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11-Very Large Array April 2022



4/24/22

Morning cold (29) at Datil campground, but began warming up quickly with lots of sunshine. Cindy made eggs for breakfast, then it was time to break camp and move on to our next stop.

On our way to Socorro, NM, stopped at the VAL project and took pics. Those dishes are massive.

Very Large Array from Very Large Array – National Radio Astronomy Observatory (nrao.edu)

VLA Basics

From the early 1960s at NRAO, astronomers knew they needed an array of radio dishes to complement the work of our giant, single-dish telescopes. An array is a group of several radio antennas observing together creating — in effect — a single telescope many miles across.

As a first step, NRAO built the Green Bank Interferometer to learn and develop the best communications, correlation, and atmospheric correction practices. Throughout the 1960s and 1970s, this four-element array helped NRAO prepare for a Very Large Array of 27 telescopes.

VLA Construction Timeline

Location

The first consideration before building any radio telescope is its location. Cosmic radio waves are billions of a billion times fainter than radio waves used to broadcast information on Earth. Radio telescopes must be placed where they can collect these faint cosmic radio waves without any radio interference from humans or nature.

The Plains of San Agustin in New Mexico, northwest of Socorro, is a flat stretch of desert far from major cities. The Plains are ringed by mountains, which act like a natural fortress of rock that keeps out much of the radio interference from cities, even hundreds of miles away.

The desert climate of the San Agustin Plain is critical to the success of the VLA. Humidity is a real problem in radio astronomy, because water molecules distort the radio waves passing through them and also give off their own radio waves that interfere with observations at certain frequencies. Radio telescopes that collect radio waves in the same frequencies as water’s radio waves need to be in deserts to reduce this background signal from Earth-based water molecules.

Design

Each of the VLA’s 28 antennas (including the one that is a spare) is an 82-foot dish with 8 receivers tucked inside. The dish moves on an altitude-azimuth mount, what you’ve probably seen as a classic tripod mount: it tilts up and down and spins around.

The iconic “Y” shape of the VLA is not for looks, it’s for function. The wider an array is, the bigger its eye is, and the more detail it can see out in space. The VLA’s unique shape gives us three nice long arms of nine telescopes each. It also gives us the flexibility of stretching the arms when we need to zoom in for more detail.

We put our telescopes on rails. Three times a year, a specially-designed rail truck, called a Transporter, picks up telescopes and hauls them one at a time farther down their track. Over the course of 16 months, the VLA lengthens each of its legs from two-thirds of a mile to 23 miles long.

VLA Science

The Very Large Array is the most versatile, widely-used radio telescope in the world. It can map large-scale structure of gas and molecular clouds and pinpoint ejections of plasma from supermassive black holes. It is the world’s first color camera for radio astronomy, thanks to its new suite of receivers and a supercomputer that can process wide fields of spectral data simultaneously. The VLA is also a high-precision spacecraft tracker that NASA and ESA have used to keep tabs on robotic spacecrafts exploring the Solar System.

Even before its formal dedication in 1980, the VLA had become an invaluable research tool. More than 5,000 astronomers from around the world have used the VLA for more than 14,000 different observing projects. The VLA has had a major impact on nearly every branch of astronomy, and the results of its research are abundant in the pages of scientific journals and textbooks. More than 500 Ph.D. degrees have been awarded on the basis of research done with the VLA.

Discoveries

Ice on Mercury

Mercury, the innermost planet of our Solar System, is less than half the size of the Earth but is twice as close to the Sun as we are. Parts of Mercury’s Moon-like, rocky surface are heated by the Sun to temperatures nearing 800 degrees Fahrenheit (425 degrees Celsius). This is not a world like ours, certainly.

However, in 1991, planetary scientists studied Mercury using a radar system consisting of NASA’s 70-meter (230-foot) dish antenna at Goldstone, California, equipped with a half-million-watt transmitter, and the VLA as the receiving system. The VLA was configured to map Mercury with detail down to 100 meters across.

The beam of 8.5-GHz microwaves sent from Goldstone bounced off Mercury and was collected at the VLA to produce a radar image of the planet. The researchers used the Goldstone-VLA radar system to look at the side of Mercury that was not photographed by Mariner 10 in the mid-1970s.

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