The Moon Has Been Earth's Companion for 4.5 Billion Years

Analysing lunar rocks brought back to Earth by Apollo astronauts suggests that our Moon formed just over 4.5 billion years ago.

It is widely believed by most scientists that the Moon, which is 3,474 kilometres (2,159 miles) in diameter, formed from ejected material thrown out into space when a planet roughly the size of Mars collided with the young Earth. It is thought that the collision may also be the reason the Earth is tilted on its axis by over 23 degrees. This tilt is responsible for the different seasons we witness on our planet each year.

The young Moon was a lot closer to the Earth back then, orbiting at an estimated distance of 20,000 to 30,000 kilometres (12,400 to 18,600 miles) from the surface of our planet, compared with today's average distance of 384,400 kilometres (238,855 miles). If mankind had been around then, can you imagine how big the Moon would have looked in the night sky?

At present, the Moon continues to move away from the Earth at about 3.8 centimetres (1.5 inches) per year, which is roughly the speed at which your fingernails grow. Over an average human lifetime, that amounts to 2.66 metres (8.75 feet). It doesn't seem much, but it shows how the kilometres and miles add up over millions or billions of years.

If we had no Moon, our day would be roughly 6 hours long. The effect the Moon has had on our tides has gradually slowed the Earth's rotation over billions of years. And if there were no Moon, the rise and fall of our tides would be significantly less, leaving only the gravity of the Sun to pull at our oceans.

The largest tides occur when the Earth, the Moon and the Sun are in alignment, and both the Moon's and the Sun's gravity are pulling at our oceans at the same time. Without the Moon, the evolutionary path of life on Earth may have been very different, and we humans might never have existed.

On 25 May 1961, American President John F. Kennedy announced the ambitious goal of sending men safely to the Moon and back. He said it would be achieved in less than ten years, but sadly he was not there to see it happen within his estimated timescale.

I remember driving home one evening in July 1969, parking my car and looking up at the Moon. It seemed so bright that night, and I was amazed that two men had landed safely, left their spacecraft and were walking on the moon's surface.

I felt so proud of humanity and so privileged to have been born at the right time to witness and understand that great event.

Apollo 11 was the first mission to land men on the Moon. It arrived there on 20 July 1969.

Three men made that journey. Michael Collins flew the command module Columbia, and he stayed in lunar orbit while Neil Armstrong and Buzz Aldrin made their way to the surface in the lunar module Eagle. It must have been a very long day for Michael. His biggest fear was the real possibility of going home alone.

Before their return home, Aldrin and Armstrong positioned a retroreflector (mirror) on the Moon's surface facing the Earth. Two more were added by Apollo 14 and Apollo 15. They are called the Lunar Laser Ranging Retroreflector Arrays. They have been in use ever since and are the only scientific experiments left operating from the Apollo programme.

A laser beam leaves the Earth, bounces off a mirror on the Moon and returns to Earth. By recording this measurement many times, scientists can calculate with remarkable accuracy how far away the Moon is and the rate at which it is moving away from the Earth each year.

A huge number of things could have gone wrong with the first Moon landing, from the launch and the journey to the Moon to the landing itself and the return to Earth.

In the event of a disaster, with two men stranded on the Moon, American President Richard Nixon had a speech prepared, but thankfully he never had to read it.

This is close to what he would have said.

"Fate has ordained that the men who went to the Moon to explore in peace will stay on the Moon to rest in peace. These brave men, Neil Armstrong and Edwin Aldrin, know that there is no hope for their recovery. But they also know that there is hope for mankind in their sacrifice. These two men are laying down their lives in mankind's most noble goal: the search for truth and understanding. They will be mourned by their family and friends; they will be mourned by their nation; they will be mourned by the people of the world; they will be mourned by a Mother Earth that dared send two of her sons into the unknown. In their exploration, they stirred the people of the world to feel as one; in their sacrifice, they bind more tightly the brotherhood of man. In ancient days, men looked at the stars and saw their heroes in the constellations. In modern times, we do much the same, but our heroes are epic men of flesh and blood. Others will follow and surely find their way home. Man's search will not be denied. But these men were the first, and they will remain the foremost in our hearts. For every human being that looks up at the Moon in the nights to come will know that there is some corner of another world that is forever mankind's."

Very brave men.

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