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Gallery 2

Corner Reflectors

Light reflected off adjacent mirrors creates reverse images and a retro-reflector effect.

How it works

Look into the mirrors and see yourself upside-down!

Things to try or ask around the exhibit

  • Look at your image from various vantage points and guess at which point you will be able to see yourself in each mirror.
  • Can you get away from your own reflection?
  • Gently clap your hands and listen to hear whether the sound will bounce back to you.
  • Stare directly into the 3-point corner of the corner mirror. The eye that appears to be closer to the corner is your dominant eye!

Background

If you can see a friend’s eyes in a mirror, they can see you!

Light bounces off a mirror’s reflective surface much like a ball bouncing off a hard surface. The angle at which it approaches is the angle at which it leaves.
To see yourself in a flat mirror, you need to stand directly in front of it. If you move to the side, light that bounces off you will hit the mirror at an angle and be reflected to someone who is standing at the other side of the mirror. So that person will see your reflection, while you see theirs!

The corner mirror in this exhibit is made of three mirrors that are all perpendicular to each other. Light first bounces off one mirror at the same angle at which it approached. It then hits a second mirror that is oriented at 90 degrees to the first mirror. This mirror serves to redirect the light back to its source along a path that is parallel to the original light beam. The net effect is that light is reflected off these mirrors and returned to its source. This type of mirror is also known as a retro-reflector.

Finding the science in your world

Bicycle reflectors are composed of many tiny corner reflectors that bounce the light from car headlights back into the driver’s eyes. A cyclist’s retro-reflector will beam light back at its source, but the cone of return is quite narrow. A driver sitting in a tall truck, bus or van will not see much of the reflected light, as they are seated too far above their headlights. This is why cyclists should use rear lights as well as rear reflectors.

NASA uses a retro-reflector on the moon to track its distance from Earth in the Lunar Laser Ranging Experiment. Scientists time how long a laser beam takes to travel to the moon and back and use this to calculate the moon’s distance (average is 384,467 km).

Radar reflectors are also mounted on sailing boats. These reflect radio signals from other boats, helping sailors detect each other when visibility is low.

Have you heard of the Venus Effect? The phrase comes from paintings of the goddess Venus who is looking into a mirror. People assume that Venus is admiring herself even though her face is pointed directly at the viewer of the painting, meaning that she is actually staring at the viewer instead!

This is often used in movies. The actor appears to be looking at themselves in the mirror, but if we can see the actor’s reflection, they can actually see the camera’s reflection instead!