© GGOSVLBI – Very Long Baseline Interferometry
Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. Radio signals emitted by extragalactic sources (quasars: quasi-stellar radio sources, radio galaxies) are captured by a pair of directional antennas (radio telescopes) located on the Earth’s surface. Due to the different position of the antennas, the same signal arrives at each antenna with a slight time difference ranging from 0.003 to 0.050 seconds. This time delay is measured to a precision of few trillionth of one second (picosecond) with sophisticated atomic clocks installed at each antenna. By multiplying the time delay with the speed of light, the distance between the two antennas can be determined with an accuracy of few millimetres.
