What astronomical technique was necessary to resolve the surface details of the red supergiant Betelgeuse?

Ground-based interferometry and specialized instruments

Because Betelgeuse is over four light-years away, conventional imaging is insufficient to resolve surface features. To achieve the necessary angular resolution capable of distinguishing surface patterns on such a distant, albeit evolved, giant star, astronomers employed advanced observational techniques. Specifically, ground-based interferometry, often utilizing facilities like those at the European Southern Observatory (ESO), was required. Interferometry combines the light from multiple separate telescopes to simulate the resolving power of a single, much larger telescope, allowing scientists to overcome the limitations imposed by distance and resolve features comparable in size to entire orbits within our own solar system.