in space.

Actually, you don't have to. You can see it for yourself.

That was Starfish Prime,

the highest altitude nuclear test in history.

In 1962, the US government launched a 1.4 megaton bomb

from Johnston Island

and detonated it 400 km above the Pacific,

about as high as where the International Space Station

orbits today.

The detonation generated a giant fireball

and created a burst of energy called

an electromagnetic pulse, or EMP,

that expanded for over 1,000 km.

EMPs can cause a power surge,

damaging electronic equipment in the process.

And this one was no different.

Across Hawaii, streetlights went dark,

telephones went down,

and navigation and radar systems went out,

not to mention the six or so satellites that failed.

And all this came from a 1.4 megaton bomb.

Tsar Bomba,

which was the largest nuclear bomb that was ever detonated,

was 50 megatons.

So, what would happen if we detonated that

above the United States?

For starters, there's no atmosphere in space,

so there would be no mushroom-shaped cloud,

and no subsequent blast wave, or mass destruction.

Instead, you'd get a blinding fireball

four times the size of Starfish Prime's.

And if you look directly at it within the first 10 seconds,

you could permanently damage your eyes.

Satellites wouldn't be safe either.

Radiation from the explosion would fry

the circuits of hundreds of instruments

in low-Earth orbit,

including communication satellites,

military spy satellites,

and even science telescopes like the Hubble.

Plus, astronauts onboard the International Space Station

might be at risk of radiation poisoning.

On the ground, however, you'd probably be fine.

The detonation point would be far enough away

that the high energy radiation wouldn't reach you.

But don't get too comfortable.

Remember Starfish Prime's EMP?

This time the EMP would cover

one-third of the entire United States,

bringing down regional power grids and electronics,

like a lightning strike.

Millions of Americans will be out of power

for hours or even days.

But it's not all doom and gloom.

The radiation would also interact with

oxygen and nitrogen in the atmosphere

and create a spectacular aurora near the detonation site

that would last for days.

Now, let's be clear this will probably never happen.

Super thermonuclear devices like Tsar Bomba no longer exist.

And even if they did, the Tsar Bomba weighed

around 27,000 kg.

There are only a couple of operational rockets

in the world that can manage to lift

something that heavy into space in the first place.

So, we're probably safe

from that anyway.

This video was made in large part thanks

to the calculations from physicists

at Los Alamos National Lab.