Telescopes and the Royal Observatory in Johannesburg with guest Des Fourie

Discover the universe with Thomas Budge as he unveils the marvels of stargazing, telescope crafting, and celestial events.

Thomas Budge, an amateur astronomer, shares his passion for stargazing from his farm. He discusses the evolution of telescopes, their construction, and the wonders of the night sky. Interviews with enthusiasts and astronomical phenomena add depth to his exploration.



August 1995 | Protea Ranch | Celestial Movement | Concepts of Time | the Royal Observatory, Johannesburg | the Innes Dome housing the 26" Grubb Refracting Telescope, built in England and brought to Johannesburg in the early 1920's | the History of Telescopes | Galileo's First Telescope | Amateur-built Telescopes | Newtonian Telescopes | Reflecting versus Refracting Telescopes | Optical Aberration | Grinding one's own Mirror | Interview with Des Fourie, Amateur Astronomer on Building a Telescope | History carried by Light in Time | Twelve Constellations of the Zodiac | Planetary Movement across the Zodiac along the Ecliptic | the Moon | Mars, Saturn and Jupiter | the Triple Crossing of the Orbital Plane of Saturn | Constellation of Scorpius and it's Mythology.

Video transcription

Hi, I'm Thom Budge and I'm here on my farm where I live in the Schurveberg, out near the Hartbeespoort Dam, away from the city, out looking for some of the species of birds and animals and insects that frequent the mountains. But you know, as an amateur astronomer, for me, the most exciting and rewarding thing is to see the night sky, and that's what we will be talking about in this series. People have studied and observed the night sky for thousands and thousands of years.

Sailors navigated their way across the oceans using the stars as their reference points. Whilst farmers waited for the rise of specific constellations before they would sow or reap their crops, the predictable motions of the earth and moon gave birth to our concepts of time in divisions of days, months, and years. But science has changed our lives dramatically since then. Isn't this technology amazing now? I spend hours in front of my computer in contact with other astronomers all over the planet. I even used this to connect to my telescope, and that allows me to view the night sky right here on my screen.

But you don't necessarily need this level of sophistication if you are going to enjoy the night sky.

Right here in the heart of Johannesburg, at the old observatory, there are some interesting telescopes. They are regularly used on public viewing evenings to give everyone a chance to probe the realms beyond our planet.

Inside the sturdy brick structure of the Innes Dome is a wonderful old telescope that was actually used by professional astronomers for 45 years. With this very instrument, many double stars were studied and catalogued. This is the Grubb telescope that was manufactured in England and brought out here in 1923-24. It is a very good example of a refracting telescope. Uh, the size of this is 26 and a half inches, and it's one of the last few remaining telescopes of this size in the world.

The very first telescope was built by Galileo in Italy in 1609. With it, he revolutionised astronomy. It was a refracting telescope, a particular kind of instrument that comprises a series of lenses that focus and project the image into the observer's eye.

Telescope design and manufacturing accuracy has progressed in leaps and bounds since Galileo's humble beginnings. I invited a number of very keen students to meet some enthusiastic amateur astronomers. These guys own some impressive equipment. The interesting fact is that many of these instruments were built by hand for a fraction of the cost of a commercially available equivalent. The students were so excited to see how the telescopes operated and to share some of the astronomers' construction experiences and design ideas. Although some modern telescopes have quite complex tracking devices to compensate for the Earth's rotation and a sophisticated computer interface for star location, the basic design principles are relatively simple.

It is this simplicity of design that allows almost anyone to build a telescope. I have seen some very good ones built for less than 500 Rand from odd bits and pieces lying around in the garage. Probably the most difficult component to make is the focusing mirror, which must be accurate enough to produce a crisp and undistorted image. Isaac Newton invented a telescope using a mirror to focus the image. Rather than a series of lenses, light rays falling on a parabolic surface, converged to a prime focal point.

A flat secondary mirror bends the focused rays through 90 degrees into the eyepiece.

Contrary to expectation, it is relatively easy to grind a parabolic curve into a thick slab of glass to make the primary mirror, a task I demonstrated to my young friends.

Was this the same kind of telescope that was used by Galileo?

No, the refracting telescope came first. Galileo's telescope was a refracting telescope, but the problem with the refracting telescope was that the objective lenses were difficult to make. And, when they were looking at the stars, those stars had like coloured doughnut bands of color around them, like doughnut around the stars, a thing we call aberration. And the way they tried to overcome that was to make the length of the tube longer and longer and longer. So refracting telescopes in order to get over the problems of aberration, became very long instruments.

And then Isaac Newton thought, no, hang on. There's got to be a different way of doing this. And he invented the reflecting telescope with a parabolic mirror at the bottom and light coming in, focusing to a focal point, and then having a mirror at 45 degrees to take the light back out again. So, it was a good number of years after the refracting telescope was made that the reflectors were then invented by Isaac Newton.

Why do you wanna make, um, a mirror instead of just using a lens to focus the light and just look at that?

Okay. To make a mirror is far cheaper and far easier because you just need one focusing surface. If you want to make what we call a re refracting telescope, that is a telescope that has lenses in it, it is so much more difficult to because here you've only got one surface that you need to get accurate. There you have different surfaces and different structures of lenses in order to focus the light properly. So refracting telescopes are much, much more difficult to make than a reflecting telescope. That's why the amateurs tend to go for reflecting telescopes rather than refracting ones.

Anyway, what we've got here are two pieces of glass, and we are going to turn one of these pieces of glass into a mirror. The other piece of glass is just used as a tool. Um, and at the end of the day, what happens is we end up throwing that piece of glass away.

Now, in order to get the shape that we need out of this mirror, I explained how carborundum particles of various grades are inserted between these slabs of glass. This with a little water, provides the necessary abrasive element, the random action of the two pieces of glass result in the correct configuration for a telescope mirror by the grinding action of the glass. Now as we do that, what's happening is it's grinding away part of the top piece of glass and rounding the edges of the bottom piece of glass.

And when you've ground a little bit, turn the whole thing around so that you get a nice even grind.

Then, turn it again. Now notice how that water is starting to go a little bit milky now. Mm-Hmm, what's happening there is the carborundum is breaking down and it's also taking off some of the surface of the glass itself.

Can you also use normal sandpaper instead of using the small particles of carbon?

Right. You can't really use a bit of sandpaper because if I took a piece of sandpaper and tried to use it in my hands, I'm not going to get that very, very accurate shape that I'm looking for. See, I want to grind this piece of glass away so that, that it's a little bit deeper in the middle and comes sloping up towards the edges. And the only way I can do that is by grinding this piece of glass on top of the other one, because as I move this piece of glass, I tend to put some more force on this one. So it grinds away and the edge of that glass grinds into this piece of glass. So it's not so much the grit, it's also the action of the piece of glass underneath the tool by moving one piece over the top of the other and then changing direction, constantly changing direction that allows me to get just that perfect shape that I'm looking for.

So I couldn't take a piece of sandpaper and just try and sand it. I'd never get the accurate shape.

Um, it's the, the glass on top. Is that gonna become your mirror now?

The piece of glass on the top is the mirror. The piece of glass at the bottom is going to be thrown away. That's what we call the tool. You see what's happening here is if I can just go through it again as I move this piece of glass, what happens is it tends to bend a little bit over the bottom piece of glass. So this sharp edge of the glass here, along with the grit, wears the top piece of glass away in a concave shape. But the bottom piece, all the edges will be rounded and it'll end up as a perfect match, but a convex mirror.

Now you can't use the convex mirror, but you can use the concave mirror.

Don't you have scratching of your lens here 'cause you're using such a half surface?

Yes. Right now there's a lot of scratching of the mirror. In fact, if you have a look at this mirror now, it's very, very rough indeed. But what I'm trying to do is I'm trying to very quickly take away the layers of glass to get down to the depth that I'm looking for. Once I get down to that depth, then I'll use fine powders, which won't scratch any more. They will take out the scratches. So I'm going to polish out the scratches that I've made with this particular size of grit.

How do you know you've finished, uh, the right depth? Yeah?

As you move this piece of glass, so you're grinding bits of it away. And in order to measure its accuracy, periodically what you do is you take it off of the tool, clean it nicely with a sponge, and then we use a gadget like this one. This is called a s spherometer, and by placing this gadget, it's a micrometer that has very, very accurate measurement, by placing this over your mirror, you can actually then see by setting the gauges just precisely how much glass you've ground away off of that part, the mirror itself.

Okay. How long would you have to carry on creating this thing?

Um, to make a mirror takes in the region of about 40 hours. People think that it is a very difficult task, but it's not really, you know, about 40 hours of hard work makes your mirror. And then I think there's a lot of effort in making the whole superstructure, the telescope frame and the mounting, and so on. But about 40 hours to get a good mirror.


Des Fourie is an amateur astronomer who despite his physical disadvantages, constructed his very own telescope.

Des what got you interested in astronomy?

Well, number one, the first thing is that I've been interested in astronomy for a long time, but what really got me actually involved after the series of operations, which left me in this state. I had lost most of the things that I could do and I had to have something to absorb me. Once again, astronomy is one of these things, which the deeper you go, the deeper you can still go.

Yes, you start off at a very elementary level, 'it's just fun making a mirror' for instance, then you used it and you begin to realise that there's more in the sky than you've ever imagined there was. So you begin to investigate the deeper aspects that you get onto things like variable stars, double stars, comet hunting. Yes, I mean the first time you see a meteor crossing your eyepiece, it is the most fabulous thing you've seen, isn't it?

Des, you set about building your own telescope, was it really difficult to do?

No, that's the beauty of it. It's not something that you have to have lots and lots of money to do. You don't have to have huge amounts of time. It might be thought that this is for some semi-paralysed character like myself who's got nothing better to do all day long, but that's not the case. It can be done with a minimum of time if you're prepared to just keep applying yourself.

All it needs is a certain amount of stick. Stick-at-it-ness. Yes, if you're prepared to give the attention and exercise patience because it is slow, it's not fast, but if you're prepared to do that, anybody can make the telescope.

So Des, what is the one thing that you benefited from?

It's therapeutic more than anything else. It gives my shoulders exercise, but what makes the difference for me is that I don't have to stand, yes, using this turntable, all I need to do is turn the mirror and of course the tool turns with, turns again also, and I sit still and I can just carry on for an hour at time without any problems at all.

And uh, about how long did it take you to get the mirror properly configured?

The six inch took me about 30 hours.

30 hours at making a mirror. Wouldn't it have been easier just to make it with a machine?

From the point of view of getting the gross measurement right?, probably a machine would be easier, but the machines have a problem that they introduce systematic errors because of their very regularity because they are so fine. So how shall I put it? Inelastic. You'll get errors being built up in mirror itself, whereas the human touch, because you're never doing two things the same way, exactly the same way, that enables you to wipe out those errors.

Each error compensates for the previous one, with a result, you probably have less trouble getting the right spherical surface than you would if you had a machine.


The settings sun marked the time the students had been waiting for their chance to view the night sky through a telescope. The sun is the closest star to planet earth, and as we waited for it to set below the horizon, we pondered the dimensions of the universe in awe. Some of the questions verging on science fiction.

But if you could travel about like, at the speed of light, we could go back in time, right?

Um, well you see what's happening is the light that's coming from the stars to us is carrying history with it. Take Jupiter. When we see Jupiter, we are seeing Jupiter, oh anything from 30 to 40 minutes ago. We are looking at the sun, eight and a half minutes ago. If the sun disappeared now, we wouldn't know about it for another eight and a half minutes. That's how far things are away from each other. So even if you could travel at the speed of light, you'd have to go, to get to the nearest stop, you'd have to travel for four and a half years to get there and other stars are hundreds of light-years away.


If you are lucky enough to own a pair of binoculars or a telescope, I'm sure you're keen to know what to look out for in the night sky. If you don't own any optical instrument, don't despair. Studying the night sky is still very rewarding. Now one of your first tasks should be to learn to recognise the 12 constellations of the zodiac. These are particularly important because the sun appears to move through them as the earth circles it every 12 months. The other eight planets in the solar system also move amongst the constellations of the zodiac of the nine planets.

Mercury orbits closest to the sun on the 28th of July, it was in superior conjunction a term used by astronomers, that really means that mercury was directly behind the sun and thus obscured from our vision. Since then, it has been moving rather rapidly eastwards against the starry backdrop further and further away from the sun.

It should be an interesting phenomenon to watch every night. On September the ninth, it will reach greatest eastern elongation, another astronomical term, which simply means that it will have reached its furthest distance from the sun in the evening sky, some 27 degrees. Mercury slides through the constellations of Leo and into Virgo. Look out for it above the western horizon, about half an hour after sunset, let's say around 6:20 PM. It should then be visible for another hour to an hour and a half.

Mars is in the constellation of Virgo and sets quite early in the evening around about seven eight o'clock. Jupiter is in Scorpio and sets after midnight around about 1 AM in the morning. Of course, let's not forget the moon. It's full moon on the 10th of August, last quarter on the 18th of August, and the new Moon on the 26th of August, that's when we see only the dark side of the moon.

The moon then moves into its first quarter phase on the 2nd of September. Saturn is also putting on a particularly rare and splendid performance this year. 15 years ago, the earth passed through the plane of Saturn's rings. Saturn's rings are tilted at quite a considerably steep angle to its orbital plane and it circles the sun once in nearly 30 years. This year and next, we are fortunate enough to witness not only one pass through Saturn's ring plane, but three the first occurred on the 21st of May.

It reoccurred on the 11th of August and will happen once more on the 11th of February next year. This phenomenon will not occur again for another 13 years. And a triple crossing like the one we're experiencing now will only happen again in the year 2038. As the earth crosses the plane of Saturn's rings, we observe the rings edge on. At this time we see them only as a bright line across the planet's face.

What is also interesting is that the sun also periodically crosses the plane of Saturn's rings before the 21st of May. The sun and the earth were on the same side of the plane and the rings were illuminated by the sun. After our crossing, we may see the shadowy side of Saturn's rings because the sun has not yet crossed the plane from the 11th of August, we again cross above the plane to the same side as the sun, and we see the rings illuminated once more on the 19th of November.

Whilst we are still above the plane, the sun crosses below the plane and the rings once again present their shadowy side to us. Finally, on the 11th of February, when we again cross the plane of the rings, we will be on the same side as the sun and we will see the rings fully illuminated for years to come. The triple crossing is very interesting to watch.

If you don't have access to a telescope of your own, you may wish to contact your local astronomical society, and I'm sure that those amateur enthusiasts would be delighted to show you Saturn's rings. To fully appreciate this phenomenon, you should try to observe Saturn several times before and after each crossing. We can also count ourselves very lucky because Saturn is well positioned in the evening sky. It is in the constellation of Aquarius close to Pisces and rises around about seven to eight in the evening and it's visible throughout the night.

Although Mercury and Saturn will capture most of our interest this month, the dominant constellation remains Scorpio. The scorpion is easy to locate and was the creature that was sent by Gaia, the goddess of the earth to mortally wound Orion the great hunter who was determined to kill all of Earth's animals. As Orion sets, fatally wounded, so the scorpion rises to dominate the night sky. But Orion is miraculously resurrected. He rises to take control again just as the scorpion loses its power over the hunter and sets below the horizon.

This drama repeats night after night as it has for centuries.

At the heart of the scorpion is the star Antares, a red super giant, 400 times the diameter of the sun. It has a blue orbiting companion star, which orbits Antares once every 900 years. The scorpion's sting lies close to the dense part of the Milky Way. Scanning this part of the night sky with a pair of binoculars is a most rewarding experience.

Until next time, wishing you clear skies.

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