Parkes Radio Telescope Questions and Answers

Can you give me a one-page description of the Parkes Radio Telescope first?

Yes. In a remote paddock 20 km north of Parkes, NSW, is a giant 64-metre dish. The strange metallic structure is a telescope - astronomers use it to study the heavens!

Astronomers are curious about things in our galaxy, and beyond our galaxy out in the universe. To astronomers the world is one big workshop, and telescopes are its tools. This dish - together with its electronic systems - is one of those tools, but it is sensitive to radio energy not light. It is used to measure radio properties of specific celestial phenomena, by a succession of visiting astronomers from around the world, in experiments that last typically several days.

Astronomers have known for years that cosmic radio energy is created, as naturally as heat and light, by such things as quasars, galaxies, molecular clouds, supernovae and pulsars. This radio energy shines, weakly, on every square metre of the Earth's surface. The ground underneath the dish does not get its "fair share" of radio energy: it is intercepted by the reflecting metal surface, the shape of which - a parabola - concentrates the radio waves into a receiver at the focus 27 metres above. CSIRO's radio telescope at Parkes is ten thousand times more sensitive than when first commissioned in 1961, a result of the continuous development of increasingly sensitive and versatile receivers.

In the spirit of international cooperation, this dish is occasionally used to help JPL/ NASA with collection of data from its spacecraft exploring the planets. Famous for its role in relaying Apollo 11 telemetry and television pictures from the Moon on 21st July, 1969 - the movie "The Dish" was loosely based on that involvement - it has more recently assisted with Voyager 2 at Uranus (January, 1986) and Neptune (August, 1989), Giotto at Comet Halley (March, 1986) and Galileo at Jupiter (most of 1997).

What is that big dish?

The Parkes radio telescope is a gigantic measuring instrument, used to examine a wide range of radio energies from our galaxy and other parts of the universe.

Objects such as pulsars, galaxies and quasars broadcast enormous quantities of radio energy into space.

Who uses it?

Radio astronomers from all over the world apply to use our radio telescope, hoping to obtain specific answers to specific questions about specific astronomical objects.

In 1996, altogether 262 astronomers came from 15 Australian institutions, and 21 overseas countries.

Does Parkes have anything to do with the optical telescopes at Siding Spring near Coonabarabran?

No, we are separate institutions working independently from day to day, but we're like co-authors of an astronomical story, each using different technology yet similar vocabularies to supply different paragraphs of interest.

Light cannot travel through the dust in our galaxy - but radio waves do, so most information about the centre of our galaxy comes from radio astronomy; the vast majority of pulsars are detectable only in radio, but when a pulsar recently penetrated the atmosphere of its companion star many optical, ultra-violet and x-ray observatories observed this event in their own special ways too.

How does it work?

The complex structure of the dish you see is designed to get as many radio waves as possible from a designated part of the sky, shining, for as long as possible, on a sensitive little wire at the focus - the rest are just details of innovative engineering, computing, and world-class astrophysics!

Our system amplifies very weak cosmic signals over a million million times.

Do we see or listen to anything?

No, radio astronomers make a series of electronic measurements about the radio properties of an object of interest to them, and the data are reported as a graph, map, or list of informative numbers on a computer screen.

A mixture of radio waves can be sorted into a graph of strength~wavelength; a radio spectrum.

Do we ever get anything strange?

Yes, all the time - but nothing that a competent astronomer wouldn't think was just the temporary effects of random noise or man-made interference.

A microwave oven made a nuisance of itself recently, when visiting astronomers ignored our warning note on its door and used it during their observations.

Could we miss something important?

Yes, but science rests on the repeatability of data, so a "mysterious" signal would be noticed again if it were real, and perhaps be suitable for study at a later date (depending on the curiosity and priorities of the astronomer).

A stray signal from an extra-terrestrial civilisation would have to last long enough to be observed many times before it was believed (we haven't even come close yet).

How do radio astronomers interpret radio waves?

Different substances produce different radio waves which are distorted by the physical conditions they encounter; the astronomers' measurements are highly relevant to the question asked, so they are fairly easily able to interpret their data in the light of their existing knowledge.

A radio spectrum from the atomic hydrogen in a spiral galaxy quickly reveals that galaxy's speed and rotation.

Has it ever discovered anything?

Yes, we've often made the headlines, however data belongs to the visiting observers and their results are published the world's astronomical journals.

The first precise position of a quasar, 3C273; the existence galactic magnetic fields; comprehensive catalogues of the radio sky at different frequencies.

What is "noise"?

Noise disguises a signal; its the electronic equivalent of little extra puffs of smoke that accidentally get out from under the blanket in a smoke signal.

When collecting trillionths of a watt of signal from space, any heat energy in the receiver pre-amplifier circuits will be a significant source of noise unless proper precautions are taken.

How far can it "see"?

That's a bit like asking how far away can one hear something?- in which case the answer would depend on the loudness of the noise and the sensitivity of one's ears.

We found the very powerful quasar PKS 2000-330 at a record distance of 20,000 million light years in 1982, and in 1993 we detected the least luminous pulsar known only 150 light years away.

How does a radio telescope started in 1961 stay up-to-date?

Parkes is an electronic telescope; the advances in electronics and computers of the last few decades make it a better telescope now than it ever was!

Our new 13-beam receiver, designed for the HI Parkes All Sky Survey, and new multi-receiver focus cabin make us again the best single dish radio telescope in the world.

What did we do before computers?

Earlier astronomers had no option but to dissect the big questions into smaller, manageable portions that could be answered with the technology that was available at the time.

To study just one galaxy in an experiment would now be rare; now thousands of them would be studied further and fainter than ever before in an attempt, say, to measure expansion of the universe.

How many staff here?

About 20 staff keep the place running administratively and technically like a "scientific fast-food joint" for astronomers who "come, get what they want, and go".

Three of us live on-site, and will fix the telescope any time of the night if things go wrong.

Does the radio telescope move?

Yes, the dish moves slowly but surely as it follows a specific object, such as a galaxy, to compensate for the Earth's rotation. Other times it moves "in a hurry" towards the next object for study.

At its fastest rate, the dish takes 15 minutes to do a full circle, and 5 minutes to go from vertical to almost touching the ground.

Why do we sometimes prefer to use the diesel generator?

Sometimes it is important not to lose seconds of observing time. We are confident that the generator will not fail unexpectedly.

Where safety is at stake, the generator is preferred.

What powers the telescope?

Driving four 15-hp motors, local council electricity is filtered through an un-interruptible system which, in the event of failure, uses forty car batteries to preserve computer data until the diesel generator fires up automatically.

For the duration of the moon-walks the generator was our preferred supply of electricity.

Who decides where the telescope points?

In an experiment, astronomers will move the telescope towards the next object on their list when they decide that the data is good enough for a reliable answer. The experiments scheduled during a four-month observing period reflect the decisions of our time-allocation committee which previously sifted though the various applications and decided which experiments would produce the best science. Long-term initiatives requiring major changes to the telescope are proposed by far-sighted astronomers, and may be endorsed by an international Steering Committee

The molecular clouds in star-forming regions may need several hours of observation; the intense maser emissions from OH/IR stars need only several minutes; the HI Parkes All Sky Survey is a major initiative that will need 5 years to complete while sharing time on the telescope with other projects.

Who owns it?

We do; it's funded by Australian taxpayers and is a part of CSIRO's science.

CSIRO has many Divisions, and our Australia Telescope National Facility is just one of them.

Do astronomers pay to use the telescope?

No; astronomical observatories in the world exist to produce knowledge, not profit, although it is normal to charge for meals and accommodation. On the other hand, Parkes has gained prestige for Australia and money for itself as it is sometimes persuaded to turn aside from radio astronomy and track a spacecraft.

NASA paid us $2.4 million to track Galileo at Jupiter 10 hours a day in 1997.

Does astronomy do anything useful for the world?

Yes, but be patient.

The upward-and-outward curiosity of astronomy gave us timekeeping and ultimately the ability to navigate exactly around the world; it provided signal processing techniques in engineering, geology and medicine; it discovered the hole in the ozone layer and alerts us to the jeopardy of future impact from asteroids; and, perhaps most importantly, this curiosity supplies us all with a better understanding of our one-and-only, very precious and very fragile "spaceship Earth".