The Westerbork Synthesis Radio Telescope (WSRT) consists of 14 dish-shaped antennas. These antennas can be individually directed at any point on the sky. Ten of the dishes have a fixed location, while two at the eastern end of the array can be moved on rails. 1.4 km to the east is a second pair of movable dishes on rails. Westerbork measures in wavelengths of 3.6 cm to 2.5 meter.
The aerial photo shows the configuration of the 14 dishes along an east-west line. In this view looking east, the last two movable antennas can just be seen in the open space at the upper left.
See antennas moving
To visit the Westerbork telescope, see the route description.
Each antenna has a diameter of 25m. You can get an impression of the size of each dish by comparing it with the little man standing under the image on the right.
In the entire area around the telescope the use of mobile telephones and other sources of radio interference (including automobiles) is prohibited. This is to minimize the undesirable effects of interfering signals.
A dish is like the lens of an optical telescope. It collects the energy from the entire surface area and concentrates it at the focus point. In the focus is the first part of the radio receiver, the so-called "frontend".
For maximum sensitivity, much of the frontend is cooled with helium to a temperature of 15 K (degrees above absolute zero). In degrees centigrade that is 258 degrees below 0 C (the freezing point of water).
On the right is a picture of the frontend , with the actual receiving antennas visible. The four brass rods (in the form of a cross around the central cylinder) pick up the radio signals, while the brass cylinder contains smaller antennas for receiving shorter wavelength signals.
By rotating part of the frontend it is possible to switch in receivers for various wavelengths:
See how this actually happens
There are five antenna systems available, each of which can observe at more than one wavelength. The combinations are: 3.6, 13 and 90 cm; 6 and 50 cm; 18-21 cm; 25-37 cm; and 70-110 cm.
The radio signal from the sky goes through thick coaxial cables to the main observatory building.
In the end, the coaxial cables from all 14 antennas come together in the control room. The operator in the control room has a good view of the dishes in the array. By means of a variety of computers it is possible for the operator to control the telescopes, receivers, and everything in the observing system.
In the control room are instruments, which convert the signals to digital information to be read and processed by a computer. The software that has been specially developed for this purpose is so clever that it makes the 14 dishes look like one large dish.
When the computer has completed its calculations, maps or images of astronomical objects are the result.
The WSRT can also observe together with other radio telescopes in Europe and in the rest of the world. In this way, the WSRT can produce such sharp images that a football on the moon would just be visible. A fantastic accomplishment!
Here are some example of radio images from WSRT :
(a dead star that has exploded)
Neutral hydrogen in a galaxy
Radio sources in a piece of sky
(every point is a radio source)
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