This illustration shows a star surrounded by a protoplanetary disk. A new study uses data from NASA's Spitzer Space Telescope and four ground-based telescopes to determine the distance from a star to the inner rim of its surrounding protoplanetary disk. Researchers used a method called "photo-reverberation," also known as "light echoes. via NASA http://www.nasa.gov/image-feature/light-echoes-used-to-study-protoplanetary-disks