The Far Side of the Moon!

Happy New Year seems to be the best way to start the first blog of the year, and already what a start! So much has happened in astronomy and space exploration!

On the 1st of January we finally got to see the high resolution photos of the bizarrely shaped snowman-esque Ultima-Thule asteroid. Then, on the 3rd of January, the chinese lander Chang’e-4 landed on the far side of the moon. There are also really exciting things happening at Virgin Galactic, and it won't be long until space flight is much more accessible to many. I say many and not all...yet! And all of this within the first week of the year! The Chinese lander Chang’e-4 is the one that has excited me the most!

First, a bombshell: the excellent Pink Floyd album The Dark Side of the Moon is not actually about the moon, but more about the stresses and lunacy of everyday life. I have been living in blissful ignorance of this! I guess we should also address the title, The Dark Side of the Moon. This implies that one side of the moon is always in shadow and one side in light. This isn’t the case. It refers instead to the fact that only one face of the moon faces Earth.

The planet Thia, colliding with Earth, the debris from this collision is thought of of formed our moon!

The moon was created 4.5 billions years ago, around 20-100 million years after the solar system. The solar system at this point would have been a chaotic, violent pinball machine, where hundreds of planets were playing a massive game of chicken. A planet, Thia, collided with Earth,

its core combining with our own planet to eject a mass of material into orbit.

Over millions of years this material, with a little help from gravity, clumped to form our own little satellite: the moon! The iconic image of the ‘man in the moon’, the massive lava flows which make up the traces on our moon’s face, are a reminder of this turbulent beginning.

Our Satellite, the features that make up the moons 'face' are lava flows, not craters!

The moon and Earth are bound to each other gravitationally, a force resulting in the product of the Earth and Moon’s mass. The same force keeps the system ‘glued’ together. The only reason it is the moon orbiting us rather than the other way around is because we are more massive! We do experience this force on Earth and it’s no more visible than in the effect it has on our massive bodies of water.

The gravitational attraction due to the moon creates our tide. The Moon ‘locks’ the water in place and the Earth effectively rotates underneath. The frictional force between the Earth’s surface and the water is causing the rate of rotation of the Earth to decrease or, more simply put, the water is slowing down the rate at which the earth spins! So yes, our days are getting longer!

However, angular momentum must be conserved! Angular momentum is much like linear momentum, which is a product of the object's mass and velocity. Now, if the Earth’s momentum is decreasing, then something in the system has to increase. This is the moon’s angular momentum. An increase in the Moon’s angular momentum propels it to a higher orbit.

The result of this is that the moon is locked into what’s called a synchronous orbit. The time it takes to spin through its own axis is (roughly) equal to the time it takes to move around the Earth. The result… the near side of the moon is always facing the Earth and the darkside, or more appropriately the far side, of the moon is cast to face outwards, away from Earth.

The images being beamed to Earth from Chang’e-4 is a view of the moon that was not seen until 1959, when Soviet orbiter Luna 3 orbited the moon and is a view that only 27 people have laid eyes upon. That image of the chang’e-4’ lander photographing the roverand its its tracks, leading away from the lander off to explore, is going to be one of those iconic images of Luna exploration. It really was one of those hair tingling moments. Fingers crossed for the rest of 2019.

Get a bit close to our nearest neighbour at one of our events, check out our events page at or email us at to arrange a Practical Astronomy Workshop.

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