Mirror Magic at AstroCamp

The heart of a reflector telescope is its mirror.  Kids are often taken aback when looking at land objects because they appear upside down.  Of course, celestial objects with the same telescope are upside down, too, but an astronomer cares less about an inverted image than, say, a birdwatcher does. That's why land-use scopes are usually refractors.

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A well known technique for projecting an image is to aim a mirror that is held inside a darkened room slightly off-center from a bright object outside the room.  A projected image shows up nicely on a white poster board in the darkened room, and that image will be upside down.  To bring the image into focus, you move the mirror closer to or further from the poster board.  

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To show AstroCampers some fun with mirrors, Astronomer-In-Residence Darren Drake sat inside with an 18-inch mirror aimed roughly toward kids who were outside in the sun.  Sure enough, the kids appear as a slightly muted upside down image.  

Then we switched from plain white poster board to a new poster board that still has clear plastic wrap around it.  The ensuing result is bizarre.  If you look over Darren's shoulder the muted image still appears, but within it there is a circular projection of the subject that appears extremely well defined and seemingly 3D!

Pictures don't do the effect justice, but it's enough to inspire silly-dancing and leaps of joy. mirror-jump.png 

In the image above, you can also see the faint reflection of Darren holding the circular mirror.  It is within that projected circular mirror that the mesmerizing effect is captured.

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