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Congruent Angles and Angle Bisectors

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Starry Night

Credit: Ryan Wick
Source: http://www.flickr.com/photos/ryanwick/3461850112/
License: CC BY-NC 3.0

How do people make things that are far away seem closer? Telescopes, microscopes, and binoculars all use congruent angles to make objects appear larger and closer.

The Law of Reflection

When light bounces off a shiny surface, we call it reflection. Mirrors have a thin layer of shiny metal painted onto the glass. When you stand in front of a mirror, the light bounces off that layer and reflects itself back at you, allowing you to see yourself. 

Have you ever held a paper with writing on it up to a mirror? The writing appears backwards. This is because the light bounces off the mirror at an angle congruent to the angle it entered at—but in a different direction. The image you see in the mirror is actually the opposite of how other people see you.

Credit: Robert Lopez
Source: CK-12 Foundation
License: CC BY-NC 3.0

A reflecting telescope uses two different mirrors to focus and direct the light from distant objects. The first mirror is curved. When light reflects off it, it comes to a single point, called the focal point. The curved mirror makes the image stronger, clearer, and brighter. The second mirror is a flat mirror. It takes the image from the first mirror and redirects it so that it’s easier to see or record. The Hubble Space Telescope uses the law of reflection and congruent angles to take pictures of faraway stars and galaxies.

See for yourself: https://www.youtube.com/watch?v=--X9zfgZtS0

Explore More

Check out these links for more information on the law of reflection and reflecting telescopes.

http://www.physicsclassroom.com/Class/refln/u13l1c.cfm

https://pictures.royalsociety.org/image-rs-8462

http://science.howstuffworks.com/telescope3.htm

http://hubblesite.org/hubble_discoveries/hstexhibit/telescope/about.shtml

Image Attributions

  1. [1]^ Credit: Ryan Wick; Source: http://www.flickr.com/photos/ryanwick/3461850112/; License: CC BY-NC 3.0
  2. [2]^ Credit: Robert Lopez; Source: CK-12 Foundation; License: CC BY-NC 3.0

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