Kistiakowsky and his team armed the device shortly after 5am and retreated to the control bunker.

Their final task was to switch on a string of lights on the ground that would serve as an ‘aiming point’.

The air force wanted to know what the effect of the blast would be on a B-29 30,000 feet up and some miles away.

In case of an accident, Groves left Oppenheimer in the control bunkers and joined Bush and Conant at base camp another 5 miles to the south.

There they picked up the countdown by FM radio.

Those in shelters heard it over the PA system.

Some of the scientists were with a party of onlookers 20 miles away on Compania Hill.

Teller said, ‘We were told to lie down on the sand, turn our faces away from the blast and bury our heads in our arms. No one complied. We were determined to look the beast in the eye.’

However, though it was not yet dawn, they smothered their faces with suntan lotion.

Teller himself wore a pair of dark glasses and heavy gloves and pressed a welder’s glass to his face.

At precisely 5:30am on Monday, 16 July 1945, the atomic age began.

As the firing circuit closed, 32 detonators fired around the outside of the high-explosive shell.

The shockwave produced hit the tamper, squeezing and liquefying it.

The plutonium sphere inside shrank to the size of an eyeball.

In the centre, polonium alphas kicked neutrons from the beryllium – one, two, maybe as many as nine of them.

This was enough to start a chain reaction in the plutonium.

It went through 80 generations in millionths of a second, generating millions of degrees of heat and millions of pounds of pressure.

The X-rays given off super-heated the air, generating another shock wave.

The explosion vaporized the tower and turned the asphalt around the base into green sand.

The bomb released approximately 18.6 kilotons of power, and the New Mexico sky was suddenly brighter than many suns.

Some observers suffered temporary blindness even though they looked at the brilliant light through smoked glass.

Here’s an eyewitness account:

Trinity Test, July 16, 1945 Eyewitness Report by Victor Weisskopf, an Austrian-born American theoretical physicist, one of the giants of 20th century physics.

He died in 2002, aged 93.

You have asked me to submit to you an eye witness account of the explosion. I was located at base camp and watched the phenomenon from a little ridge about 100 yds. east of the water tower. Groups of observers had arranged small wooden sticks at a distance of 10 yds. from our observation place in order to estimate the size of the explosion. They were arranged so that their distance corresponded to 1000 ft. at zero point. I looked at the explosion through the dark glass, but I have provided for an indirect view of the landscape in order to see the deflected light.

When the explosion went off, I was first dazzled by this indirect light which was much stronger than I anticipated, and I was not able to concentrate upon the view through the dark glass and missed, therefore, the first stages of the explosion. When I was able to look through the dark glass I saw flames and smoke of an estimated diameter of 1000 yds. which was slowly decreasing in brightness seemingly due to more smoke development. At the same time it rose slightly above the surface. After about three seconds its intensity was so low I could remove the dark glass and look at it directly. Then I saw a reddish glowing smoke ball rising with a thick stem of dark brown color. This smoke ball was surrounded by a blue glow which clearly indicated a strong radioactivity and was certainly due to the gamma rays emitted by the cloud into the surrounding air. At that moment the cloud had about 1000 billions of curies of radioactivity whose radiation must have produced the blue glow.

The first two or three seconds, I felt very strongly the heat radiation all over the exposed parts of my body. The part of my retina which was exposed to the indirect light from the surrounding mountains was completely blinded and I could feel traces of the after image 30 minutes after the shock.

The reddish cloud darkened after about 10 or 20 seconds and rose rather rapidly leaving behind a thick stem of dark brown smoke. After this, I remember having seen a white hemisphere rising above the clouds in continuation of the breakthrough of the explosion cloud through the ordinary cloud level. The path of the shock wave through the clouds was plainly visible as an expanding circle all over the sky where it was covered by clouds. After about 45 seconds the sound wave arrived and it struck me as being much weaker than anticipated.

V. Weisskopf

I watched a great interview from 1988 with Weisskopf where he said something I agree with.

He said a sunset is made ever more beautiful if you understand something about the science that causes it.

Science doesn’t deprive us of beauty – it enhances it.

A steel container weighing more than 200 tons, standing half a mile from Ground Zero, was knocked over.

As the orange and yellow fireball stretched up and spread, a second column, narrower than the first, rose and flattened into a mushroom shape, giving the atomic age a visual image that has become the very symbol of power and awesome destruction.

Later he recalled that the experience brought to his mind the legend of Prometheus, punished by Zeus for giving man fire.

He also thought fleetingly of Alfred Nobel’s vain hope that his discovery of dynamite would end wars.

Did you know the guy who created the Nobel Prize invented dynamite?

He also invented gelignite and ballistite, a predecessor of cordite.

He also owned Bofors, a company that manufactured cannon.

It was after he read a premature obituary which condemned him for profiting from the sales of arms, that he bequeathed his fortune to institute the Nobel Prizes.

Without telling his family!

At base camp, Bush, Conant and Groves shook hands.

Hubbard heard Groves say: ‘My faith in the human mind has been somewhat restored.’

Bainbridge said to Oppenheimer immediately after the test, “Now we are all sons of bitches.”

“My personal nightmare,” he later wrote, “was knowing that if the bomb didn’t go off or hangfired, I, as head of the test, would have to go to the tower first and seek to find out what had gone wrong.”

In the sweepstake, Isidor I. Rabi of the MIT’s Radiation Laboratory had put his money on 18 kilotons and swept the pot.

He broke out a bottle of whiskey and everyone had a swig.

The terrifying destructive power of atomic weapons and the uses to which they might be put were to haunt many of the scientists from the Manhattan Project for the rest of their lives.

But for the moment, the success of the Trinity test meant that a second type of atomic bomb could be readied for use against Japan.

Oppenheimer and Groves wrote a report for Stimson who was now in Potsdam with Truman.

Along with Little Boy, the untested uranium gun model Fat Man, a plutonium implosion device similar to that detonated at Trinity, now figured in American Far Eastern strategy.

Newspaper coverage that day did not enlighten the public.