When I look at the Moon, I do not immediately look towards the sea of Tranquillity where Apollo 11 landed, but towards a nearby region called Taurus-Littrow.

It borders the eastern shore of what is called the Sea of Serenity. Taurus-Littrow is on a tongue of lunar highland that separates the Sea of Serenity from the Sea of Tranquillity.

The Apollo landing sites can be seen by telescope

Of all the places where man touched down on the Moon, the general region of the Apollo 17 Taurus-Littrow landing site is the easiest to see through a telescope.

The exact valley, however, is elusive. It needs a high power and still observing conditions.

But when the night air is calm and the Moon stops shimmering for a few moments, you can zoom in and peer down on the last place where man walked upon the Moon.

His name was Gene Cernan, and he and geologist-astronaut Harrison Schmitt had just explored Taurus-Littrow and ended an era.

Completing his final moonwalk, Cernan grabbed the TV camera and pointed it at his lunar craft's front landing gear.

Here was a plaque with words that sounded so final. He removed the cover and read the message:

"Here man completed his first explorations of the Moon, December 1972."

He went on to add, "This is our commemoration that will be here until someone like us, until some of you who are out there, who are the promise of the future, come back to read it again."

With one last look around, he climbed on to the ladder to make his way into the lunar spacecraft to begin his journey home. The Earth was high in the south-western lunar sky.

A closed ambition

After the triumph of Apollo 11, it was clear that things were changing. At an Apollo 11 party, President Nixon said: "Here's to the Apollo programme. It's all over."

The jubilant celebrations after Apollo 11 were never repeated

In a way he was right. Apollo was a closed ambition - the ambition that had been put into words by President Kennedy: "Before this decade is out to land a man on the Moon and return him safely to the Earth."

Having achieved that great goal, many could not see what else there was to do. You wouldn't ask Lindbergh to fly the Atlantic again, it was said.

When Armstrong, Aldrin and Collins returned, Nasa had enough hardware for nine more landings, leading up to a grand finale: Apollo 20 was to stage a landing in the dramatic Copernicus crater.

It looked easier than it was. Later in 1969, Apollo 12 descended into the Ocean of Storms.

When Pete Conrad stood on the surface he looked into the mid-distance. There, 180 metres (600 feet) away, on the slope of an ancient crater, was Surveyor 3 that had landed two and a half years earlier.

When Apollo 12 returned, Apollo 20 had been cancelled, and 18 and 19 looked uncertain.

The crisis that gripped the world

Public interest was low as the Apollo 13 mission took off.

But people soon began to take notice as it became clear that an explosion on board made this the only expedition to the Moon that had suffered a catastrophic failure.

The damaged Apollo 13 revived public interest

The drama that followed gripped the world. The crew clung on to life through the 87 long hours that followed the explosion.

The interior temperature in Apollo 13 dropped to that of a refrigerator, and the cold seeped through the crew's thin flight suits. Despite fatigue and lack of sleep, in a wet and clammy capsule, they made it through the fiery re-entry and limped home.

But when they returned, the White House let it be known that space exploration no longer held such a high position in the national list of priorities.

Nixon was reducing America's global responsibilities as it faced new limits on its resources and will. The "pay any price, bear any burden" attitude of Kennedy-Johnson was over. Inflation was unchecked.

Nasa's head, Tom Paine, resigned. The hopes of a manned flight to Mars were gone, and the space shuttle and space station were in peril.

The final missions

Apollo was wound down, and the final three Moon landings of the project - to some, the most exciting - were cancelled.

But, in winding up the mission, four more rockets were to fly to the Moon.

Apollo 14 landed in the Fra Mauro highlands, touching down on material ejected billions of years ago from the great Imbrium basin, 640 kilometres (400 miles) to the north.

The cold Moon is alone again

With mission 15, the Apollo programme really hit its stride. It landed near a vast chasm in the lunar surface called Hadley Rille.

During a moonwalk, David Scott saw a small white rock which he immediately recognised as anorthosite - part of the Moon's primordial crust, the so-called genesis rock 4.5 billion years old.

Apollo 16 touched down in the central highlands, and Apollo 17 in a steep walled canyon.

And then it was over. The cold, grey Moon was alone again.

One flight controller back on Earth remarked that it must have felt the same when they finished the Pyramids.