6F40.10 - Distortion due to Atmospheric Scattering

Astronomy Picture of the Day February 23, 2010
Code Number:
Demo Title:
Distortion due to Atmospheric Scattering
Refraction in a Medium, Atmospheric Scattering
Area of Study:
Optics, Astronomy
Variac, Light bulb (100 watt), Box for Light bulb, Scattering Screens, Coffee Creamer, Beaker, Stirring Rod, Overhead Masking Plate, Pine-Sol.

See also 6F40.10 in Astronomy.

Place the masking plate on the overhead projector.  Place the beaker of water over the hole in the masking plate.  Start adding small amounts of coffee creamer and stirring.  As more coffee creamer is added the color projected from the overhead should go from white to orange to yellow and then eventually to extinction.  During this process, you may insert different color filters between the light source and the beaker and observe how far each color travels into the beaker before it is absorbed or scattered.   If you put a mask on the overhead projector that has a hole in it that is much smaller than the diameter of the beaker you will observe a beam of light up through the beaker.  You can then use a Polarizer from the side of the beaker to observe and then extinguish that beam.

Hook the light bulb to the Variac. Place the light bulb in the blacked box. Hold the screens in front of the light and observe that the screens with greater amounts of particles give the fuzziest image (Atmospheric Scattering).

A couple of drops of Pine-Sol can be used in place of the creamer.  This is a timed reaction so it will take up to one min. for the solution to turn cloudy.

For a "timed" sunset, you can use a mixture of sodium thiosulfate and hydrochloric or sulfuric acid.   Mix the thiosulfate with water until you have a saturated solution.  When ready to use, dilute this saturated solution with 10 parts water.  Make another solution with 2 ml of hydrochloric acid in 400 ml of water.  Pour 50 ml of this into the diluted thiosulfate solution and observe the precipitation rate (This should turn milky white within 30 seconds).  Dilute one or both of the solutions further until the desired reaction rate is obtained.

A simple alternative for this demo is to use a small Maglite with a clear hot melt glue stick.  You will observe the blue light scattering out the side and the red light exiting from the end of the glue stick.

This demonstration can also be used to help explain the zodiacal light which is Sunlight scattered by interplanetary dust. 

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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.