VLBI observing sessions typically last 24 hours. During this time, the radio telescopes point at a selection of radio sources and record their signals. The data recording process is visualised in the animation. The telescope slews to a radio source and receives the incoming signal. After completing a so-called scan, the telescope moves to the next radio source. The incoming signals are digitised using an analog-to-digital converter. This produces data at a rate of up to 8 gigabits per second.

A recording rate of 8 gigabits per second means 8 billion bits every second. That’s equivalent to about 1,700 books, assuming each book has 300 pages, 2,000 characters per page, and each character is represented by 8 bits. If each book is 3 centimetres thick, a stack of these books would be 51 metres high. So, to put it into perspective: Every second, VLBI generates data equivalent to a 51-metre-tall stack of books.

At the end of an experiment, around 30 terabytes of data are recorded. The data from all participating VLBI radio telescopes are then transferred to a central location. Here, the data are processed. A high-performance supercomputer aligns the recorded signals from all telescopes and derives a geodetic dataset in the form of delays.