Moon

The Moon is Earth's closest cosmic neighbor, orbiting at an average distance of 380,000 kilometers. Compared to Earth, the Moon's diameter is nearly four times smaller. Because of its synchronous rotation, commonly known as "tidal locking", the Moon consistently shows the same hemisphere to Earth. On the side facing Earth, visible even to the naked eye, are dark regions called lunar "seas" (maria), which are vast plains of solidified basalt lava, along with brighter highland areas. A prominent feature of the lunar surface is the abundance of craters, which can be observed through a small telescope. These craters are remnants of asteroid and comet impacts from the distant past. With no atmosphere to regulate its temperature, the Moon's surface can exceed 100°C on the sunlit side and drop below -200°C on the night side. Geologically, the Moon is inactive, with its surface remaining largely unchanged over millions of years. Aside from Earth, the Moon is the only celestial body where humans have set foot. US astronauts Neil Armstrong and Edwin Aldrin became the first humans to walk on the Moon on July 20, 1969.