[Our newest writer hails from Lancashire (England), where she is also brand new faculty at a local College. Though she will primarily be covering science fiction in film and print, she is also a bit of a scientist, as you'll see from this most intriguing new article. If only Analog could get pieces this readable…]

By Jessica Holmes

On clear nights, I like to bundle myself up in as many blankets as I can find, wheel my way over to the park, and sit clutching a flask of tea as I peer down the sight of my fold-up telescope, gazing at the stars. It’s been a ritual of mine for as long as I can remember, ever since I got my very first telescope and charged up the hill to get a better look at the moon. I recall being tremendously disappointed until my mother pointed out I hadn’t taken the lens cap off.

When I managed to use it properly, it opened a window to worlds beyond worlds, and I’ve been hooked ever since. I’m no astronomer by any means, more of an enthusiastic amateur. If I'm lucky, I may get a nice look at the Galilean Moons, but I often find myself wishing I could see so much more, wondering if somewhere out there, there's someone peering back, too far away to see. Then again, that might be the starry-eyed romantic side of me, having grown up with my nose firmly buried in any book that could take me to another world. Well, just this week, the stars came a little bit closer with the opening of a new telescope.

This is the Arecibo Observatory, and it's the largest radio telescope built to date:

Image courtesy of NAIC

The Call Of The Night

But what is a radio telescope? How can we observe space through radio? Does Jupiter sing? Are the bodies of the solar system harmonising in a heavenly chorus?

Well, that's not far off the mark. If you have the right equipment, you can even listen to Jupiter’s emissions yourself! You’ll need a shortwave radio (Jupiter radiates strongest at 22Mhz), and you’ll have to build yourself a large dipole antenna. What you'll hear is an eerie, aggressive static, a lot like waves crashing on the beach. These are the radio emissions produced by charged particles racing through Jupiter’s magnetic field.

The visible portion of the electromagnetic spectrum conveys but a tiny slice of all the information that can be observed in our universe. Above the range of our sight lies the realm of ionising radiation: the extreme ultraviolet, hard and soft x-rays (yes, just like the ones doctors use in hospitals) and deadly gamma rays. Below the range of frequencies we can see is the infrared, and lower in frequency still is the realm of microwaves and radio waves. There are objects in the sky which are utterly undetectable through modern optical telescopes, but the Observatory may detect its invisible radio emanations. Take the recently discovered 'quasi-stellar objects' for example. These are colossal structures located out in the furthest reaches of space, their light so red-shifted that it’s only recently that we’ve actually been able to see one with an optical telescope. How did we know they’re out there? Because they’re screaming at us — in the radio spectrum.

Artist’s impression of a quasar. Image courtesy of JPL.

Radar And Pylons And Dishes, Oh My!

Designed by Professor Gordon and engineered by T. C. Kavanagh, the observatory, which has been in construction since mid-1960, was dedicated on the first of this month and cost a hefty $9.3 million to build. For those of us on my side of the pond, that's £ 3, 323, 995 13s 9½d, if my calculations are correct.

So, what shiny toys did this money buy? More than I ever got for Christmas as a child, that's for sure. Nestled in a natural karst sinkhole south of the Puerto Rican town of Arecibo, the colossal wire-mesh dish, suspended by three pylons of which the tallest is 111m (365 ft), currently operates at frequencies between 300 Mhz and 10 GHz. This is much higher in frequency than any radio station you or I might tune in to, as the FM radio band caps off at 108 MHz. The dish is spherical in contour, and so focuses along a line rather than a fixed point as a parabolic reflector does. While this requires a complex line-feed system in order to carry out observations, the trade-off is that it enables repositioning of the receiver in order to view different parts of the night sky. This is because a spherical mirror's error is the same in every direction, whereas as with a parabolic reflector moving the receiver away from the focal point would produce uneven astigmatism.

This receiver is suspended 46 m (150 ft) over the reflector on a 900-ton platform, which sits on a rotating track, the 93m (305 ft) azimuth arm, enabling the telescope to observe the heavens in a forty-degree cone of visibility about the local zenith (an imaginary point in the sky directly above the observatory). This unique suspension system was devised by Helias Doundoulakis. The observatory is also equipped with a 430 MHz radar, which has been in operation since October last year, and is capable of taking measurements in Earth's ionosphere (the ionised part of our upper atmosphere), and radar astronomy, in which microwaves are bounced off distant objects so astronomers can analyse the reflections. There is a catch, however: the round-trip of light to objects beyond Saturn is longer than the telescope can actually track them, so it isn’t possible to make radar observations of more distant objects.

The observatory under construction, a year and a day ago. Image courtesy of NAIC

One Eye On The Future

How, precisely, does it work? Let us say, for example, that the telescope was making an observation of Jupiter. As the radio waves from Jupiter reach Earth, they are collected in the dish, which is curved to focus the signal into the receiver, which moves to track the planet's movement through the observatory's cone of visibility. The data are then recorded, and collected by astronomers for interpretation.

With this, it is hoped that the Observatory can give astronomers a greater understanding of our celestial neighbours, with some of the finest observations yet achieved.

Closer to home, it is hoped that the Observatory will give us a greater understanding of our own world. Professor Gordon's initial intention of the Observatory was to study Earth's ionosphere. The dish can take measurements of radio waves in this area, and the on-site radar, as mentioned above, can send and receive signals into and out of the ionosphere. With these, it will be possible to measure electron density, ion and electron temperatures, ion composition and plasma velocity with the new equipment, through a technique of Professor Gordon's devising in which a radar beam is sent into the ionosphere, which then becomes scattered, and this scattering is recorded by the instrument, and can then be interpreted.

In time, the Observatory will be able to peer further and further into the reaches of space, making detailed observations of our solar system and beyond. At any rate, I'm excited to see what secrets of the stars the Observatory may unfold, and eagerly await the many thrilling discoveries that are sure to come. Oh, and should any astronomers happen to hear any outer-space radio shows, be sure to tell me the frequency. I’d love to tune in some time.

Further reading:

For anyone interested in carrying out some amateur radio astronomy, you can contact NASA, who will be happy to share instructional resources for just that.

And if you’re a scientist and you’d like to make use of the Observatory, you can get in contact with the committee to submit your proposal.