Gas leaks, and the minuscule push provided by infra-red radiation from the crafts' electricity generators, were ruled out.

ECONOMIST: A space oddity

Even something too small to emit visible light will probably give off radio waves and infra-red radiation (Jupiter does).

ECONOMIST: X marks the spot

In a paper in this week's Nature, John Harries and his colleagues describe their analysis of the longwave infra-red radiation leaving the earth.

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Such so-called Dyson spheres would, if they exist, reradiate captured energy (after some of it had been put to good use) as heat infra-red radiation.

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By tuning the quantum cascade laser and measuring how much of the infra-red radiation is absorbed on its way to a detector, hazardous gases in between can be identified.

ECONOMIST: Lasers

The infra-red radiation emitted by the dust can also be used to measure the size of the ring directly, and this has been done using the Keck telescope on Mauna Kea, Hawaii.

ECONOMIST: Planetary formation

But the strength of the greenhouse effect depends on the chemical composition of the atmosphere, because the phenomenon is due to the absorption of infra-red radiation by various gases in the air.

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The other, which faces a specialised type of solar cell made of a material called indium gallium arsenide, is sculpted into a structure called a photonic crystal that causes it to emit infra-red radiation selectively at the frequency best absorbed by the cell.

ECONOMIST: Solar power

The red area represents the amount of radiation.

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