# 2 Energy from the Sun

The Sun supplies the Earth with energy: radiation streams out at 385 trillion trillion W (385 followed by 24 zeros!). But as the Earth is 150 million km from the Sun (on average), it intercepts only a tiny fraction of this energy.

It’s like a garden sprinkler or fountain. A large flow of water is supplied to spray out in every direction, but each of the surrounding plants – or, in the case of the photograph of the unusual fountain in Figure 1, birds – receives only a small part.

Figure 1 Birds in the spray of the spherical El Alamein Fountain in Sydney.

- How many 10 W compact fluorescent light bulbs would be needed to create the same energy output as the Sun?

- The number of light bulbs needed will be the Sun's output, divided by the output of a single light bulb: so the answer is 38.5 trillion trillion. This is similar to the highest estimates for the number of stars in our Universe (1 trillion trillion).

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