What is the primary purpose of very long baseline interferometry (VLBI) in radio astronomy?

What is the primary purpose of very long baseline interferometry (VLBI) in radio astronomy?

• A. Improve timing calibration
• B. Determine relative motion of antennas on Earth
• C. Detect gravitational waves
• D. Map the cosmic microwave background

Answer: (B)

VLBI’s power comes from linking antennas across very large distances to act as a single, ultra-high-resolution telescope. The measured timing differences of a radio wave arriving at widely separated sites depend on the exact geometry of the array—the positions and motions of the antennas. Knowing how the antennas move and where they are lets you convert those timing differences into precise baselines, which is what unlocks extremely fine angular resolution and accurate positions of celestial radio sources. This geodetic capability—the precise determination of relative antenna motion and baseline geometry—forms a primary use of VLBI. While timing calibration, gravitational-wave searches, or mapping the CMB can involve related techniques, they’re not the central purpose of VLBI.

VLBI’s power comes from linking antennas across very large distances to act as a single, ultra-high-resolution telescope. The measured timing differences of a radio wave arriving at widely separated sites depend on the exact geometry of the array—the positions and motions of the antennas. Knowing how the antennas move and where they are lets you convert those timing differences into precise baselines, which is what unlocks extremely fine angular resolution and accurate positions of celestial radio sources. This geodetic capability—the precise determination of relative antenna motion and baseline geometry—forms a primary use of VLBI. While timing calibration, gravitational-wave searches, or mapping the CMB can involve related techniques, they’re not the central purpose of VLBI.