Very Large Array, NM
While driving back from Texas in July of 2013, I had the opportunity to visit the Very Large Array Radio-telescope in New Mexico, USA.
The Very Large Array (VLA) is an astronomical observatory. The VLA consists of 27 dish-shaped antennas that are connected together to form a single radio telescope.
Astronomers use the VLA to study cosmic objects ranging from the Sun and planets of our solar system to distant galaxies and quasars at the edge of the observable universe.
Each antenna collects incoming radio waves emitted by cosmic objects and sends them to a central location where they are combined. By using many antennas in this manner, the VLA can make detailed pictures of cosmic objects. The VLA is one of the most powerful radio telescopes in the world today.
Antenna specifications: The type is an offset cassegrain with asymmetric subreflector. The mount is an Altitude-Azimuth. Focal Ratio: f/.35. Total weight: 235 Tons. Total height: 29 m when pointed straight up. Dish diameter: 25 m. Drive System: 4 electric motors (2/axis). Range of motion: 540 degrees azimuth, 120 degrees elevation. Tracking Accuracy: 15 arc seconds in winds up to 25 km/hr. Foundations: Height above track 1.9 m. depth below track 9.7 m.
Weak radio waves from celestial sources are collected by the highly directional antennas. The waves are focused into the receiver by the main dish, sub-reflector and feedhorns.
When a radio telescope is pointed toward a source, the radio waves hit it’s parabolic surface and are bounced up to the sub-reflector above the dish. The sub-reflector is movable, and it, in turn, focuses the waves into the aperture, or opening, that corresponds to the wavelength being observed. Pictured above is a “close-up” of the sub-reflector and the various apertures, or openings. The apertures are covered to keep “nature” out, but radio waves can pass right through the covers.
The wave passes through the aperture into the feed-horn. Pictured above, this is the horn for 21 cm wavelengths. It is in a room directly below the dish. There are eight feed-horns clustered in this room. The size of the feed-horn depends on the wavelength chosen for observing. Higher frequencies correspond to shorter wavelengths.
Because the radio signals are so faint, the receiver must be cooled by liquid helium to 15 degree Kelvin or minus 458 degrees Fahrenheit in order to reduce the internally generated noise which otherwise would mask the very weak radio signals from space.
Pictured above, the waves travel down through these cables I the center of the antenna structure and on into the antenna building. These weak signals are amplified several million times, converted to an intermediate frequency and carried to the Control Building via a buried waveguide transmission system.
These giant antennas, with 25 m diameter dishes, were specially designed for the VLA. The aluminum panels of the dish are formed into a parabolic surface accurated to 0.5 mm. Most of the time the antenna drive system is precisely tracking a radio source across the sky.
Pictured above, a VLA antenna turns in a circle to see all parts of the sky. It is called “turning in the azimuth”, which it does on a track, much like a railroad. It can turn 540 degrees before it must “unwind.” The track is shown below.
Pictured below, the antenna is tilted in elevation by these two 5-hp motors and this giant bull-gear.
The VLA array of 27 radio antennas span a huge “Y” shape (called the Wye). Every four months, they move antennas to different stations along each arm of the Wye. At its most compact configuration, the array has a wider field of view and maximum sensitivity to diffuse gas. At its most extended, thy zoom in on finer detail. For complex objects, such as the huge, knotty jets of gas shooting out of t radio galaxy Hercules A (pictured below), they combine perspectives to build a complete picture.
Pictured below, the VLA antennas are placed in four different configurations designated as A, B, C, and D. This allows astronomers to see either fine detail or large structure in regions of space. In the “A” configuration the antennas are “a” long way away from each other.
As you can see from the above images, the resolution of the VLA can be varied by changing the maximum spacing of the antennas. Resolution is the ability to discern details in a picture, and different resolution. Therefore, the antennas can be moved in and out on each arm. The effect is similar to a zoom lens on a camera.
Planning for the VLA began in the early 1960s, and by 1967 the design and the proposal to build the VLA were submitted to the National Science Foundation. Actual site work began in 1974, and first antenna was assembled at the VLA site in 1975. The VLA was completed in January of 1981 at a final cost of 78.6 million dollars.
Just east of Socorro, and nearby, is the infamous “Trinity” site from World War II. The nuclear age began with the detonation of the world’s first atomic bomb at the Trinity Site on July 16, 1945. The site may have been named Trinity by J. Robert Oppenheimer, director of the Los Alamos nuclear Physics laboratory, who said at the blast, “Now, I am become Death, the destroyer of worlds,” quoting from the Bhagavad Gita. The detonation of the bomb marked the culmination of the Manhattan Project.