On Dec. 17, 2012, NASA's twin GRAIL spacecraft were deliberately crashed into the lunar surface traveling at nearly 4,000 mph. Another NASA spacecraft, Lunar Reconnaissance Orbiter, observed the impact using its LAMP instrument. The vertical rectangle in the animation represents the field-of-view of the LAMP instrument as determined by a thin slit-like aperture. LAMP is an imaging spectrometer so when looking directly down the slit sweeps across the lunar surface in what is call push-broom technique. The spacecraft rolled off to the side to put the slit on the lunar horizon. The LRO spacecraft crossed over the impact site at the right time for the first plume to get into the LAMP field-of-view.