 Greetings and welcome to the Introduction to Astronomy. In this week's Exploration of the Solar System, we are going to talk about the Luna 15 and Luna 16 spacecraft sent to explore the Moon. So what were these craft? Well, Luna 15 and 16 were both sample return missions. In other words, they were sending a craft to the Moon to pick up a sample and return that back here to Earth. Luna 15 was an attempted landing on July 21st of 1969, which failed. Now, if that sounds very familiar, yes, that is around the time of the Apollo 11 mission and in fact the same time as the Apollo 11 astronauts were walking on the Moon. So at that time the Soviet Union, not quite prepared to land on the Moon, was working on getting samples of the Moon and attempting to return those to Earth. Now the Luna 16 craft was successful, so this was a successful return mission and it was also the first lunar night landing. Now we have to recall that a night on the Moon lasts two weeks, as does a day. So it's not day and night as we think of here. The Moon rotates far slower than Earth and therefore a day on the Moon is a month of Earth time. Now this one landed in September of 1970 and was able to drill down about one foot into the lunar soil. Why drill down? Well, you want to get rid of any contaminants on the surface. You would not expect any biological contaminants, but we want to get what's underneath and that preserved material, not that which is exposed to the Sun. It collected about three and a half ounces or a tenth of a kilogram of lunar material, which was then returned to Earth about four days later. What kind of material was it found to be? Well, much like we found with the Apollo samples, it was a dark basalt, or volcanic rock, present on the Moon. So we're starting to learn now that the Moon has had a volcanic history and while it has not been volcanically active for a long time, we do still see the remnants of that in the samples that have been returned from, for example, Luna 16 and the Apollo missions. So let's summarize a little bit about these two and what we looked at. These were planned robotic sample return missions to bring material back to Earth. Luna 15 unsuccessful and did not land correctly. Luna 16 did return one tenth of a kilogram of lunar material to Earth for future study. Again, it was found to be dark basaltic, the volcanic material, similar to that which had been returned by the Apollo missions. So that concludes this lecture on the Luna 15 and 16 spacecraft. We'll be back again next week for another exploration of the solar system. So until then, have a great day, everyone, and I will see you in class.