Galileo in the Times of Modern Telescopes
Following is a small skit I wrote during my work with IUCAA SciPOP for the promotion of Thirty Metre Telescope in May 2019, on the occasion of Vigyan Samagam - India's first mega science exhibition.
Characters: Galileo Galilei, Optics kid, Telescope kid
Time duration: 35 - 40 minute
Words marked in Bold are to be emphasized in a dialogues.
Demonstrations and related diagrams are mentioned in Italics.
Good morning, everyone!
We welcome you all to India's first mega science exhibition, Vigyan Samagam.
We, the outreach team of Thirty Metre Telescope, that is TMT are here to share some of the fun activities with optics and telescopes.
Galileo:
Hmhm… Excuse me… Did I just hear something like Thirty Metre Telescope? Did someone actually say that?
Optics kid:
Yes sir, I did mention it. It's an upcoming mega science project of which our country, India is a part.
Galileo:
Oh I see! According to what I heard somewhere today, this “metre” is supposed to be a measure of length that was defined in late 18th century. Isn’t it?
Optics kid:
Yes sir, it is. In the era of yours, people used "inch" as a unit of length measurement. And people in the modern era use “metre”, where 1 metre almost equals to 40 inches.
Galileo:
I can't believe my ears. Do you really have that 1200 inches diameter lens? I mean, thirty metre diameter lens?
Optics kid:
Umm, no sir. Not exactly...
Galileo:
Then what's this thirty metre telescope you're talking about?
Optics kid:
Sir, if you please allow us, we would love to share the knowledge about telescopes and TMT with all our friends present here.
Galileo:
Definitely, I would love to know what you people have done in 410 years after my “perspicillum”.
Optics kid:
Thank you!
As we all are aware of the fact that light makes us see, let's start learning about some basics about it.
~~~~~
(Rectilinear propagation of light)
(The Optics kid will explain the rectilinear propagation of light using a LASER pointer.
Optics kid will then use dust/ talcum powder to show the straight path of light.
The explanation will include the daily life examples showing us this property of light those may include obtaining an image without using lenses or using a pinhole camera.)
~~~~~
Galileo:
Ohh, holy science! We knew this is how the light travels. And that's how we could work on the equipment helping us magnify farther objects.
Our ancestors between 10th and 12th century studied the properties of lens. Lens, word that is derived from Latin word 'lens', which means lentil.
But, there is something in this lens that makes light bend. I would like to see if you have some lens demonstrations too.
~~~~~
(Refraction)
(The Optics kid will show the properties of water as a lens.
Here, the explanation of refraction will come.
This will be followed by properties of different types of lenses - water tank and lenses demo.)
~~~~~
Galileo:
Oho, oho! That’s something good to see.
Almost a year prior to my "perspicillum", Hans Lippershey patented the equipment combining lenses to make farther objects look closer in 1608. When I came to know about it, the idea of looking at the heavenly bodies closely from the earth haunted me. And I pursued the idea to make similar optical equipment of my own. It was using a lens 2 inches wide to collect the light.
Aah! Those were the days, when it was a challenge to study the heavens. Aha, fun days were those!
~~~~~
Telescope kid:
Yes sir! We have heard and read about the stories of those challenging days. And in your honour (bows), the perspicillum of yours is now known as “Galilean Telescope”.
Galileo:
(Bows politely) I am grateful for the honour, my friend.
Telescope kid:
If you please allow, I would like to show its working to our friends present here.
~~~~~
(Galilean telescope)
Telescope kid:
This is a type of Galilean telescope we use. It is also called as refracting telescope or simply a refractor. It uses a combination of lenses. A convex lens to collect the light from the source, it is known as an objective. The other convex lens to magnify the image of the source obtained, known as an eyepiece. Galileo, however used a plano-convex lens as an objective and a concave lens as an eyepiece.
Galileo:
Yes, that was my perspicillum. I remember, I used to look at the moon and it could show me the wonderful features on the moon… the highlands, the craters. Marvelous!
It could show me how Venus has phases like our moon.
It could show me the satellite objects revolving around Jupiter.
Heavenly experience it was!
(Telescope kid will show an assembled Galilean telescope.
Disassembling the same while Galileo is telling a story of how he used it to discover many beautiful things about "heavens",
Telescope kid with the help will make a ray diagram (using transparent tube Galilean telescope, incense stick or talcum powder and two parallel laser beams).)
~~~~~
Galileo:
Oho, oho! Too good.
I am also loving that green light beam you're using.
The powder, to show the path of it, light scattering by dust particles! That's how the stars twinkle.
The point sources far far away in the heavens, bright and lit, twinkle as the light from them enters our atmosphere made of some gas mass.
Oho, oho!
I see how the stars twinkle as seen from the earth!
Optics kid:
You are absolutely right sir. Provided we have no atmosphere between us and stars, they would appear just bright point sources of light; and would not twinkle.
The green light, we are using is the LASER, one of the most revolutionary invention by humans. LASERs are highly monochromatic and coherent and thus are powerful, unlike the light we get from our sun or other natural sources which is incoherent and spread across number of wavelengths.
Galileo:
Oho!
Optics kid:
That is, Mr Galileo Galilei, Father of Modern Observational Astronomy (bows).
Following the "perspicillum" made by Mr Galileo Galilei, sir, different people across the world started working on it. This resulted in a next design by James Gregory, Gregorian telescope.
The term 'telescope' derived from Latin tele means far and scopium means to look at, was used for this magnifying equipment after many decades.
James Gregory used a combination of concave mirrors to collect the light from source.
~~~~~
*(Telescope kid will show the design of Gregorian Telescope.)
Telescope kid:
On exploring further, people understood the importance of making the telescopes larger in size.
Using lenses bigger in size would be inconvenient as lenses are heavy. Heavy mass would result into sagging, restricting the fine movements of the telescope.
Thus, Gregory used converging mirror to collect the light.
(Optics kid will now show and explain how mirrors work.
Demos on reflection - types of reflecting surfaces, types of mirrors)
~~~~~
Galileo:
Oho! Smart work I must say. Did they make bigger mirrors then?
That is interesting. I wonder how those designs work.
I am sure, my friend, you must be having those demonstrations in your bag too.
Telescope kid:
Yes sir. Let us show you how mirrors revolutionised the telescopes.
~~~~~
Telescope kid:
Sir Isaac Newton discovered that white light disperses when it passes through a prism. This means, the sunlight gets splitted into its constituent colours.
*(Dispersion of light through a prism)
~~~~~
(Optics kid will show demonstrations on colour theory,
Explaining how colours are fun - primary and secondary colours, coloured shadows)
~~~~~
Optics kid:
Learning about the dispersion of light helped Newton to make a new design of a telescope to give clearer and sharper images of celestial bodies.
Newton came to know why the images using lenses are having some colourful aura around them.
*(Chromatic aberration)
Optics kid:
Yes, it was the objective or lens used to collect the light acting as it is composed of number of tiny prisms, focusing different wavelengths at different points.
And so began the era of reflecting telescopes.
~~~~~
(Telescope kid will show an amateur reflecting telescope and explain in brief.
Telescope boy/girl (+1) will make a ray diagram (using transparent tube Newtonian telescope, incense stick or talcum powder and two parallel laser beams).)
~~~~~
Galileo:
(Clapping with happiness)
Holy! Holy!
I wish I could be here to get indulged with all this beauty of optics.
I wish, I could be sitting right in front of the eyepiece of that giant Thirty Metre Telescope.
I am happy to witness the evolution of my perspicillum in these four centuries.
Very happy, very very happy!
Cheers, To the era of reflecting telescopes and the new technologies!
~~~~~
(The End)
✍ by Sonal Thorve
Concepts covered
- Rectilinear propagation of Light
- Instruments / objects that produce light, may need fire
- Reflection & Refraction
- Galilean telescope
- Gregorian telescope
- Cons of Galilean telescope
- Dispersion
- Colour theory
- Newtonian telescope
- Modern telescopes
*Demonstrations are mentioned in brackets ().
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