Ibn Al-‐Haytham the Man Who Discovered How We

IBN AL-HAYTHAM THE MAN WHO DISCOVERED HOW WE SEE

IBN AL-HAYTHAM EDUCATIONAL WORKSHOPS

Ibn al-Haytham was a pioneering scientific thinker who made important contributions to the understanding of vision, optics and light. His methodology of investigation, in particular using experiment to verify theory, shows certain similarities to what later became known as the modern scientific method.

Themes and Learning Objectives

The educational initiative "1001 Inventions and the World of Ibn Al-Haytham" celebrates the legacy of Ibn al-Haytham. The global initiative was launched by 1001 Inventions in partnership with UNESCO in 2015 in celebration of the United Nations International Year of Light. The initiative engaged audiences around the world with events at the UNESCO headquarters in Paris, United Nations in New York, the China Science Festival in Beijing, the Royal Society in London and in more than ten other cities around the world.

Inspired by Ibn al-Haytham, exhibits, hands-on workshops, science demonstrations, films and learning materials take children on a fascinating journey into the past, sparking their interest in science while promoting integration and intercultural appreciation.

This document includes a range of hands-on workshops and science demonstrations, with links to fantastic resources, for understanding the fundamental principles of light, optics and vision. The activities help engage young people to make, design and tinker while better understanding the significant contributions of Ibn al-Haytham to our understanding of both vision and light.

Learning Objectives

ü Inspire young people to study science, technology, engineering and maths (STEM) and pursue careers in science. ü Improve awareness of light, optics and vision through Ibn al-Haytham’s discoveries. ü Offer an exciting learning experience that helps celebrate diversity and promote intercultural appreciation, mutual understanding and respect.

ü Engage young people to to make, design and tinker.

ü Honour the shared creative, scientific and cultural achievements of pioneering men and women, of

different faiths and cultures, throughout ancient civilisations.

Educational Workshops and Demonstrations

Build Your Own Camera Obscura (ages 10 – 15)

Ibn al-Haytham is credited with explaining the nature of light and vision. He carried out experiments using a dark room he called “Al-Beit Al- Muzlim”, or “camera obscura”, the device that forms the basis of photography. His experiments inside a dark room explained that light travels in straight lines. When light rays reflect off an object, they pass through a small hole and create an upside-down image on a surface parallel to the hole.

Materials Required:

A wooden build-it-yourself flat-pack camera obscura kit.

Learning Objectives:

• Learn to build your own camera obscura • Test the theory that the smaller the hole, the clearer the picture

Links to Ibn al-Haytham’s discoveries:

• Ibn al-Haytham is credited with explaining the nature of light and vision, through using a dark room he called “Al-Beit Al-Muzlim”, or “camera obscura” in Latin; the device that forms the basis of photography. • Ibn al-Haytham proved experimentally that light travels in straight lines. • Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes.

Instructions:

1. Stick the plastic lens to the front plate using sticky tape. The front plate is the one with the smaller hole.

2. Assemble the outer box using sticky tape if needed to hold it together. Remember to slot the front plate in as you stick the outer box together.

3. Stick the screen to the viewing plate. The viewing plate has a large round hole in it.

4. Assemble the inner box using sticky tape to hold it together. Remember to slot the viewing plate in as you stick the inner plate together.

5. Carefully slot the inner box inside the outer box. Make sure the viewing screen is towards the front of the camera obscura.

What Happens? Now your camera obscura is made and ready to use. Point it towards a brightly lit area and look through the viewing screen from the back. Now carefully slide the inner box backwards and forwards to get a clearer focus of the image you are looking at.

Details and Further Information: Camera Obscura kit by 1001 Inventions: http://inv.ecgroup.net/c-9-all-products.aspx

Cow Eye Dissection Demonstration (ages 18+)

We see the world because light enters our eyes. Our eye uses that light to make an image of the world—just as a camera uses light to make a photograph. In this fascinating workshop we will dissect a cow’s eye to demonstrate how every layer of an eye works. A cow eye is very similar to a human eye and this demonstration offers a deep understanding about sight and how the eye works through this step-by-step dissection process.

Materials Required:

• Cow Eye • White Tunic • Scissors • Scalpel • Dissecting Tray • Rubber Gloves • Goggles • Cleaning Materials • Anti-bacterial Hand Wash

Learning Objectives:

• Understand the anatomy and physiology of the cow’s eye • Appreciate the functions of each layer and the structure of the cow’s eye • Observe the similarities and differences between a cow’s eye and a human eye • Understand how vision works

Links to Ibn al-Haytham’s discoveries:

• Ibn al-Haytham was the first to discover how we can see and prove that we see because the light reflects off objects and enters our eyes. • Ibn al-Haytham believed that our eyes are connected to the brain, which has a role in what we see. • Ibn al-Haytham laid out new ideas about light, colour and vision in his Book of Optics. Ibn al-Haytham’s writings influenced mathematician Kamal al-Din al-Farisi, who drew the structure of the human eye based on Ibn al-Haytham’s ideas.

Instructions:

1. The white part is the sclera, the outer covering of the eyeball. The blue is the cornea, which starts as a clear colour but becomes cloudy after death.

2. Cut away the fat and muscle. Without moving our heads, we can look up, look down and look all around. Six muscles attached to our eyeball move our eye so that we can look in different directions. But cows and sheep have only four muscles that control their eyes. They can look up, down, left, and right, but they can’t roll their eyes like we can.

3. Use a scalpel to make an incision in the cornea. Cut until the clear liquid under the cornea is released. That clear liquid is the aqueous humor. It’s made of mostly of water and keeps the shape of the cornea. There’s also fat surrounding our eyeballs to keep them from bumping up against the bone and getting bruised.

4. Use the scalpel to make an incision through the sclera in the middle of the eye.

5. Use your scissors to cut around the middle of the eye, cutting the eye in half. You’ll end up with two pieces. At the front will be the cornea. In this eye dissection, we cut away all the fat and muscle so that we can see the eyeball. A clear, tough surface called the cornea covers the front of our eye and protects it. If we make a cut in the cornea, a clear fluid oozes out. That’s the aqueous humour, which is made of protein and water. The aqueous humour helps give the eye its shape.

6. The next step is to pull out the iris, which is between the cornea and the lens. It may be stuck to the cornea or it may have stayed with the back of the eye. Find the iris and pull it out. It should come out in one piece. You can see that there’s a hole in the center of the iris. That’s the pupil, the hole that lets light into the eye. The iris contracts or expands to change the size of the pupil. In dim light, the pupil opens wide to let light in. In bright light, the pupil shrinks to block some of the light.

7. Now you want to remove the lens. It’s a clear lump about the size and shape of a squashed marble. If you look at your eye in a mirror, you will see a coloured circle with a black spot in the middle. The coloured circle is the iris. The black spot in the middle of the iris is the pupil, a hole through the iris that lets light into the eye. In dim light, the pupil opens wide, letting lots of light in.

8. Here is the back half of the eye. With the cornea and the iris out of the way, you can see the lens. It looks grey in this photo, but it’s really clear. The clear goo around the lens is the vitreous humour. The eyeball stays round because it’s filled with this thick, gooey substance.

9. Put the lens down on a newspaper and look through it at the words on the page. What do you see?

The words look larger as you see them through a magnifying glass. You can use the lens to make an image, a picture of the world. That’s what the lens does in your eye. It focuses a picture of the world on your retina.

10. Now take a look at the rest of the eye. If the vitreous humor is still in the eyeball, empty it out. On the inside of the back half of the eyeball, you can see some blood vessels that are part of a thin fleshy film. That film is the retina. The retina is made of cells that can detect light. The eye’s lens uses the light that comes into the eye to make an image, a picture made of light. That image lands on the retina. The cells of the retina react to the light that falls on them and send messages to the brain.

11. Use your finger to push the retina around. The retina is attached to the back of the eye at just one spot. That’s the place where nerves from all the cells in the retina come together. All these nerves go out of the back of the eye, forming the optic nerve, the bundle of nerves that carries messages from the eye to the brain. The brain uses information from the retina to make a mental picture of the world. The spot where the retina is attached to the back of the eye is called the blind spot. Because there are no light-sensitive cells at that spot, you can’t see anything that lands in that place on the retina.

12. Under the retina, the back of the eye is covered with shiny, blue-green stuff. This is the tapetum. It reflects light from the back of the eye. Have you ever seen a cat’s eyes shining in the headlights of a car? Cats, like cows, have a tapetum. A cat’s eye seems to glow because the cat’s tapetum is reflecting light. If you shine a light at a cow at night, the cow’s eyes will shine with a blue-green light because the light reflects from the tapetum.

12. Look at the other side of the back of the eye. Find the optic nerve to see the separate fibres that make up the optic nerve. Pinch the nerve with a pair of scissors or your fingers. If you squeeze the optic nerve, you may get some white goo. That is myelin, the fatty layer that surrounds each fibre of the nerve.

What Happens?

The cow eye is fully dissected and every layer and component has been identified and explained. You now understand how your eye makes an image of the world. Knowing a little bit about lenses also helps, as the clear glass (or plastic) in a magnifying glass is a lens, like the lens that’s inside your eye.

Details and Further Information: Exploratorium: https://www.exploratorium.edu/learning_studio/cow_eye/coweye.pdf Video with instructions: http://www.exploratorium.edu/learning_studio/cow_eye/step01.html

Eye Model Demonstration (ages 8 - 18)

We see the world because light enters our eyes. Our eye uses that light to make an image of the world —just as a camera uses light to make a photograph. This demonstration offers detailed informationabout sight and how the eye works.

Materials Required:

• Eye model

Learning Objectives:

• Understand the anatomy and physiology of the human eye. • Understand the functions of each structure of the eye. • Understand how vision works.

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes. • Ibn al-Haytham believed that the brain plays an important role in vision. • Ibn al-Haytham laid out new ideas about light, colour and vision in his Book of Optics which he completed in around 1027. It became very influential.

Instructions:

Explain the structure and function of each part of the eye using the model.

Sclera: the white part of the eye is the sclera, which is the outer covering of the eyeball.

Iris and pupil: if you look at your eye in a mirror, you will see a colored circle with a black spot in the middle. The colored circle is the iris. The black spot in the middle of the iris is the pupil, a hole through the iris that lets light into the eye. The iris contracts or expands to change the size of the pupil. In dim light, the pupil opens wide to let light in. In bright light, the pupil shrinks to block some of the light.

Eye lens: you can use the lens to make an image, a picture of the world. That’s what the lens does in your eye. It focuses a picture of the world on your retina.

The retina: it is made of cells that can detect light. The cells of the retina react to the light that falls on them, sending messages to the brain.

Optic nerve and blind spot: the retina is attached to the back of the eye at just one spot. That’s the place where nerves from all the cells in the retina come together. All these nerves go out of the back of the eye, forming the optic nerve, the bundle of nerves that carries messages from the eye to the brain. The brain uses information from the retina to make a mental picture of the world. The spot where the retina is attached to the back of the eye is called the blind spot. Because there are no light-sensitive cells at that spot, you can’t see anything that lands in that place on the retina.

Eye muscles: there are 6 muscles controlling the movement of the eye. Without moving our heads, we can look up, look down and look all around. Six muscles attached to our eyeball move our eye so that we can look in different directions.

3D Glasses Workshop (ages 7 – 12)

In order to see things in three dimensions, each eye must see a slightly different picture.

Since our eyes are about two inches apart, they see the same picture from slightly different angles. Our brain then correlates these two images in order to gauge distance. This is called binocular vision, and 3D systems mimic this process by presenting each eye with a slightly different image.

One familiar form of 3D vision technology is red-blue glasses.

On the screen, images are projected in red and blue at the same time, showing the same view from two angles. The glasses filter the colours so that each eye sees a slightly different image, which the brain recombines into a single 3D picture.

Materials Required:

• The 3D glasses templates below, printed out on thick card to the size required • 2 small sheets of cellophane, red and blue • Glue • Scissors • Clear sticky tape

Learning Objectives:

• To understand how we see in 3D. • To understand how coloured lenses create a 3D effect from a 2D picture. • Demonstrate the 3D components, Height Width and Depth

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes. • Ibn al-Haytham believed that the brain plays an important role in vision.

Instructions:

1. Print out and glue, or tape this template on to a heavier piece of card. Then cut out the three templates below. Remember to cut out the eye-holes.

2. Once you have the three pieces cut out, glue, or tape pieces of red and blue cellophane on to the inside of the glasses. Be careful not to get the glue on the viewing area of the cellophane.

3. Finally, glue on the side panels to complete your own cool 3-D glasses.

4. Fold the end panels to complete your glasses and try them out on.

What Happens?

Once your glasses are fully constructed, wear them and try them out. Visit any website that has red-blue 3D images online – try searching for ‘anaglyphic images’ - and view in awe the 3D pictures using your own home-made glasses. You can also purchase a range of magazines dedicated to this topic from any good newsagent.

Details and Further Information: Arizona State University: The Paper Project: http://paperproject.org/PDF_files/3dglasses.pdf

I-Scura Model Building Activity (ages 12 – 16)

Materials Required:

• White Plastic Flip-Top Waste Bin Lid • Black Plastic Waste Bin • White Shower Curtain • 3 Dioptre Lens • Gaffer Tape • Scissors

Learning Objectives:

• Learn to build your own I-Scura which is a giant version of a camera obscura • Test the theory that the smaller the hole, the clearer the picture • Understand how light rays travel in straight lines • Use light rays to create a photographic image

Links to Ibn Al-Haytham Discoveries:

• Ibn al-Haytham is credited with explaining the nature of light and vision. He carried out experiments using a dark room he called “Al-Beit Al-Muzlim”, or “camera obscura”, the device that forms the basis of photography • Ibn al-Haytham proved experimentally that light travels in straight lines. • Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes.

Instructions:

1. Black out the inside of a laundry basket and a flip top litterbin with gaffer tape

2. Find a lens that has a focal length of the height of the bin lid. One option is to use a lens from a 4+ dioptre pair of reading glasses

3. Buy a cheap, thin white dust sheet

4. Gaffer tape the whole lot together

5. Put on somebody's head

What Happens?

Your home-made I-scura is now ready to us. Place it on your head and create stunning inverted images inside the I-scura by looking at brightly lit places and objects indoors and outdoors.

Images and design courtesy of Justin Quinnell. Details and Further Information: http://www.pinholephotography.org/

Kaleidoscope Activity (ages 8 – 12)

The word kaleidoscope comes from Greek words meaning "beautiful form to see". At the most basic level, a kaleidoscope is made of two or more mirrors or reflective surfaces positioned at an angle to each other, usually forming a V-shape or a triangle. A tube or case, often looking like a spyglass, is the body surrounding the mirror assembly. A collection of objects is positioned at one end of the mirrors, and there's an eyehole at the other end.

What you see when you look through that eyehole will never be exactly the same twice! The pattern of objects is reflected in beautiful ways by the mirrors inside.

Materials Required:

• A cardboard kitchen roll tube • Mirror Board • Small colourful transparent objects (e.g. beads, sweet wrappers, etc.) • Three transparent plastic discs • Scissors • Glue stick and sticky tape

Learning Objectives:

• Understand the principles of light and how a kaleidoscope works • Learn how geometry, symmetry and angles combine to form beautiful patterns • Find out if adding more mirrors to a kaleidoscope increases the number of reflections you see • See how the kaleidoscope image changes when you change the number of coloured beads (or other objects)

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham carried out many experiments with different types of mirrors to study the reflection of light. • Ibn al-Haytham proved experimentally that light travels in straight lines.

Instructions:

1. Begin by cutting your mirror card into three strips. The strips need to be 4.3 cm wide and 21cm long. Once cut, sellotape the three sides together to form a triangular prism. Make sure the shiniest sides face inwards. Push into kitchen roll tube so that the prism is flush at one end.

2. Cut two discs of plastic with a diameter of 5.3 cm. One disc needs to be totally transparent whilst the other needs to be frosted. If you haven’t got frosted plastic to hand then simply glue a piece of greaseproof paper onto a transparent disc. Put the transparent disc inside the tube so that it rests at the end of the prism. Tape into place.

3. Pour your beads into the end of the tube. Don’t over fill as the beads need to be able to move around.

4. Place the frosted plastic disc onto the end and secure in place with tape.

5. Turn the kaleidoscope over. At this end you need to tape a disc of cardboard (5.3 cm diameter) with a peephole cut into the centre. Glue a disc of black paper to the cardboard disc just to make it look a bit smarter.

6. Decorate the outer tube in any way you fancy to personalise the design.

What happens?

Your home-made kaleidoscope is now ready to use. Look through it and you will see the sunlight bounces off the coloured beads and plastic and is reflected in the mirror boards to create beautiful patterns, which you can see when you look inside. Experiment further using more mirrors and different types of objects to create amazing patterns.

Details and Further Information: http://www.minieco.co.uk/kitchen-roll-kaleidoscope/

Periscope Workshop (ages: 8 – 18)

A periscope is an instrument used to see something that is above a high wall or around a corner and not in direct sight. A simple periscope consists of an outer case with mirrors at each end parallel to each other at a 45-degree angle. This simple form is used to view wildlife, or to look over a crowd of taller people at an event. More complex periscopes use prisms instead of mirrors to provide magnification and better images. Therefore, these types are often used on submarines.

Materials Required:

• Shoebox • Two Small Mirrors with safety edges (cosmetic mirrors are suitable) • Pencil • Scissors • Tape • PVA Glue

Learning Objectives:

• Understand how light rays travel in straight lines • Understand the concept of reflection of light • Learn how a periscope works

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham carried out many experiments with different types of mirrors to study the reflection of light. • Ibn al-Haytham proved experimentally that light travels in straight lines.

Instructions:

1. Remove the shoebox lid.

2. Place one mirror on the side and near the bottom of the shoebox and trace around it using the pencil.

3. Place the second mirror at the opposite end of the box and trace around it too.

4. Cut out the traced areas to make a door flap and slant them at 45 degree angles.

5. Tape the two mirrors onto the two door flaps.

6. Keep moving the mirrors to adjust them so that you can see out of the top hole when you look in through the bottom hole.

7. Seal the adjusted mirrors into place using the PVA glue.

8. Finally, glue the shoebox lid back on.

What Happens?

Light from the object that you are looking at travels to the top mirror. It bounces off (is reflected by) the top mirror and changes its direction so that it travels down the shoebox. Then the light bounces off (is reflected by) the bottom mirror and changes its direction again to travel towards your eyes.

Details and Further Information: James Dyson Foundation: http://www.jamesdysonfoundation.com/make-a-periscope/

Invisible Glass Demonstration (ages 5 – 18)

You can make glass objects disappear! Glass objects are visible because they reflect some of the light that shines on them and bend or refract the light that shines through them. If you eliminate reflection from and refraction by a glass object, you can make that object disappear.

Materials Required:

• A glass beaker • Vegetable oil (preferably sunflower oil) or Glycerin • A Pyrex beaker (smaller in size) • A Pyrex stirring rods or Pyrex test tubes (optional)

Learning Objectives:

• Understand visibility and invisibility of objects • Understand how light travels through different transparent materials • Understand the concept of refraction of light

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham observed that light refracts, or bends, when it moves through different materials. • Ibn al-Haytham carried out many experiments to study the reflection and refraction of light.

Instructions:

1. Pour some vegetable oil (or Glycerin) into the glass beaker.

2. Immerse the smaller Pyrex beaker in the beaker filled with the oil.

3. Notice that the Pyrex beaker becomes more difficult to see and disappears.

4. Experiment with a variety of glass objects made of Pyrex, such as stirring rods and test tubes.

What Happens? You see a glass object because it both reflects and refracts light. When light travelling through air encounters a glass surface at an angle, some of the light reflects. The rest of the light keeps going, but it bends or refracts as it moves from the air to the glass.

When light passes from air into glass, it slows down. It’s this change in speed that causes the light to reflect and refract as it moves from one clear material (air) to another (glass). Every material has an index of refraction that is linked to the speed of light in the material. The higher a material’s index of refraction, the slower light travels in that material.

The smaller the difference in speed between two clear materials, the less reflection will occur at the boundary and the less refraction will occur for the transmitted light. If a transparent object is surrounded by another material that has the same index of refraction, then the speed of light will not change as it enters the object. No reflection and no refraction will take place, and the object will effectively be invisible.

Vegetable oil or Glycerin has nearly the same index of refraction (n) as Pyrex glass (n = 1.474). Thus, in vegetable oil or Glycerin , Pyrex glass will disappear.

Details and Further Information: https://www.exploratorium.edu/snacks/disappearing-glass-rods http://www.arvindguptatoys.com/toys/Invisibleglass.html

Reversing Arrows Demonstration (ages 5 – 18)

Make an arrow on a paper changes its direction using a glass of water only!

Materials Required:

• Clear drinking glass • Water • Marker • Paper sheet

Learning Objectives:

• Understand how light travels through a lens • Understand how a convex lens works • Understand the concept of refraction of light

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham carried out many experiments with different types of lenses to study the refraction of light. • Ibn al-Haytham observed that light refracts, or bends, when it moves through different materials.

Instructions:

1. Draw two horizontal arrows on the paper sheet using the marker.

2. Put the empty glass in front of the paper.

3. Fill half of the glass with water and observe what happens to the arrow on the paper.

What happens? When the arrow is moved to a particular distance behind the glass, it appears to be reversed. When light passes from one material to another, it can bend or refract. In the experiment, light travels from the air, through the glass, through the water, through the back of the glass, and then back through the air, before hitting the arrow. Each time the light passes from one medium, or material, into another, it refracts.

Just because light bends when it travels through different materials, doesn't explain why the arrow reverses itself. To explain this, you must think about the glass of water as if it is a magnifying glass. When light goes through a magnifying glass the light bends toward the centre. Where the light all comes together is called the focal point, but beyond the focal point the image appears to reverse because the light rays that were bent pass each other and the light that was on the right side is now on the left and the left on the right, which makes the arrow appear to be reversed.

Details and Further Information: http://physicscentral.com/experiment/physicsathome/reversing-arrows.cfm https://www.childrensmuseum.org/blog/saturday-science-the-reversing-arrow

Disappearing Coin Demonstration (ages 5 – 18)

Make a coin disappears before your audience’s eyes. This is science not magic!

Materials Required:

• Clear drinking glass • Coin • Water

Learning Objectives:

• Understand how light travels through different transparent materials and media • Understand the concept of refraction of light

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham observed that light refracts, or bends, when it moves through different materials. • Ibn al-Haytham carried out many experiments to study the refraction of light.

Instructions:

1. Place the coin on a flat surface like a table.

2. Place the empty drinking glass over the coin.

3. Look through the side of the empty glass, you can see the coin.

4. Fill the glass with water.

5. Look through the side of the filled glass again, the coin disappears.

What Happens?

The science behind the Disappearing Coin is the refraction of light. When light rays travel through air, they experience little or no refraction. That's why you can still see the coin through the side of the empty glass. When you poured water into the glass, it was as though the coin had disappeared, but it was really just some bending light rays. After travelling through the water and the side of the glass, none of the rays were able to reach your eyes.

Refraction occurs because of the molecules in the substance that the light rays are passing through. Gas molecules are spread out. This is why little to no refraction occurs. However, when light rays pass through a substance such as water, the refraction is greater because the molecules are closer together. So when the light rays are traveling from the money through the water, they are refracted and cannot make it to your eyes.

Details and Further Information: Arvind Gupta: Toys from Trash: http://www.arvindguptatoys.com/toys/Disappearingcoin.html

Mystery Balloon Pop Demonstration (ages 5 – 10)

One balloon is blown up inside another, and you use a magnifying glass to focus light onto their surfaces. You expect the balloons to pop, but only the balloon on the inside bursts! The Mystery Balloon Pop is an experiment about the power of the Sun's rays and the absorption of light and heat.

Materials Required:

• Clear balloon • Black balloon • Magnifying glass • Sunlight

Learning Objectives: • Understand how a magnifying glass can focus light • Understand that black colour absorbs almost all light • Understand that the Sun’s rays carry light and heat

Links to Ibn Al-Haytham Discoveries: • Ibn al-Haytham carried out many experiments with different types of lenses to study the refraction of light. • Ibn al-Haytham observed that light refracts, or bends, when it moves through different materials. • Ibn al-Haytham proved experimentally that light travels in straight lines.

Instructions:

1. Blow up the clear balloon, but do not tie it off.

2. Insert the black balloon into the clear balloon partially, so that the opening of the black balloon is still accessible.

3. Blow up the black balloon until it is about half the size of the clear balloon.

4. Tie off the black balloon and push it into the clear balloon and tie off the clear balloon.

5. Focus sunlight on the black balloon inside using the magnifying glass. Only the black balloon pops!

What Happens?

When you use a magnifying glass to focus the Sun's rays, that spot, becomes incredibly hot. But why does only the black balloon burst?

Most of the light and its heat, pass right through the clear balloon's surface because it is nearly transparent. The black balloonabsorbs almost all of the light and heat – it barely reflects at all.

The heat absorbed by the black balloon from the focused sunlight quickly causes the balloon substance to weaken and burst.

Details and Further Information: Steve Spangler Science: https://www.stevespanglerscience.com/lab/experiments/mystery-balloon-pop/

Colour Mixer Activity (Ages 5 – 18)

Mix different colours of light and explore how colored light can be so cool!

Materials Required:

• Three torches of equal strength • Red, green and blue cellophane • Scissors • Three rubber bands • Cardboard cutouts of different shapes. • Different small objects (Pen, tennis ball, keys, etc..)

Learning Objectives:

• Understand that red, green and blue are the main shades of light. • Understand that mixing coloured lights results in specific colours, that are different to those made by mixing paints

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham observed the Sun, the moon and the stars. He wondered why the sky changes colours as the sun sets. He concluded that rays of sunlight refract, or bend, as they pass through the air around Earth. When light bends, it separates into different colours. • Ibn al-Haytham laid out new ideas about light, colour and vision in his Book of Optics. It was translated into Latin after Ibn al-Haytham died, and influenced many scientific thinkers that came after him.

Instructions:

1. Cover the three torches with pieces of red, green and blue cellophane and fix in place using rubber bands.

2. Shine the torches onto a white surface and move them to mix the shades in different combinations.

3. Put your hand in front of the three torches and see the colourful shadows.

4. Play with different objects and cardboard cutouts and observe their shadows.

What Happens?

Red, green and blue are the main shades of light. Each time you add one to another you get a new color. If you add all the three together, they will make white light. You can get any shade of light by mixing different strengths of red, green and blue light. Mixing red and green lights will give yellow, mixing red and blue lights will give magenta, and mixing green and blue lights will give cyan.

Images and instructions: Arvind Gupta: Toys from Trash: http://www.arvindguptatoys.com/toys/coolcolours.html

Colour wheel Activity (ages 8 – 18)

Mix different colours of light and explore how many new colours you can get.

Materials Required:

• Card sheets • Red, green, blue and yellow cellophane • Scissors • Glue • Press-stud • Two wooden sticks (tongue depressors) • Cardboard cutouts of different shapes.

Learning Objectives:

• Understand that red, green and blue are the main shades of light • Understand that mixing colored lights results in different colors of lights

Links to Ibn al-Haytham’s Discoveries:

Instructions:

1. Cut two 10-cm discs from the card sheets.

2. Cut five circular windows in each disc with a divider.

3. Stick different colors of cellophane on the circular windows using the glue.

4. Attach one wooden stick to each disk to act as a handle.

5. Assemble the two discs together by snapping the press-stud to the centres of the discs.

6. Rotate one disk while keeping the other stationary and see how mixing different colors can result in new colors.

What Happens?

Red, green and blue are the main shades of light. Each time you add one to another you get a new colour. If you add all the three together, they will make white light. You can get any shade of light by mixing different strengths of red, green and blue light. Mixing red and green lights will give yellow, mixing red and blue lights will give magenta, and mixing green and blue lights will give cyan.

Details and Further Information: Arvind Gupta: Toys from Trash: http://www.arvindguptatoys.com/toys/colourwheel.html

Bouncing Beam Demonstration (ages 8 – 18)

Materials Required:

• Square glass or clear plastic container • Water • Laser pointer • Dettol Liquid Soap

Learning Objectives:

• Understand the concept of reflection of light • Understand the concept of total internal reflection

Links to Ibn Al-Haytham Discoveries:

• Ibn al-Haytham carried out many experiments to study the reflection and refraction of light. • Ibn al-Haytham proved experimentally that light travels in straight lines. • Ibn al-Haytham observed that light refracts, or bends, when it moves through different materials.

Instructions: (this demonstration requires dark conditions)

1. Fill the square container with water.

2. Add few drops of Dettol liquid soap to the water.

3. Point the laser beam from the laser pointer directly at the container and notice how it bends (refracts) through the water.

4. Point the laser beam at an angle to the container. It does not come out of the water as it bounces (reflects) by the water surface.

What Happens?

When light hits an interface between two different media, it can behave in two different ways. Typically, the light partially refracts (bends) and partially reflects. There is a special phenomenon that occurs when light goes from a higher refractive index medium to a lower refractive index medium and above a certain incident angle, which called total internal reflection.

When light travels from a dense to a less dense medium, total internal reflection may occur if the light strikes the interface at a large enough angle. In this case, no light crosses the boundary into the second medium; it is all reflected.

We can take the interface between water and air as an example. Water has a higher refractive index than air. When light is propagating from water to air, for all angles less than a certain critical angle, the light gets transmitted through. But once the angle is larger than the critical angle; all of the light gets reflected.

Details and Further Information: Arvind Gupta: Toys from Trash: http://www.arvindguptatoys.com/toys/refraction.reflection.html

Bending Light Activity (ages 8 – 18)

As we all know, light travels in straight lines. However, in this activity we make it bend and travel through a curve!

Materials Required:

• Clear Plastic Bottle • Water • Bowl • Pointed Scissors • Torch

Learning Objectives:

• Understand the concept of total internal reflection • Understand how light can travel through fiber optics

Links to Ibn al-Haytham’s Discoveries:

Instructions: (this demonstration requires dark conditions)

1. Make a small hole in the plastic bottle near its bottom using the point of the scissors, carefully.

2. Hold your finger over the hole and fill the bottle with water.

3. Let the water pour out of the hole into a bowl.

4. Darken the room and shine the flashlight through the bottle and notice how light bends through the pouring water.

What Happens?

In our demonstration, light from the torch is bounced around inside the bending stream of water pouring out of the bottle through total internal reflection. This is why light travels so far through glass fiber optic communications cables carrying telephone calls, TV shows and Internet traffic.

Details and Further Information: Howtoons Instructables: http://www.instructables.com/id/Bending-Light/

Make a Rainbow Activity (ages 8 – 18)

Materials Required:

• Glass of water • Sheet of white paper • Sunlight streaming through a window

Learning Objectives:

• Understand that sunlight is composed of seven colors • Understand how rainbows can be formed

Links to Ibn al-Haytham’s Discoveries:

Instructions:

1. Move a table to a spot where the sun shines on it. (Do not look directly at the Sun)

2. Fill the glass to the top with water.

3. Carefully set the glass on the table so that it is half on the table and half hanging over the edge of the table.

4. Place the sheet of paper on the floor; adjust it and the glass of water until a rainbow forms on the paper.

What Happens?

Students will see that that sunlight is composed of a spectrum of colors: red, orange, yellow, green, blue, indigo, and violet. When the sunlight passes through the water, it is broken up into those colours.

Usually, the reason the light gets split up is because it is passing through a substance that bends the light. The different coloured wavelengths bend in different amounts. Red tends to bend the least, so it appears on the top of the rainbow, while violet bends the most and ends up on the bottom with all the other colours in between.

When we see a rainbow in the sky, it is usually when the Sun is behind us and it is shining through millions of tiny raindrops floating in the sky all of which are bending the light and projecting the rainbow.

Details and Further Information: Optical Illusion Blog: https://opticalillusion.wordpress.com/2008/07/21/how-to-make-a-rainbow-at- home/

Zoetrope Workshop (ages 8 – 18)

The zoetrope (pronounced ZOH-uh-trohp), invented in 1834 by William George Horner, was an early form of moving image device. It consisted of a drum containing a set of still images, which could be rotated in order to create the illusion of motion. Horner originally called it the Daedatelum, but Pierre Desvignes, a French inventor, renamed his version of it the zoetrope (from Greek word root zoo for animal life and trope for "things that turn.")

Materials Required:

• CD • Chapstick • Tape • Scissors • Template • Printer

Learning Objectives:

• Understand that animation is an illusion of motion from static pictures

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes. • Ibn al-Haytham believed that the brain plays an important role in vision. • Ibn al-Haytham observed the Sun, the Moon and the stars. He wondered why the Moon appears smaller when it’s high in the sky and larger when it’s low in the sky and determined that it was just an optical illusion.

Instructions:

1. Print the attached template and cut out along the dotted line using the scissors.

2. Fold the cut-out in half horizontally.

3. Cut out the viewing slots along the dotted lines.

4. Connect ends of the strip with tape and mount onto the CD with tape.

5. Use a Chapstick without the cap as an axle and spin the CD to the right. The images come to life as you view them through the viewing slots!

What Happens?

A zoetrope is a device that creates animation through the illusion of motion from static pictures. Like other motion simulation devices, the zoetrope depends on the fact that the human retina retains an image for about a tenth-of-a-second so that if a new image appears in that time, the sequence seems to be uninterrupted and continuous. You see that the images you place in the zoetrope are motionless, still images. However, when the zoetrope is spun, the images create an animation. Normally, images being spun in this fashion would simply blur together. However, because of the slits cut into the container, our eyes only observe brief instances of the images through the slits. As the instances fly by in rapid succession, our brains perceive the images as motion.

Details and Further Information: https://www.stevespanglerscience.com/lab/experiments/build-a-zoetrope/ http://www.instructables.com/id/Zoetrope/ http://whatis.techtarget.com/definition/zoetrope

Spinning Disc Illusion Workshop (ages 8 – 18)

Discover the secret behind making animations and cartoons and learn how our eyes and brain can be tricked into seeing static images in motion.

Materials Required:

• Card stock paper • Glue stick • Scissors • Hole punch • String • Templates • Printer

Learning Objectives:

• Understand that animation is an illusion of motion from static pictures

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes. • Ibn al-Haytham believed that the brain plays an important role in vision. • Ibn al-Haytham observed the Sun, the Moon and the stars. He wondered why the Moon appears smaller when it’s high in the sky and larger when it’s low in the sky and determined that it was just an optical illusion.

Instructions:

1. Print the attached templates on card stock or another type of thick paper. Cut the circular templates out using the scissors.

2. Paste the pictures back to back with one image upside down and the other right-side up using the glue and make sure that you align the images as perfectly as possible.

3. Punch holes in the far right and far left sides of the image. Tie a 30-cm length of string through one hole. Repeat with another 30-cm length of string in the other hole.

4. Wind up the strings by holding each string in one hand and twirling the disc.

5. Pull the strings tightly and the disc will start to spin rapidly. The two images blur into one combined image!

Templates:

What Happens?

The secret behind the Spinning Disc Illusion is the same that animators use to make cartoons. When images flash in rapid succession, like when you pull the strings taut, your brain cannot process them as individual images any longer. Instead, your brain takes the two images and combines them into one “hybrid” image. The brain can process up to 10 images per second as individual images. In reality, it is hundreds or even thousands of individual images being blurred into one moving image. The images are moving faster than the human eye!

Details and Further Information: https://www.stevespanglerscience.com/lab/experiments/spinning-disk-illusion-sick-science/

Spinning Light Disc Workshop (ages 5 – 10)

Ordinary light consists of the seven rainbow colours, red, orange, yellow, green, blue, indigo, violet. In this activity children learn that not only can white light be broken up into the rainbow colours, but also that the rainbow colours can be brought together to produce white light.

Materials Required:

• Thick White Card • Paint or Felt Pens– red, orange, yellow, green, blue, indigo and violet • Scissors • Pencil • Circular lid to draw around

Learning Objectives:

• Understand the principles of colour mixing and light • Investigate the splitting and mixing of light • Learn that not only can white light be broken up into the rainbow colours, but also that the rainbow colours can be brought together to produce white light • Learn about persistence of vision (i.e. that if things move fast enough the eye cannot distinguish between them and they merge)

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham laid out new ideas about light, colour and vision in his Book of Optics. It was translated into Latin after Ibn al-Haytham died, and influenced many scientific thinkers that came after him. • Ibn al-Haytham’s writings influenced mathematician Kamal al-Din al-Farisi, who investigated the colours of rainbows, using a glass sphere filled with water to show how the sunlight is bent twice by a water droplet. • Ibn al-Haytham believed that the brain plays an important role in vision. • Ibn al-Haytham observed the Sun, the Moon and the stars. He wondered why the Moon appears smaller when it’s high in the sky and larger when it’s low in the sky and determined that it was just an optical illusion.

Instructions:

1. Draw a circle using the lid onto the white card 2. Cut out the circle 3. Draw seven equal segments from the centre of the circle to the edge of the circle 4. Colour in each segment in each of the seven colours 5. Make two holes in the centre of the circle about 1cm apart 6. Use 1m long string and push it through the two holes and tie a knot 7. Put a finger through the end of each loop and flip the disc over the string several times until the string is well twisted 8. Pull your hands apart and let the string go slack, the disc should now spin

What Happens?

When the disc spins around at very high speed your eyes see the different shades but they get mixed up in your brain. So your brain sees a mixture of all seven colours, making white.

Details and Further Information: Discover Primary Science: http://www.primaryscience.ie/media/pdfs/col/rainbow_spinners_v2.pdf

Colour Contrast Illusion (ages 5 – 18)

Coloured objects may look different against different coloured backgrounds. In this demonstration, you will discover how colours seem to change when you place them against different-colored backgrounds.

Materials Required:

• Construction papers (yellow, purple, green, blue (two shades), and orange (two shades) in A4 size • Scissors • Glue

Learning Objectives:

• Understand the illusion of color contrast • Understand how eyes could see colours

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes. • Ibn al-Haytham believed that the brain plays an important role in vision. • Ibn al-Haytham observed the Sun, the Moon and the stars. He wondered why the Moon appears smaller when it’s high in the sky and larger when it’s low in the sky and determined that it was just an optical illusion.

Instructions:

1. Cut one sheet of orange paper in half lengthwise and glue it to cover up half of a blue sheet. This will give you a large sheet of paper that is half blue and half orange, which will be your background for other colors.

2. Cut two small squares from each of the colours, including squares of blue and orange of a different shades from that of the large sheets.

3. Make two matching, evenly spaced columns of coloured squares, one on the blue background and one on the orange background, and glue them.

4. From the same colours as the small squares, cut a strip of each colour wide enough that it can be placed over both columns at once for comparison.

5. Notice that two small squares of the same colour may appear to be different shades when mounted on different-coloured backgrounds. Place the comparison strip so that it touches both small squares of colour at the same time to verify that the squares are actually the same color.

What Happens?

Notice that two small squares of the same colour may appear to be different shades when mounted on different-coloured backgrounds. The back of your eye is lined with light-sensitive cells, including colour-sensitive cone cells. Your cones affect each other in complex ways. These connections give you good color vision, but they can also fool your eye. When cones in one part of your eye see blue light, they make nearby cones less sensitive to blue. Because of this, you see a coloured spot on a blue background as less blue than it really is. If you put a purple spot on a blue background, for instance, the spot looks a little less blue than it otherwise would. Similarly, a red spot on an orange background looks less orange than it otherwise would.

Details and Further Information: Exploratorium: Science Snacks: https://www.exploratorium.edu/snacks/color-contrast http://www.psy.ritsumei.ac.jp/~akitaoka/shikisai2005.html

Hole in Your Hand Illusion (ages 5 – 18)

You have two eyes, yet you see only one image of your environment. If your eyes receive conflicting information, what does your brain do?

Materials Required:

• Sheet of white paper (A4 size) • Transparent tape

Learning Objectives:

• Understanding the illusion of hole in your hand • Understand how brain combine images from both eyes

Links to Ibn al-Haytham’s discoveries:

• Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes. • Ibn al-Haytham believed that the brain plays an important role in vision. • Ibn al-Haytham observed the Sun, the Moon and the stars. He wondered why the Moon appears smaller when it’s high in the sky and larger when it’s low in the sky and determined that it was just an optical illusion.

Instructions:

1. Roll the sheet of paper lengthwise into a tube about 1.5 cm in diameter. Use tape to keep it from unrolling.

2. Take the tube in your right hand. Hold it up to your right eye and look through the tube, keeping both eyes open. You should be able to see the inside of the tube as well as what's around the tube.

3. Place your left hand, fingers pointing up and palm facing you, against the left side of the tube, about halfway down. Notice that your hand appears to have a hole in it.

4. Try switching your hands and your eyes. Hold the tube in your left hand, up to your left eye, and bring your right palm up against the tube, keeping both eyes open.

What happens?

You have two eyes, yet you see only one image of your environment. If your eyes receive conflicting information, one of your eyes sees a hole, the other sees a hand, your brain add the two images together, creating a hand with a hole in it! Some people find that this effect is stronger with one eye compared to the other. That's because one eye is likely dominant, which means your brain has a slight preference for visual information from that eye over the other. This is similar to being left- or right-handed, although your eye and hand preference don't necessarily match! Include image source.

Details and Further Information: Exploratorium: Science Snacks: https://www.exploratorium.edu/snacks/hole-in-your-hand

Optical Illusions Demonstration (ages 10 – 18)

For most optical illusions, it is the brain that is being tricked and not the eye. The eye only sees visual information, the brain interprets what this information is. For this demonstration you will need a laptop attached to a large monitor and a range of digital optical illusions similar to the ones shown below. There are many good sites available, for example http://www.michaelbach.de/ot/ Optical illusions give us an insight into how the brain processes visual information. There are many optical illusions that scientists still can’t explain. Nearly a thousand years ago, Ibn al-Haytham realised that our brains have to be involved in vision too. Now, we often say that 'seeing is believing'. But the optical illusions we have here will make you question your own senses.

Materials Required:

• Laptop • Monitor • A collection of digital optical illusion images (these can be sourced on many optical websites like - http://www.archimedes- lab.org/Gallery/new_optical_illusions.html and http://www.optics4kids.org/home/content/illusions/ )

Learning Objectives:

• Discovering more about optical perception, and about perception as a concept • Exploring the relationship between attention and perception • Understand the concept of visual deception due to the arrangement of images, effect of colours, impact of light source and other variable • Learn how the brain and the perceptual system function

Links to Ibn al-Haytham’s Discoveries:

• Ibn al-Haytham was the first to prove that we see because light reflects off objects and enters our eyes. • Ibn al-Haytham believed that the brain plays an important role in vision.

• Ibn al-Haytham observed the Sun, the Moon and the stars. He wondered why the Moon appears smaller when it’s high in the sky and larger when it’s low in the sky and determined that it was just an optical illusion.

Description of Illusions

Rotating Dots

• In this optical illusion, a series of dots rotate about a central ball. • Both sets of dots are rotating anti-clockwise. • Ask the visitors to focus their attention on one set of dots. • Now, ask them to now switch their attention to the other set of dots. • What direction does each set of dots rotate? • Focusing on one set of rotating dots will make the other set of dots appear to rotate in the opposite direction.

Breathing Square

• Watch the image on the screen, ask the visitors to describe what they see. • The blue object seems to expand and contract. • As more of the blue object is revealed, it becomes apparent that it is a rotating square. • The blue square will appear to expand and contract again as it is covered up.

Motion Silence

• Show the visitors that the dots on the screen are all changing colour.

• Now ask them to concentrate on the white dot in the middle of the screen. • What do they notice when the dots begin to move? • As the dots more, they seem to stop changing colour so rapidly. • If the visitors switch their focus from the white dot in the centre and follow the colour dots as they rotate, they will see that the dots are still changing colour as they move.

Stepping Feet

• In this illusion, visitors watch a blue and white square travel across a screen of black and white lines. • What do the visitors notice about the movement of these objects? • The blue and white squares appear to step one after the other. • When the lines are removed, it can be seen that both the white and blue squares are actually travelling together side by side. • When the lines are replaced, the stepping motion becomes apparent again.

Motion After Effect

• Ask the visitors to watch the spiral for a couple of minutes. • Get them to concentrate on the centre of the spiral without looking around. • Then instruct them to look away from the screen at any object. • The object they look at will appear to expand outwards for a few seconds. • Repeat the illusion, suggesting that they look at a friend’s face when they look away from the spiral. • The effect they are experiencing is called a motion after-effect.

Moving Circles

• Ask the visitors to slowly scan the image on the screen. • As they look around the screen, some of the circles will appear to rotate. • Reassure the visitors that there is no animation on this page, just a static image. • Ask the visitors to stare at the image in one place, the movement will stop.

Circle and Square

• Ask the visitors to tell you which circle is the largest. • Most will suggest that the circle in the square is the largest. • Both circles are actually the same size. • The circle in the square appears to be larger because we compare it to the size of the square it is in.

Ebbinghaus Illusion

• Ask the visitors to tell you which circle is the largest. • Most will suggest that the circle surrounded by smaller circles is the largest. • Both circles are actually the same size. • Regardless of relative size, if the surrounding circles are closer to the central circle, the central circle appears larger and if the surrounding circles are far away, the central circle appears smaller. • This illusion is similar to the Circle and Square Illusion. • The illusion was discovered by the German psychologist Hermann Ebbinghaus (1850–1909).

Kanizsa Triangle

• Ask the visitors to describe what they can see. • The central triangle (without border lines) appears to be brighter than the background. • However, both the background and triangle are the same colour and brightness. • In reality, the triangle doesn’t even exist, but our brain forms edges of the shape based on the cut-out circles and the bordered triangle. • Point out to the visitors that this triangle looks closer to the viewer than the other objects on the screen.

Jagged Edge

• Ask the visitors to watch the image on the screen. • What do they notice? • The rotating red image appears to jolt forwards and the stationary blue image appears to jolt backwards. • Only the rotating red image is moving.

Herman Grid

• Ask the visitors to look around the black and white grid. • What do they notice at the junction of the white lines? • They may see a small grey circle. • The grey circle is not there. • Ask them to stare at a particular junction of white lines.

• What happens to the grey image? It should fade away. • This illusion was published by Ludimar Hermann in 1870.

Penrose Triangle

• Ask visitors to study the image of the triangle. • Could this shape really exist? Why not? • This type of illusion is often referred to as an ‘impossible object’. • This illusion was popularised by mathematician Roger Penrose in the 1950s.

Impossible Cube

• Ask the visitors to study the image of the cube. • Could this shape really exist? Why not? • This type of illusion is often referred to as an ‘impossible object’.

Face and Vase

• Ask the visitors to describe what they see. • Can they see two faces looking at each other? Or, can they see a white vase shape?

Hidden Bird

• Ask the visitors to watch the bird as it flies over the image, can they see it? • When the bird stops, how easy it is to work out where it is? Are there any other birds on the screen? • It’s easy to see the camouflaged birds when they are moving, compared to when they are stationary. • Is it easier to find the birds when you repeat the experiment? Why is this?

Perceived Brightness

• Ask the visitors to study the image on the screen. • Which part of the image is the brightest? • The visitors will perceive that the centre looks brightest, but the level of illumination is the same across the whole screen. • Not only does our brain think the centre of the screen is the brightest, but our eyes also react to this perceived brightness also, with the iris become smaller to protect us from the “bright light”.

Contrasting Colours

• Watch the two sets of lines move from one side of the screen to the other. • Ask the visitors to describe their colour. • One set appears to be slightly orange, the other set slightly darker. • As the two sets of images pass each other, it will become obvious that both sets of lines are just red. • As the images move away from each other, they will return to their perceived colours.

Disappearing Spots

• Ask the visitors to look around the screen and describe what they can see. • Now get them to stare at the black dot in the middle. • What happens to the colours around the screen? • The colours should slowly fade away and disappear. • If the visitors blink or look away from the screen and back again, the colours will return.

Revolving Circles

• Ask the visitors to stare at the black dot in the centre of the screen. • Now get the visitors to move their heads backwards and forward (towards and away from the screen). • What happens to the two circles? • As you move your head towards the screen, the inner circle spins anticlockwise, the other circle spins clockwise. • The circles spin in the opposite direction as you move your head away from the screen.

Lilac Chaser

• Ask the visitors to watch the objects on the scree. What do they see? • Now get them to concentrate on the black dot in the centre of the screen. • With a steady gaze, they may see a blue/green dot rotating around the central black dot. • With a really steady gaze, the purple dots will disappear completely, leaving only the rotating blue/green dot. • However, there are only purple dots on the screen, the blue/green dot is not part of the animation, but is an after image.

What Happens? A presentation of optical illusions like these will work in any environment with audiences of all ages but should be viewed in full resolution and on a big screen to have the desired effect. Try out some of these illusions and many others with an audience to discover just how tricky it can be for your brain to accurately interpret the images from your eyes. Below are samples of amazing street art optical illusions, which take this concept of visual perception to the next level.

Details and Further Information: Michael Bach: Visual Phenomena and Optical Illusions: http://www.michaelbach.de/ot/

Useful Resources

1001 Inventions Resources:

• Ibn Al-Haytham Website: http://www.ibnalhaytham.com/

• Ibn Al-Haytham Educational Resources: http://www.ibnalhaytham.com/discover/education-resources/

• 1001 Inventions Website: http://1001inventions.com/

• 1001 Inventions Educational Materials: http://1001inventions.com/education

• 1001 Inventions Education Pack: http://www.1001inventions.com/files/1001iEducationPack.pdf

• 1001 Inventions Educational Books, Games and Products: http://inv.ecgroup.net/c-9-all-products.aspx

Other Resources:

• Exploratorium Science Snacks: https://www.exploratorium.edu/snacks/subject/light

• Arvind Gupta Toys from Trash: http://www.arvindguptatoys.com/fun-with-light.php

• Steve Spangler Sick Science: https://www.stevespanglerscience.com/lab/categories/experiments/light-and-sound/

• Howtoons Instructables: http://www.instructables.com/member/Howtoons/instructables/

About 1001 Inventions

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