Cosmos

It was a happy surprise that the route to my next stop, Socorro New Mexico, would take me past the Very Large Array, a radio telescope with an antenna array that spans miles. Of course, as an electrical engineer and an astronomy buff, this was a must see. It was quite impressive viewed from the highway, but when I got to the visitors’ center, it turned out to be possibly the best technical tour I’ve ever taken.

A little background first: Radio telescopes are very sensitive radio receivers pointed toward the sky. Stars give off radio waves in addition to visible light. Radio waves travel through the gas and dust in space without being obstructed nearly as much as light, so radio telescopes are useful for “seeing” such things as the center of our own galaxy or the structure of distant galaxies and nebulae. Unlike optical telescopes, radio telescopes can be used day and night. The sharpness of the radio image that can be obtained improves as the diameter of the receiving antenna increases. There’s a physical limit to how large a single antenna can be, but with some fancy mathematics, the signals from multiple antennas can be combined to produce a single sharp image. That’s the principle of the Very Large Array; it has three lines of antennas that fan out with equal, 120 degree, angles between. Each line has nine antennas and there’s another one at the center where the lines come together for a total of 28. Each of the lines is actually a railroad track many miles long. The antennas are moved several times a year into different configurations. If they are moved as far apart as possible, the result is a very sharp image of a small part of the sky. If they are moved closer together, a lower resolution image of a larger portion of the sky is obtained. It takes a special purpose computer to combine the signals from all those antennas into a single image. This computer does only one thing but it does it very quickly. It performs 10 to the 16th multiplications of 32-bit binary numbers per second. That’s about 10 million times faster than a typical personal computer.

Okay, enough of the (possibly) boring science. Here’s what I saw from the road as I approached the array:

Okay, I thought, that’s kind of cool, though rather remote. I was afraid that was all I was going to see, plus a view of the train track for the antennas where it crosses the highway:

So I was thrilled when a couple miles down the road I came to a sign indicating a turn off to the visitor center. A few miles more confirmed that I’d reached the grounds:

Another few miles (it’s a big place) and I had reached the visitor center:

It looked a bit underwhelming, but there was this guy standing out front:

He was pointing a sci-fi looking device at people and cars in the parking lot. I struck up a short conversation and confirmed that his task was to look for cell phones that hadn’t been turned off. Signs on the way in warn you that cell phones can interfere with the signal the antennas are picking up.

Right inside the door of the visitor center you’re reminded that this facility was featured in the film “Contact” with Jodie Foster:

They also got Jodie Foster to do the narration for the introductory video in the visitor center, which is a neat tie-in. You’re also reminded that in the original COSMOS TV series, Carl Sagan can be seen climbing around on one of the antennas.

There really isn’t a lot in the visitor center; instead, there’s a self-guided walking tour of the outdoor facility which I found fascinating. Not only can you get up close with one of the antennas, but there are very informative signs and displays along the way explaining how they operate and what they can see. One of the first things you come across is an elaborate sun dial:

The ball in the center is the pointer, or gnomon. Where it casts its shadow indicates not only the hour of the day, but the month of the year. Each of the dark circles in the concrete is marked with an hour and a month (Actually two months, since the same markers are passed as the sun rises and falls from solstice to solstice). You can see that the markers are arranged in semicircles, each semicircle is for a different pair of months. One semicircle is on the near side of the pointer, which indicates that at the summer solstice, the sun is further north than the sundial. Also, you don’t see it in this picture, but there are markers placed way beyond the concrete pad for when the shadow is really long.

Soon after the sundial, you get your first good look at the antenna array:

and then you take a path that leads you up close to one of them:

until you’re right underneath:

The dish is 25 meters (82 feet) across. If you look closely, you can see the individual aluminum plates that make up the dish. They are each formed to follow a perfect parabola to within 0.5 millimeters. Here’s a shot past the base of one antenna out toward others in the array:

You can also see the railroad track used to move the antennas. This shot shows that the antennas themselves don’t have wheels:

Instead, a special train car can be moved under the antenna to jack it up and carry it to its new position. Each antenna position has its own siding off the main track, but instead of a switch and a gentle curve of track, the sidings cross the main track at right angles:

When the train car reaches the proper siding, the wheels are pulled up, turned 90 degrees, and set down on the other track. Here’s a picture of a train on the tracks; it’s not the one that moves the antennas, this one is used to maintain the rails:

After the close up view of the antenna, the tour takes you past the control room for the antenna array. I was standing outside in bright sunlight, looking through glass into the dim control room. I couldn’t see a thing so I pressed my face to the glass. About two feet away was a scientist staring back over the top of his computer screen. He grinned and waved at me; I waved back and slunk away.

Every so often, each of the antennas is pulled into a shelter for maintenance and upgrades. A short drive from the visitor center is the building where that work is done:

This shot gives the best sense of the size of the antenna by comparing to the SUV parked beside it. It’s about 100 feet from top to bottom.

From this inspiring place of science fact, my next stop, and next post, is a place that has inspired a lot of science fiction.