We describe observations of the Earth and moon performed by the ultraviolet spectrograph (UVS) on the European Space Agency’s JUICE mission during a lunar-Earth flyby in 2024. JUICE-UVS observed UV sunlight reflected by the moon’s surface, and atmospheric emissions at the Earth. The observations provide the first opportunity to test the UVS response to planetary targets and demonstrate the types of measurements to be performed in the 2030s, when JUICE will explore Jupiter and its icy moons.