How to explain Gravitational lens to a child

By Eden Orion posted 08-26-2022 12:08


A few days ago I was called to give a popular lecture on the new James Webb space telescope.

The audience was mainly children and their parents.

"No problem" I said to the guy who ordered the lecture... and started to prepare.

Then, when I saw the paragraph that describes the telescope in general - I was frightened:

“The James Webb Space Telescope is a space telescope designed for infrared light observations and is considered the scientific successor to the Hubble Space Telescope and the Spitzer Space Telescope. "

How will I explain to the children this paragraph and what is contained in it in forty minutes and they will understand a thing?

In fact, in such a lecture, beyond the explanation of the telescope itself, some concepts such as the speed of light, the light year, what a star is, what a galaxy is, what gravity is and how it affects light must be explained! Atmosphere and spectroscopy and all this in less than 45 minutes! And without math formulas.

Not so simple!

So I started to gather the questions for myself:

  • Why do you even need to put a telescope in space?
  • Why can you see farther in space?
  • What does it mean to observe things very far away (including the speed of light and concepts like a light year)
  • What the hell is "infrared light" and why should you adjust the telescope to view this light?
  • What is the difference in size between a planet and a star, and why can't we even with the most sophisticated telescope in the world see planets of other stars, and if we can't see them, how do we discover them?
  • And if we've already managed to discover planets for other stars, how do we know what materials are on them and maybe there's water there

As I started creating the answers to the questions, I saw that if they were arranged in the right order, they would help answer all the more complex questions as well.

So I started by explaining what the atmosphere is, what it is made of and why it is important for the existence of life on earth and on the other hand it also blocks/filters some of the light that reaches us and that perhaps due to this blocking it is worthwhile to put a telescope in space so that we can see all the light without some of it being filtered.

I continued to explain that light has speed! And that the light that reaches us from the moon takes a little more than a single second to reach us, and the light from the sun about 8 minutes, so that actually if we look at the sun (with adequate coverage of course) we see it as it looked about 8 minutes ago.

Then we turned our heads up and saw stars. I explained that most of these stars are suns just like our sun but because they are so far away we only see them as points of light. how far The light that comes out of them takes many years to reach us. And when we look at the stars, we actually see a live broadcast of history for many, many years.

On that occasion I also talked about the difference in size between the sun and the planet (hundreds of thousands of times) and therefore because the stars are so far away and therefore we see them as points of light, we will not be able to see their planets.

Then I explained that if such a planet orbiting its star happened to pass between the star and the telescope observing it, it would hide very very, very… little of its light. And if we can see and measure this very small decrease in the light intensity of the star that repeats itself, we can deduce from this the size of the planet and its distance from the star it orbits and also the length of its "year".

And when they discovered 1, 2, 3, - there are already several thousand stars that have such planets. And for this discovery they even won a Nobel Prize.

Then, I had to explain the infrared thing. Here I have already decided to explain what electromagnetic radiation is, not really the matter of an electric field and a magnetic field that change perpendicularly to each other, but that both the radio we hear in the car, and the light and color we see, and the x-rays that allow us to see where our arm or leg is broken and where and how to fix it, all of these are electromagnetic radiation or simply "radiation" and what differentiates the various radiations is the wavelength.

I explained that light can be seen in several forms and that one of the forms to see radiation is in the form of a wave. Here I already showed a picture of a wave and explained that the distance between two peaks of hills or valleys is called wavelength and that the difference between one radiation and another is its wavelength. I showed a picture of the electromagnetic spectrum and it was emphasized that the visible light field is a very narrow part of the entire spectrum, and that if our eyes were more sensitive we could also see light that is beyond the visible light field and new worlds would open up to our eyes.

In the same drawing I also emphasized that the field of infrared radiation is much wider than visible light. But the most convincing thing was to show them a photograph of the same celestial object, the Eagle Nebula, as photographed in visible light (by the Hubble Space Telescope) and in infrared light. The difference in the amount of details leaves no room for doubt!

Between one explanation and another, I also explained the structure of the telescope, how the light passes between the different mirrors, and what would such a telescope look like if instead of all the mirrors there was a long tube with a lens on one side and an eyepiece on the other side? What was the length of the telescope then? (130 meters).

Then came the first images we got from the space telescope.

When the children saw the first image that the telescope sent us, the one that resembles the "deep field" image of the Hubble Space Telescope, most of them immediately asked: "What are these circular "smearings" around the big light in the center.

So I told them about Einstein, who discovered all his great discoveries with the help of his mind, paper and pencil... And among his other discoveries he discovered that large bodies like our sun and of course also galaxies, - can bend light rays. Yes, it sounds imaginary, but quite a few experiments have already been done with the aim of measuring whether this happens - and yes! It happens! Einstein was right that a heavy body can bend light rays. Then I explained that if behind such a heavy body there are other bodies that emit light, that heavy body will bend their light rays so that they appear around it, and in fact these arcs are a distant galaxy that is behind the bright galaxy in the image that it is almost as if we can see what is behind a wall! From such magic!

All the previous explanations helped me clarify what you see in the other images obtained from the space telescope.

I gave this talk four times that evening. The kids were fascinated!

The parents approached me at the end of each lecture and said that they had never seen their children so engrossed in something other than their phone screen and thanked me very much for that.


1 comment



08-27-2022 11:25

Thanks for posting such a great member report. I learned quite a bit from it all and appreciate the information.