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nulls spell out ATA
An image of “ATA” written in nulls across the sky; this illustrates the accurate nulling capability Allen Telescope Array developers have achieved.
Stanford professor and SETI pioneer, Ron Bracewell first proposed a nulling infrared interferometer to find planets around nearby stars in the 1970s. Radio astronomers had no idea then that this property could be used in such an advantageous way for SETI and radio astronomy. An array of a very large number of telescopes, it turns out, can be manipulated to form blind spots or "nulls" at other places on the sky.

As research and development on the Allen Telescope Array progressed, an unexpected capability emerged. Large numbers of small dishes could manufacture an arbitrary number of nulls with unprecedented accuracy and little degradation of the image beam during observations. Known sources of terrestrial interference (e.g. communications satellites) can be selectively screened out during observations, a huge boon to SETI researchers.

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