Final answer:
Radio interferometry is easier because radio waves' longer wavelengths make combining signals to increase resolution more feasible compared with the shorter wavelengths of visible light.
Step-by-step explanation:
Interferometry is easier to carry out with radio telescopes than with optical telescopes because radio waves have much longer wavelengths, which presents challenges in achieving high resolution through single radio dishes. These challenges are overcome in radio astronomy by linking two or more radio telescopes together electronically, forming what is known as an interferometer. This enables sharpened images by combining the received signals, increasing effective aperture, and thus resolution. While recent technological advances have made visible-light interferometry possible, it is more difficult due to the shorter wavelengths involved, which require higher precision in the alignment and combination of light waves from different telescopes.