LRO flies over the north pole of the Moon, where it has a very good view of the GRAIL impact. The second part is the view from LRO through LAMP's slit, showing the impact and the resulting plume. The orbits, impact locations, terrain, LAMP field of view, and starfield are accurately rendered.
The Gravity Recovery and Interior Laboratory (GRAIL) mission comprised a pair of satellites that together measured the gravity field of the Moon. GRAIL ended its mission with a planned impact into the side of a lunar mountain on December 17, 2012. Lunar Reconnaissance Orbiter (LRO) maneuvered into an orbit that would allow it to observe the impact. One of LRO's instruments, the Lyman-Alpha Mapping Project (LAMP), looked for the chemical signatures of a number of elements, including hydrogen and mercury, in the dust plume kicked up by the impact.
This animation shows the relative positions of GRAIL and LRO at the time of the impact, as well as the view from LAMP as it scanned for the dust plume. The LAMP sensor is a 6.0° x 0.3° slit that was positioned to look over the limb of the Moon, so that it would be pointed into the tenuous dust plume with only the sky in the background. This observation was possible, in part, because GRAIL impacted on the night side of the Moon, where there was no concern that LAMP's sensitive detector could be blinded by sunlit terrain. From Earth, the Moon was a waxing crescent at the time of the impact.