“Beyond Contact,” an O’Reilly book, is a serious study of the means by which humanity and aliens may be able to communicate, both up close and at lightspeed-laggy distances.

Monochromatic (single color) light is the signature of an artificial device. Naturally occurring light emitted by a star will always blur across many colors. The yellow-white light we see from our sun is actually a composite of red, orange, yellow, green, blue and violet light (plus ultraviolet and infrared light, which we cannot see). When we look at the sum of these colors together, the light is white. The laws of blackbody radiation, which we discussed previously as a way to measure temperature, govern this pattern.

By understanding these natural patterns, it is possible to engineer artificial signals that stand out against them; lasers are perfect tools for this. We can use lasers to generate an extremely strong and focused source of light tuned to a very precise wavelength (color). We can also use lasers to transmit extremely brief, but bright, pulses of light. The trick is to generate obviously artificial signals that stand out against the type of light normally emitted by a star.

Knowing how starlight usually behaves, it is possible to build an artificial beacon that, while it is weak compared to a star as a whole, shines brightly at a specific color or for very brief periods of time. The receiving party can then look for evidence of this type of artificial signal by splitting the light into thousands of individual colors, or by measuring the intensity of the light during very short (billionths of a second) timeframes.

Link Discuss (Thanks, Tim!)