POWERFUL radio waves beamed up into the sky have created artificially enhanced auroras visible to the naked eye.
Natural auroras, or the northern and southern lights, occur at high latitudes where Earth鈥檚 magnetic field funnels the charged particles that stream out of the sun into the ionosphere. About 100 kilometres above Earth鈥檚 surface, these particles collide with atoms and molecules in the atmosphere, boosting the energy of their electrons. The electrons return to their initial states by emitting light. Oxygen molecules, for example, glow red, while oxygen atoms produce green, and nitrogen produces blue.
杏吧原创s knew they could get the same effect with radio waves, but previous attempts to beam energy into the sky produced a feeble light that could only be detected by sensitive instruments.
Advertisement
Now Todd Pedersen from the Air Force Research Laboratory in Massachusetts and Elizabeth Gerken of Cornell University in Ithaca, New York, have created emissions of 鈥渦nprecedented brightness鈥�, using pulses of radio waves sent from a base station in Alaska. 鈥淭he beam is more like a flashlight than a laser,鈥� says Pedersen. 鈥淭he total power is about the same as large shortwave transmitters like the BBC鈥檚.鈥� The emission took the form of bright green speckles within a natural aurora (Nature, vol 433, p 498).
