Science: How to Make Rainbow

How to make your own rainbow.

A common post-rainstorm natural phenomena, rainbows excite the imagination with visions of potted gold and leprechauns. While it is unlikely to find that proverbial pot of gold, making a rainbow, either one similar to natural rainbows, or one formed by an optical illusion, is an easy household activity.

Things You'll Need

• Glass method:
• Water Glass
• Flashlight
• Masking Tape
• Table
• Paper
• Scissors
• Or
• Mist Method:
• Hose with fine spray nozzle
• Bright sunny day
• CD method:
• CD
• Light Source
• Projection area (wall or ceiling will work)

Instructions

Glass Method

1. 

   Cover the front of the flashlight with masking tape.

   Cover the front of a flashlight with masking tape, leaving a straight slit an eighth of an inch wide.

2. 

   Fill a glass of water to a little below the rim.

   Fill a glass of water slightly below the brim to avoid spillage.

3. 

   Place the glass near edge of table.

   Place the filled glass at the very edge of a table or counter.

4. 

   Put a sheet of paper under the glass.

   Place a sheet of paper on the floor underneath the glass, approximately 30 degrees away from the edge of the table or counter (about half as far away from the edge of the counter as it is tall).

5. 

   Shine the flashlight through the glass.

   Shine the flashlight through the glass toward the sheet of paper. Play with the angle until a rainbow appears on the floor.

Mist Method

1. 

   Set the hose to fine spray mode.

   Hook up the hose and set nozzle to fine spray. If no nozzle is to be had, use thumb to create a fine mist.

2. 

   Spray the mist upward to see the rainbow.

   Spray the mist upwards. With your back to the sun, the rainbow should appear within the mist cloud.

3. 

   Keep trying until you see the rainbow.

   Play with the orientation of the nozzle and observe until a rainbow appears.

CD method

1. 

   Turn on the light.

   Turn on a light source.

2. 

   Hold the CD up to the light.

   Hold the CD, with the reflective side facing the light source.

3. 

   Play with the angle of the refraction until a rainbow appears on the wall or the ceiling.

Tips & Warnings

• Rainbows in nature form when sunlight is refracted through a water droplet, splitting white light into seven primary and secondary colors of the visible spectrum (as perceived by the human eye). The angle of refraction varies based upon the type of water you have (its ion and particulate content), and requires some fine tuning to local conditions. For the CD method, you can use multiple CDs to achieve overlapping rainbows, as well as projecting rainbows over different objects.

• Avoid looking directly at the sun when attempting the mist method. Remember, the rainbow will be forming as a function of water refracting (similar to reflecting off of a mirror) off of the individual droplets of water. Thus the rainbow will appear slightly opposite the direction from which the sun is shining.

References

• Rainbow mechanics: for an excellent description of why rainbows form