This is Death Valley in California, regularly the hottest place on the planet, and today the car says it's 111 degrees Fahrenheit, 45 degrees Celsius.

For centuries, the finest minds in science struggled to understand the origin of the sun's seemingly endless heat and energy.

What is it made of? Where did it come from? And what is the source of its phenomenal power?

Then, in 1838, British physicist John Herschel, took on the endeavour in his experimental attempt to catch a sunbeam.

So how much energy does fall on the surface of the Earth from the sun?

You can work it out with a beautifully simple experiment using only a thermometer, a tin full of water and an umbrella.

Basically, you let the water heat up in the tin to ambient temperature which, here in Death Valley today, is about 46 degrees Celsius.

And then you put the thermometer in the water, and you take the shade away and let the sun shine on the water. In direct sunlight, the water temperature begins to rise.

By timing how long it takes the sun to raise the water temperature by one degree Celsius, you can figure out exactly how much energy the sun has delivered into the can of water, and from that, how much energy is delivered to a square metre of the surface.

It turns out that, on a clear day when the sun is vertically overhead, that number is about a kilowatt.