Intensity interferometry—the correlation of spatially separated light intensities—has historically been an important tool for precision optical astronomical observations. However, due to the extremely narrow field of view and weak signal, its scope has been limited to studies of the morphology of very bright emission regions, such as determinations of angular diameters of nearby hot stars. We propose adding to the detector optics an adjustable path extension that creates a primary interference fringe for widely separated sources, allowing maximum source separations parametrically larger than the angular resolution. This extended-path intensity correlator (EPIC), augmented with advances in single-photon detectors and spectroscopic gratings that improve the signal-to-noise ratio, would enable ground-based astrometry at microarcsecond-level precision in a field of view as large as several arcseconds. EPIC has the potential to revolutionize astrophysical and cosmological observations requiring high-precision differential astrometry on sources of high surface brightness. We outline how EPIC can be employed to detect the astrometric wobble of Earth-like planets around Sun-like stars at tens to hundreds of parsecs and expect that EPIC’s larger field of view will expand the power of intensity interferometry to a broad range of astronomical applications.

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• Optical, UV, & IR astronomy
• Telescopes
• Extrasolar planets
• Stars
• Astronomical masses & mass distributions
• Optical interferometry