Sunsets in the LAB?

Fake Sunsets, they are a wonderful things, eh? There are lots of ways to show the Fizzix involved in the production of a sunset and why the sky is blue. These include:

Aquarium and Creamora : In a 5 or 10 gallon rectangular aquarium, sprinkle just a LITTLE bit of powdered coffee creamer and stir lightly. If you drop in too much creamer, this effect doesn't work at all, so be careful and try it out yourself first. Now, in a darkened room, shine a bright light source, I use a large Maglite Lantern, thru one side of the aquarium. What do the kids notice? When observed from the "front", the side where the light exits the aquarium, they notice a reddish/orangish hue. However, when observed off-axis, the side of the aquarium adjacent to the side the light is entering, perpendicularly to the path of the light beam, they will observe a blue-ish hue. Why? The suspension you have produced, creamer in water, acts light air and dirt and other molecules in the atmosphere. As light bangs into them, the litle guys, blue, are deflected or "scattered" around, just like little kids in a crowd of big kids. These you can see exiting the aquarium at the sides. Since the blue wavelengths are now scattered out, the remaining wavelengths, the "big" guys, make it all the way thru before they are affected by the little particles and you actually see what's left - reddish.

MagLite

Glue Stick Sunset; Same effect can be done using a basic hot glue gun stick. All you need is a typical translucent glue stick and a little MagLite-type flashlight. I found the thicker sticks give a better sideways blue hue. Shine the light thru the sorta translucent glue stick (obtainable at any hardware, hobby, or Sears store cheap) on axis - length-wise. You will observe the same effect as above. Looking INTO the long axis of the stick, you will see the reddish light still coming thru. However, looking at the stick from the side yields a blueins tinge. This is much better in a darkened room since it's on a small scale.

Chemical thing with Overhead Projector ; This one impresses the Administrator who observes you. Before the demo, prepare the following. (If you are like me - purely a Fizzix Guy - get a Chem Guy or Gal to help - I do...) Steps:

1.      Prepare a solution of hydrochloric acid (48 cc HCl / 52 cc water). About 20-30 total cc should be good per liter of water used. CAUTION : HCl CAN burn, be careful

2.      Obtain a LARGE beaker.

3.      Make a solution of about 90 g sodium thiosulfate (Na2S2O3) for every 100 cc of water in the large beaker.

4.      Cut a hole in an oak tag poster or other cardboard hunk so that you can cover the overhead projector EXCEPT where the beaker will sit. This eliminates any extraneous light waves interfering with this effect.

5.      Place the beaker of water and sodium solution on an overhead projector and turn light on. (Observe solution is clear and white light is seen exiting from every angle)

6.      Pour a small amount of the HCl solution into the beaker and let sit. If nothing is noticed after a minute or two, SLOWLY add more HCl. Let stand again. [Observe; As colloidal sulfur is released, the transmitted light on the screen turns from white to yellow-ish to orange-ish to red-ish. The solution, as the kids can see it off-axis, goes from clear to blue-ish.]

Why? Colloidal sulfur particles released in the solution thru a chemical reaction with the sodium solution scatter the short guys, blue, more than the big guys, red. Thus, lots of blue comes out the sides just like our sky! Meanwhile, the big guys, red, make it thru the solution and are transmitted up to the screen basically unhindered.

Summary Activity: Now, all these basically simulate the dust, dirt and other big particles in the atmosphere to cause all the colors we see. Follow this up with a couple weeks' observation activity where the kids actually have to observe the sunsets (AND sunrises if you want). They are to record specifically what colors they notice each day. You will need a coupla weeks of good weather for this. Extend the time if necessary. Collect the class' data and get the kids to make conclusions and follow up on it with a lesson about the pollutants in the atmosphere.
Observations are usually that the sunsets are "dimmer" on Mondays and "darker" or "richer" on Fridays. Why? The more pollutants, the more scattering. So there is less and less color left by the time the light gets to your eye. After a workweek of industrial and car pollution, the atmosphere contains much more than its share of crap. This causes great scattering for Friday. The atmosphere then has a chance to clean itself a little so the sunsets for Monday have less scattering and therefore aren't as spectacular. Cool, huh?

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