Big Art Dish Proposed

What is radio?

In daily use, “radio” generally names a means of communication. More fundamentally, radio is simply electromagnetic radiation at the low-frequency, long-wavelength end of the spectrum — the same physical phenomenon as visible light, only vibrating far more slowly and stretched across far larger waves.

Radio receivers intercept, filter, and amplify these electromagnetic signals by converting them into electrical signals. An analogy may be drawn to the retina and optic nerves of our eyes, which allow light energy to be detected and analyzed by the brain as neuro-electrical impulses. If radio is an extension of vision at lower frequencies, then what radio telescopes “see” is an extension of what we observe when we see light emitted from distant — or not so distant — bodies.

What is “seen” by radio telescopes?

A radio telescope — which BAD will be — is fundamentally the same as Newton’s optical reflecting telescope, save for two adjustments: (1) the scale and precision of the reflector are altered to accommodate radio frequencies, and (2) a radio detector is substituted for the eye.

The hugeness of radio waves compared to light waves has two main consequences for the design of the reflector. First, its surface need not be figured to the same optical precision (an optical mirror must be ground and polished like engineered glass to extreme tolerance). Second, the surface used to gather these larger wavelengths must itself be significantly larger. The largest planned optical instrument, the European Extremely Large Telescope (E-ELT), will have an aperture of forty meters; the name of the largest single-reflector radio telescope, built in Pingtang County, China, says it all: the Five-hundred-meter Aperture Spherical Telescope (FAST).

[Figure 1.1.3 — The Reflecting Telescope. From “An Account of a New Kind of Telescope, Invented by Mr. Isaac Newton,” London, 1672.]

Where do you look if you can’t see what’s out there?

Radio astronomy began by accident. Scanning the sky roughly in line with Sagittarius, Karl Jansky discovered the radio emissions emanating from the massive black hole at the center of our galaxy — and, though he would only later be recognized for it, ushered in an entirely new discipline.

Like Jansky’s accidental telescope, many contemporary radio telescopes use the rotation of the Earth, combined with very precisely directed antennae — often in groups or arrays — to scan the depths of the universe. Using Earth’s motion to direct an otherwise stationary telescope (radio, optical, or other) is known as drift scanning. This is what BAD will do from its location in the desert. The apparent motion of the stars around the north pole of the Earth’s axis, seen in a time-lapse image of the Karl G. Jansky Very Large Array (VLA), traces exactly this drift.

[Figures 1.3.2–1.3.3 — VLA time-lapse; drift-scanning diagram.]

Big Art Dish (BAD)

The BAD project has three main components: (1) a parabolic dish dug into the desert floor, (2) a receiving mechanism, and (3) a means of making its data freely available online. Its development requires establishing the technical requirements for the shape, structure, and surface of the dish; assembling the receiving equipment; testing materials and techniques; excavating and constructing the dish; and distributing and displaying its data — much of it through collaborative contribution.

As an artwork, BAD asks different questions than those posed by astronomers and cosmologists. It asks us to consider our own relationship to the cosmos, and to one another, through cultural knowledge production. Its construction and placement in the desert also prompt us to examine the technological, scientific, social, and governmental use of the environment in which it sits. It will: look out at the universe; provide information freely; be visible from above; and be visited on land.

[Figure 2.1.1 — The three main components of the BAD project.]

Number One Test, Big Art Dish (NOTBAD)

Plaster cast segments of a 1:5 scale model, showing the curvature of an f/D .4 dish with a 52 cm focal length.

Big Art Dish Model of Little Dish (BADMoLD) · January–February 2015

The BADMoLD was a full-scale, 130 cm (f/D .4) diameter dish cast in concrete. It was meant to further the understanding of the material qualities of dish construction and to serve as a test of the form.

Parabolic dish antennae are paraboloid surfaces. A parabola is the set of all points equidistant from the focus and the directrix, following a line parallel to the axis of symmetry. Measuring from the focus to the parabola, and from that point to the directrix, gives two segments of equal length — so the distance traveled by a wave reflected off the surface to the focus equals the distance it would travel straight through the surface to the directrix. Every part of an incoming wave front therefore arrives at the focus at the same instant: the simultaneous force of the wave is greatly increased by concentrating an entire wave front at a single point. This is the magic of parabolic reflectors.

[Figure 2.3.1 — Parabola geometry: focus, directrix, axis of symmetry.]

First Operational Antenna Model (FOAM) · Spring 2015

Following the failure of the BADMoLD, a new lightweight design for a dish of the same dimensions was made using foam-core, chipboard, and steel window screening. The Leech model includes a wave-guide feedhorn receiver built from a coffee can and coaxial cable — a “cantenna” — along with a high-gain, low-noise amplifier (LNA) and a Software-Directed Radio (SDR). Further changes to the design are being considered on the basis of other publicly available resources.

[Figures 2.3.x — NOTBAD plaster segments; the “cantenna” feedhorn.]

There is a small painting — Dürer’s St. Jerome in the Wilderness, in the National Gallery in London. On the front is the rather ordinary image of the early church father whose pursuit of knowledge, and of some sort of truth, drove him into the desert. On the reverse is a depiction of an astronomical event. Explanations vary as to what it is — perhaps a comet, perhaps a meteorite — but as a painting it has an almost Turner-esque atmospheric brushiness, a blaze of yellow and red crashing through from the upper right.

Why, for me, does an image — or, to be more precise, an object (it measures 23 cm by 17 cm and is about 2 or 3 cm thick) — hold the kind of sway this little five-hundred-year-old piece of wood does? It is as if, sandwiched between its two surfaces, in that 3 cm margin, is a three-hundred-year span of intellectual, aesthetic, and scientific change. In its anachronism it foresees a nineteenth-century sublimity, the kind that comes with going into the desert. But it also sees, in the technology of its own time, a condition that stands outside time.