An eye on the radio sky
The Westerbork Synthesis Radio Telescope (WSRT) is a linear array of fourteen 25-meter radio telescopes. The dishes are arranged along a 2.7-kilometer east-west line. Ten of the telescopes are fixed in position, while four are movable along railway tracks, allowing astronomers to change the telescope's configuration for different observations. Completed in 1970, the WSRT uses a technique called aperture synthesis. By combining the signals from all individual dishes, the array functions as a single, much larger telescope, capable of producing high-resolution images of the radio sky.
The telescope's design is distinct. Unlike many modern radio telescopes that use an alt-azimuth mount, the WSRT dishes have an equatorial mount. This design keeps the detectors at a constant orientation to the sky during an observation, which is particularly effective for research on polarized radio waves. The observatory operates across a wide range of frequencies, from 120 MHz to 8.3 GHz. The WSRT is operated by ASTRON, the Netherlands Institute for Radio Astronomy, and it frequently participates in Very Long Baseline Interferometry (VLBI) observations, linking with telescopes worldwide to create a virtual Earth-sized instrument.
From hydrogen maps to fast radio bursts
The WSRT has made significant contributions to radio astronomy. It was originally designed to map the distribution of neutral hydrogen, the most abundant element in the universe, across the northern sky. These surveys provided detailed views of the structure of the Milky Way and other nearby galaxies.
A major upgrade completed in 2019, the APERture Tile In Focus (Apertif) project, replaced the original detectors with focal-plane arrays. This new technology increased the telescope's field of view by a factor of 25, transforming it into a powerful survey instrument. With the Apertif system, the WSRT can now map vast areas of the sky much faster than before, enabling large-scale searches for pulsars and Fast Radio Bursts (FRBs).
The observatory is located on a site with a dark history. It was built on the grounds of the former Camp Westerbork, a Nazi transit camp during World War II. The location was chosen for its "radio quietness," essential for the telescope's sensitive receivers. The nearby Herinneringscentrum Kamp Westerbork (Camp Westerbork Memorial Center) details the site's history.