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Very Large Array (VLA)

The VLA is a radio synthesis telescope working in the wavelength regime from 7 mm to 90 cm. It consists of 27 25-m antenna, arranged in an upside-down "Y"-shape. Although in operation already for more than 25 years, this is still the most powerful radio interferometer working in the centimetre to decimetre wavelength regime. The fact that 27 antennas yield 351 correlations (combinations of one antenna signal with another) at any time makes it extremely sensitive.

I have taken so many photos of the VLA that I could open up a dedicated VLA public relations webpage. One problem in displaying it is that, even in its most compact configuration (see photo above), it is so big that showing all 27 antennae at the same time is difficult. One must take a photo from such a long distance that the single dishes then look miniscule (see above). But there is at least one aerial photo on the VLA website. In its largest configuration, with maximum antenna separations of up to 32 km, attempts to picture the entire array are quite hopeless...

Once in about 4 months the VLA changes from one of its 4 standard configurations to another. Antenna moves are facilitated with the help of a transporter (photo below). Basically, the array is used as a Y with different sizes. Depending on the size, it can resolve different levels of detail on the sky (the larger the better). But because a larger array also loses more information on extended sources on the sky than a small one, it is not possible to just go for the largest configuration and ignore the rest. Instead, combining data from the different possible configurations into one dataset provides the best images.

For example, the radio continuum image of the edge-on galaxy NGC 891 is a result of combining the data from two observations using different array configurations (the smallest and the next bigger one). In order to resolve yet more detail, one would need to re-observe the galaxy with the next larger configuration as well, and so on.

Here an overview of the entire array with its 27 antennas, plus the spare in front of the maintenance hall (on the far right).

Below a view of one of the VLA's three arms, with a typical late-summer afternoon thunderstorm in the background.

A view of the central array, where the telescope density, especially in the most compact configuration that is shown here, is highest.

And finally a view along the VLA's north arm, from the south. Here one can see how the transporter, after travelling along the straight railtrack, forks off to pick up an antenna from its pedestal.