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In 1995, the South African Broadcasting Corporation (SABC-3) commissioned this astronomy television series, in which Thomas Budge visited key astronomical sites, interviewed many prominent astronomers, and taught the television audience how to get the most from their viewing the night sky.

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Outline

The Universe our Eyes cannot See | Refraction of Light | Colours of the Rainbow | Visible Light | The Electromagnetic Spectrum | X-rays | Radio Transmission | Infrared | Ultraviolet | Anthony Voorveld | Refraction, the Bending of Light | All Bands of Energy in the Electromagnetic Spectrum can Refract | Microwave Refraction | Polarisation of Light | Polarisation of Radio Waves | Focussing Light | Focussing Radio Waves | Hartebeeshoek Radio Astronomical Observatory (HartRAO) | Cassegrain Reflector | The Principle Workings of a Light Telescope | Dr George Nicholson | The Principle Workings of a Radio Telescope | The Universe in Different Wavelengths | Very-long-baseline Interferometry (VLBI) | Justin Jonas | Rhodes University | Radio Map of the Southern Skies | Comet in Visible Light | Radio Image of Comet | Centaurus A in Visible Light | Radio Image of Centaurus A | Radio Map of the Milky Way Galaxy | Observing Mercury | Venus | Mars | Jupiter | Saturn | Transit through Saturn's Ring Plane | Comet Hale-Bopp | Swiss Astronomers, Didier Queloz and Michel Mayor | Discovery of Planet around 51 Pegasi | Book Recommendations.

Video transcription

In this episode of Out of This World, we take a look at the invisible universe.

Now that sounds like a contradiction in terms, but modern technology has allowed us to examine space with instruments that looked quite different from a conventional telescope. 400 years ago, our knowledge was very limited, but because of these technological advances, we have greatly expanded our understanding of the universe. Way back in 1610, in Padua, in Italy, Galileo turned the first telescope Skywards to reveal details of Venus, Jupiter, the moon, and the Milky Way, that we had never known existed.

Astronomy had been revolutionised.

Sir Isaac Newton's invention of the reflecting telescope, using a parabolic mirror instead of complex lenses, made further significant contributions to our understanding of space. The race was on to build larger, more precise instruments to probe even deeper into the universe to reveal as much detail as possible. Unfortunately, as telescope designs were refined, natural limits of our earthly home had a limiting effect on just how much we could see.

The thick, transparent blanket of our atmosphere disperses light, scattering its rays in all directions. Wind, heat, and water vapour all disturb the atmosphere, adversely affecting the details our terrestrial telescopes can resolve. However, an interesting discovery made by Sir Isaac Newton, has resulted in a very specialised branch of astronomy, the radio telescope.

Newton discovered that a small beam of sunlight falling on a glass prism split it into a spectrum of colours, ranging from red through orange, yellow, green, blue, indigo, and violet. These are the same colours we see in the rainbow when the sun's rays refract through tiny water particles after the rain. Herschel performed some experiments on these colours by measuring the temperature within each colour band. Quite by accident, he found that the temperature increased dramatically just beyond the edge of the red, where there was apparently no colour at all. Herschel had discovered infrared. More importantly and quite unbeknown to him, he had discovered the electromagnetic spectrum.

Light is that tiny part of a much wider spectrum that is visible to the human eye. In fact, the spectrum extends considerably beyond the visible light in both directions, and includes x-ray, radiation, radio transmission, infrared, and ultraviolet. Our eyes are nothing more than specific receivers that are tuned to specific wavelengths of light.

Just like a radio receiver can be tuned to other wavelengths where we can listen to the broadcasting stations quite independently, science has utilised the electromagnetic spectrum in many beneficial ways. The very short wavelengths of x-ray penetrate tissue, but not bone, allowing doctors to see into the human frame without surgery.

Although visible light struggles to penetrate cloud and smoke, infrared radiation has no trouble in penetrating these substances. The human body radiates an abundance of infrared radiation. Using specialised camera equipment tuned to these wavelengths, rescue operations are simplified, animals can be located in the bush at night, and military manoeuvres can be executed in conditions where our eyes are useless. Parts of the electromagnetic radiation spectrum are in commonplace use.

In our homes, our radio and television broadcasts are carried on longer wavelengths in the spectrum. Our security detectors use infrared wavelengths, and the TV remote control transmits its instructions to your TV set using infrared wavelengths. Interestingly, the physical properties of light apply equally well to any other wavelength along the spectrum.

 

I went along to visit Anthony Voorveld, a physics lecturer at Wits University, and a keen amateur astronomer, to discuss these common properties.

He demonstrated the similarities between light and radio by means of some quite elementary experiments. Just as light can be focused with a parabolic mirror, so can other wavelengths. Using an old mirror from a military search light, we demonstrated the deadly effects of focusing infrared rays of the sun.

There we are, we're cutting the can through quite nicely.

So Tony, is it the infrared that is doing the damage to the tin?

Yes. The part that is doing the cutting, that is doing all burning and so on, is the infrared part of the spectrum, and that's the part of course that you feel on your skin.

This is identical to the way a telescope focuses light off of its mirror.

What I'd like to do is now to show you the relationship between light and radio waves, and the simple experiment that we are going to perform. Now, we're going to pass light from a laser into the prism. This will be refracted, okay, in other words, bent. And we'll place this on the card. Our laser beam shines in there. There it is. It's just been bent by the bit of glass. You see that simple piece of apparatus bends the light over, and there it is. We bent light that's part of the electromagnetic spectrum we call light.

A light ray entering a glass prism is bent or refracted along its path. Remarkably, and perhaps quite contrary to expectation, radio waves behave in precisely the same manner. Tony demonstrated these properties with a small microwave transmitter and receiver pair.

So the transmitter sending a signal out here, missing the receiver totally, and the receiver's looking somewhere else. Okay, there we are, let's bring this prism in. Somewhat different to the one you were looking at just now inside.

Yes, it is much larger.

Well, yes, because it's proportional to the wavelength that we're working on. You see, let's bring it in. There. You can see it obviously see the wave signals being passed in there, refracted, bent as it was with the light there, it goes into the receiver.

You may have noticed how the light from your torch is reflected off a shiny surface. Radio waves, that are part of the same spectrum, behave in exactly the same way.

Here we have an aluminum piece, a piece of aluminum as a reflector. It doesn't have to be highly polished because we are not dealing with light any more. Let's see what happens. You can see on the oscilloscope. Can you see on the scope there? You can see the wave there quite nicely. If I take it away, it disappears. Let's bring it back in again. There's the wave.

Polarised sunglasses cut, the sun's glare, allowing only the light rays that are aligned in a certain direction to pass through them.

In exactly the same way, a polarised lens or a polarised piece of glass. If you simply looked at it under a very powerful microscope, you would see thousands of parallel lines, very much the same as this, but because our wavelengths are so much longer, we can do this with a much wider series of grating, as you can see here. Now, let's try this. We'll put the transmitter there, and the receiver there, like that. Now incidentally, I must just stress here that the signal coming out of this transmitter is horizontally polarised, right? The waves are coming out in a horizontal manner. There are no vertical waves coming out of here. Now, if I put the grating that way, the signal still appears on the screen. No change. Now let's place the bars vertically. You can see on the oscilloscope that it's, we can still see through there, but the waves don't. They get blocked, but there it is. Let's try that again. Let's bring that over. Signal passes through polarisation.

Returning to our army searchlight reflector, Tony demonstrated how radio waves can be focused using the same piece of equipment.

We've got our transmitter set up just a little way out on the other side of the room. Let's see. Very weak signal there. Let's move it in. Yes, there it is. It's about that point over there. When you move it away, it disappears, and when you move it in, it would disappear. Now let's move to the side. Gone.

 

If then, as we've just seen, all the components of the electromagnetic radiation spectrum behave in the same manner, couldn't we examine some of the other waves emanating from space to see the invisible universe?

Nestled in the Magaliesburg hills, to shield it from stray radio signals from Johannesburg and Pretoria, lies the enormous radio telescope at the Hartebeeshoek Observatory, accompanied by Protech students. I visited the facility and spoke with its director, Dr George Nicholson.

This facility was built in 1961, and was originally used up until 1975, to track American deep space probes, the unmanned probes to the moon and planets. NASA withdrew from the site in 1975, and since then we've used it exclusively as an astronomical observatory. It's a national research facility, that's available to astronomers in the universities, the international community, and we collaborate in quite a wide range of international projects. And the telescope itself is 26 meters in diameter. The moving part of the structure weighs about 200 tons, but it's still a precision instrument. We can point it with considerable accuracy. It's essentially a parabolic reflector, which picks up radio signals, focuses them up towards the apex of the telescope where they're intercepted by a cassegrain reflector, and then focused down into the large conical structure.

Dwarfed under the massive dish of the radio telescope, I showed my ego companions the principle operation of my own telescope.

Okay, so it's the sun's light that is reflecting off of the moon, and then parallel rays of light are coming down into the aperture of the telescope here, all the way down to the bottom of the telescope, and lying in the bottom of this tube is a curved mirror. It's a parabolic mirror, and that mirror then takes these parallel lines of light, bends them and focuses them, but it focuses them back out. So, to catch those focused light rays right at the top of the telescope in the middle of the aperture, sits another little mirror, and then these light rays coming up would bounce off of that mirror, and focus down through this hole in the bottom, and out into the eyepiece.

Parallel rays of light into the aperture fall onto the primary mirror. There they are focused onto the secondary mirror that reflects them into the eyepiece because light and radio waves follow the same laws of physics. The operation of my telescope is considerably similar to that of Hartebeeshoek. Instead of parallel rays of light striking the primary mirror, parallel rays of radio waves strike the dish. It is shaped in the same way as the mirror in my telescope, to bend and reflect the focused waves onto the secondary reflector, which sends them down into the sensitive radio receivers.

This particular telescope has a control computer, and there are two motors in this telescope, one that moves the telescope this way, and another one that moves the telescope that way, and via this computer, it then keeps tracking that particular object up there. So, the whole idea of this is that as the earth is rotating on its access, giving us day and night, what's happening here is the telescope is being driven exactly in the opposite direction, and at exactly the same rate as the earth is moving, so that whatever the object is that we're looking at, stays very fixed in our sites.

So can one actually attach a camera to this and take photos of what you're looking at?

This whole eyepiece where we're looking at the lens itself, that whole attachment comes off, and another device gets screwed onto there, and you can put a camera on, so that you can take normal photographs of the sky. And if you want to really take long photographs of the sky, to do a time exposure, then you need these tracking motors to make sure that that object doesn't move, because if it moved, it would blur on your film.

Dr. Nicholson, this is the main control room for the telescope. Can you tell us a little bit more about it?

Yes, certainly. Basically, this is the control panel that operates generally under computer control, but you can operate the telescope manually with these hand controls over here, if necessary. These displays over here, indicate where the telescope is pointing in an east-west direction. The hour angle and declination is the north-south angle of the telescope. You can see it's constantly moving here, because it's tracking a fixed point in space. Over here, we have a new control computer for the telescope, which is under development, and further along, we have other instruments. We have an instrument for measuring the wind velocity, for example, so that we can see if we have very high winds, and it's then necessary to drive the telescope up to the Zenith position.

Student: Doctor, is the telescope focusing on one object?

Yes, that's an interesting question. The at the moment we are measuring one particular object. The observations we are making at the moment are to measure a whole collection of different objects over the next 24 hours.

Essentially what we do, we have a computer file that's a list of positions of all the objects we are going to observe for say the next 20 hours. It'll give us the position on the sky, like the latitude and longitude of a place on the earth, and that allows us to, control the position of the telescope. So the computer tells a telescope where it should be pointing.

Student: Does the telescope itself focus on an object, or is it done manually?

Student: Doctor, the instruments behind you. What are they used for?

These are the focus and tilt controls for the telescope. Just as you have to focus a pair of binoculars or a camera, we have to focus the telescope. Well, the equipment we have over here is used essentially for just monitoring the signals that come down from the telescope. You can see they're two chart recorders over here. The chart recorder over on the left there is monitoring the measurements that have been made by the telescope today, and you can see the squiggly lines on that every time it does measurements on a particular object. You can see a change in the level of the recorder.

Student: So then why is it so important to measure the radiation of other subjects in space?

Well, if we want to understand the physics of the objects in the universe, we have to study them at all different wavelengths. It's not just enough to know what the visible light is like from these objects. We actually have to know what the radio waves are. Sometimes they're objects that only emit radio waves and don't emit the visible light. This equipment over here is used for setting the frequencies of the receivers, and as we move across the control room over here, we've got the control computers that are used for controlling the telescope recording data from the telescope. And coming over to this side of the control room, we've got what we call the VLBI equipment. This is our telescope over here. This is one in West Germany. This is one in North America, one in Brazil, and one in Chile. We use VLBI to measure continental drift. We can measure the individual distances between pairs of telescopes on the earth's surface with an accuracy of about one centimetre. The continents are drifting apart at rates of about 3 - 10 centimetres per annum. So over a period of years, we can very easily measure how fast the continents are moving away from, or towards Africa.

Dr. Nicholson, what has been the most significant program that you've run from this facility?

Well, it's hard to say what the most significant program is, but perhaps one of the major programs that's been in progress for approximately the past 10 years, even a bit more than 10 years, has been a radio map of the whole of the southern sky. This has been carried out by a group of various people at Rhodes University. Most of the work recently has done been done by Justin Jonas, and they've produced the most detailed radio map at the wavelength of 13 centimetres, of the southern radio sky. And this is being used extensively by scientists overseas. For example, the group studying the cosmic microwave background radiation use this map to see what the foreground radiation, from our own Milky Way, is like.

So looking through a telescope at an icy comet speeding through our solar system, we see it's white coma blown away by the solar wind. Examining it in another wavelength, here in infrared, it's nucleus is clearly visible. Radio pictures of Jupiter and Saturn reveal different details from the ones we have grown accustomed to. Much further afield lies Centurus A, a galaxy visible through a conventional telescope. What we see in the visible spectrum pales into insignificance when we compare this with the enormous jets we see in the radio bandwidth.

The Milky Way, our home galaxy, when seen through a conventional telescope, reveals millions of stars. However, it is only in the near infrared that we get to see its central nucleus. As we map the same structures in different wavelengths, different details emerge. The radio maps reveal enormous protrusions extending far into space. At Rhodes University in Grahamstown, Justin Jonas and his colleagues performed a systematic survey of the Milky Way over the last decade. Using the facilities at Hartebeeshoek, they've produced a sky map that is internationally acclaimed, showing details we can't see with our eyes. Observing emissions from space using the entire spectrum has brought us a long, long way in the 350 years since Galileo.

 

Welcome to Sky Watch that part of the program where I tell you what to look out for in the night sky.

I hope you're enjoying the series, and if you require any further information, you can contact me through your local planetarium or email me at the address displayed on the screen.

There is so much of interest right now, making it very difficult for me to decide where to begin. So let's take a look at the planets.

Mercury is the closest to the sun, and as such, travels around it much faster than any of the other planets in the solar system. For us observers in the south, Mercury's present morning apparition is most favourable this year. Watch it gain altitude morning after morning and the eastern sky. The best time to see it, is half an hour before sunrise. Between the 12th and the 17th of February, it'll remain at its greatest altitude, 18 degrees above the horizon, before dipping back down towards the sun. We will lose sight of it again around the middle of March.

Venus is the second major planet from the sun, and is one of the terrestrial planets. Venus supports a dense atmosphere because its orbit lies within ours. It can never stray further than 47 degrees from the sun. Being such a bright object, it is well recognised as either the morning, or the evening star. Currently brilliant in the western sky, Venus is visible for several hours after sunset. On the 2nd of February, it passes only one degree south of Saturn.

Mars, the red planet, so known for its reddish colour which can be seen with the naked eye, is not presently a good object to observe as it lies too close to the sun.

Jupiter is the giant of the solar system and is large enough to swallow up 1,317 Earth-sized objects. It is not visible at this time as it disappeared behind the sun for a while, and has just made its reappearance in the morning skies before dawn.

Saturn is rather fainter in the southwestern sky, and is coming out of the end of its apparition, when it disappeared behind the sun.

On the 11th and 12th of February, earth travels through Saturn's ring plane giving us the rare opportunity of seeing its rings edge on, a phenomenon we won't see for another 15 years or so.

Recently I spoke of the newly discovered comet Hale-Bopp. Speculation placed its nucleus at the size of Southern Africa. Amateur and professional astronomers alike have keenly observed its movement through the solar system, still beyond Jupiter's orbit. It has already appeared to have formed a coma, which is the fuzzy cloud of gas that melts off the surface of its icy nucleus. The Hubble Space telescope recorded images of this unusual member of the solar system, and revealed some remarkable facts. A massive jet is seen to emanate from the comet's spinning nucleus and swirls out in an anti-clockwise direction from it. Furthermore, a large bright fragment is clearly seen to drift some 110 kilometres from the nucleus, possibly having broken off and flung away by the centrifugal force. The Hubble Space telescope will be used to keep constant vigil on Hale-Bopp to see if it is truly a giant comet, or just an average one that has a short-lived supply of very volatile components.

In October last year, professional Swiss astronomers, Didier Queloz and Michel Mayor, operating the 1.9 meter telescope at the Haut Province Observatory in France, announced their discovery of a new planet. No, not a new planet in our solar system, but one orbiting around the distant star 51 Pegasi, some 42 light years from us. This star is almost an identical twin of the sun. Observations reveal that the newly discovered planet orbits 51 Pegasi at a distance of only 7 million kilometres, that is nearly eight times closer than Mercury is to the sun, yet it has a mass of nearly half that of Jupiter.

This discovery has put the theories of planet formation into turmoil. We have always believed that a solid body could not coalesce this close to a star. Is this assumption still correct, or did this giant planet form some distance away before drifting much closer in time? Further observations may give us a better insight.

If you are keen to learn about astronomy, I suggest you visit your local bookshop where you're bound to find many books on the subject. Up to date information is readily available in the monthly astronomy magazines, like Sky and Telescope and Astronomy. Books are quite another matter. Coffee table editions have beautiful photographs of distant galaxies, nebula and stars, but tend to lack the functionality, and the portability for use as a field guide.

Collins Field Guide is a pocket edition specifically designed for use in the field. Each star constellation is dealt with in turn, in the middle sections of the book. The accompanying full page star charts are printed white on black background, which is essential if you wish to retain your dark-adapted night vision. By far, the best book I have seen for a long while is David Levy's Sky Watching, which is comfortably sized for use in the field, and is rich in descriptive and photographic detail. The book is lavishly illustrated in colour and contains rich description of basic astronomy terms, concepts, and principles. It also covers each of the 88 constellations, with accompanying sky maps printed on dark background. This is a book that I can highly recommend.

Until next time. Wishing you clear night skies.



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