How does Earth’s rotation help radio interferometers make detailed images?

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Radio telescope Lovell Telescope, a fully steerable radio telescope at Jodrell Bank, Macclesfield, Cheshire, England.

Radio interferometers achieve high angular resolution by using aperture synthesis, a technique that effectively creates a much larger telescope from multiple smaller antennas.

As Earth rotates, the orientation and spacing of these antennas relative to a radio source change continuously. This movement allows the interferometer to sample a wide range of "Fourier components"—mathematical data points that represent the radio brightness distribution of the sky. By combining these samples over time, astronomers can synthesize the effect of a single, massive aperture, which would be physically impossible to construct.

This process, often called earth-rotation synthesis, enables the reconstruction of highly detailed images. Once the data is collected, high-speed computers perform a fast Fourier transform to convert these sampled components into a final, high-resolution image of the radio sky.1