How does the Very Long Baseline Array achieve extremely fine resolution?

The Very Long Baseline Array (VLBA) achieves extremely fine resolution—as sharp as 0.0001 arc second—by functioning as a massive radio interferometer. Unlike arrays where antennas are physically linked, the VLBA consists of ten 25-metre dishes spread across the United States, from the Virgin Islands to Hawaii, with no direct connections between them.1

To achieve its high resolution, the system relies on the following processes:

• Independent Recording: Each antenna records radio signals onto high-density computer disk drives. These drives are then transported to a central processing facility in New Mexico for playback and analysis to form images.1
• Precise Timing: Because the antennas are separated by vast distances, maintaining synchronization is critical. Each site uses a hydrogen maser atomic clock to ensure the precise timing required to correlate the signals accurately.1
• Interferometry: By combining these signals, the array simulates the resolving power of a single, enormous telescope spanning the distance between the antennas, allowing it to study compact radio sources with detail far exceeding that of optical telescopes like the Hubble Space Telescope.1