Analysis of old data from Apollo seismometers may have revealed that the Moon has an iron core like Earth. The Apollo Passive Seismic Experiment consisted of four seismometers left on the Moon by astronauts. They were used to record both moonquakes and the impacts of spent rocket stages. New analysis suggests that the Moon has a solid inner core 150 km in diameter and a liquid iron outer core 205 km in diameter. NASA Press Release As followers of this blog know, data from the Lunar Laser Ranging Experiment, also left on the Moon by astronauts, may reveal a changing speed of light. As Galileo suggested, light can be timed using lanterns on distant hilltops. Galileo lacked an accurate clock, but today we have access to laser lanterns and the distant hilltop of the Moon. 40 years of laser ranging report the Moon receding anomalously high. If the speed of light were slowing, time for light to return from the Moon would increase each year, making the Moon appear to recede faster. Missions to the Moon are a priceless asset for cosmology.