The Moon

The Moon is our closest neighbour and only natural satellite. It is probably one of the most obvious astronomical objects when it is in the sky. The Moon has been very important in human culture through the years but is also vital to life on Earth. It remains the only body outside of Earth, which humans have set foot on.

The Moon Credit: NASA

The Moon is about one third the size of the Earth and it is about 385,000 km away. It orbits once every 29 days but also spins once every 29 days. This results in us seeing the same size of the Moon all the time, a phenomena also called tidal locking. As the Moon orbits, we see different parts of the moon illuminated. I have another blog post about the phases here –

The Moon formed about 4.5 billion years ago. Scientists think that the Earth was struck by an object about the size of Mars. The result of the collision was a huge debris disk around the Earth which eventually clumped together to form the Moon.

The Moon has a solid, iron, rich core. This is surrounded by a liquid iron mantel which is then surrounded by the solid crust we see when we look at the Moon today. When you look up at the Moon today you will notice large dark patches. These are called “lunar seas” but are patches of basalt rock made when lava from volcanoes on the Moon poured out on the surface. There are no longer any active volcanoes on the Moon. You may also notice many craters on the surface. These were caused by impacts from meteorites. The Moon is always getting hit but most of the impacts date back to a period know as the late heavy bombardment. Close to full Moon you may notice bright rays extending from craters. This is the material that was ejected from the impact site.

The brighter areas of the Moon are know as highlands. As the Moon has been constantly hit by meteorites, the surface has been ground down to a fine powder called regolith. This caused particular problems for the astronauts in the Apollo missions. The finely ground material is silica rich which essentially means it’s glass. It got in every gap of the spacecraft and caused a lot of skin irritation. The remains the only other body in the Solar System that humans have set foot on. In July 1969, Neil Armstrong step foot on the Moon and became the first human to do so. He was followed by another 11 astronauts, during Apollo 12, 14, 15, 16 and 17. Eugene Cernan was the last person to walk on the Moon but plans are afoot for more crewed missions to the Moon so it is likely he will soon lose this place in history.

Harrison H. Schmitt during an EVA on Apollo 17 Credit : NASA

NASA are planning a crewed mission to the Moon in 2024. Although, Japan, China and Russia all plan to send humans to the Moon in the 2030s. The goal is to build a permanent lunar base on the Moon. Of course robotic spacecraft also study the Moon. The first to reach the Moon was Luna 2 which impacted the Moon intentionality in 1959. This was followed by many other missions over the years including orbiters, landers and rovers.

The Moon affects life on Earth and has been part of human culture for thousands of years. One of the most widely known effects is the tides. As the Earth spins, the water of the oceans, and indeed the land itself is pulled by the gravity of the Moon. This has the effect of causing tides. Another, less known effect is the effect on the climate. The Moon acts as a balance which prevents the tilt of the Earth from varying too much. If the Earth didn’t have the Moon to do this, the tilt of the Earth would change over time and create wild changes in climate. It is thought that the balancing effect of the moon and resulting long periods of climate stability was vital to complex life developing.

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