Rainbows: Optical Wonders

RAINBOWS: OPTICAL WONDERS

The awe-inspiring sight of a rainbow has brought comfort and hope to people for thousands of years. Wordsworth wrote in an 1802 poem, “My heart leaps up when I behold a rainbow in the sky…” Though the rainbow can cause us to look up in wonder, it can be easily understood scientifically. 

The two basic ingredients of a rainbow are sunlight, particularly from a low angle, and water droplets. That is why rainbows appear after a rain shower. When the sun appears through the clouds, sunlight enters millions of water droplets bending at a slight angle because of the different densities of air and water (index of refraction), bounces off the back surfaces (reflection) of the droplets and then fans out into different colors in different directions upon exiting the droplets, deflected in the process (dispersion). This dispersion happens because each color has a different wavelength. White light is composed of a mixture of wavelengths each of which will refract at a different angle, thus creating the rainbow effect. 

The visible colors of the rainbow are always arrayed in the same order beginning from the outer bow: red, orange, yellow, green, blue, indigo and violet. Sometimes you can see a secondary rainbow, above the primary one. Its color order is reversed because the light within the droplet is refracted twice before it is dispersed. Rainbows can be circular. The ground cuts our rainbows in half, but if you view from above the ground, perhaps from a hot air balloon, you can see the full circular rainbow. 

After Newton explained the optical science of rainbows, the poet John Keats was dismayed. He wrote a poem in 1820 entitled Lamia, declaring that the scientific explanation had removed all the beauty and mystery from this wonder. 
“…Philosophy (science) will clip an Angel’s wings,
Conquer all mysteries by rule and line,
Empty the haunted air and the gnomed mine – 
Unweave the rainbow.”

Rather than removing the wonder, understanding the optics only adds to the awe of the rainbow. The rainbow is a sign of God’s love for the world (Genesis 9:12-16) and at the same time, demonstrates the amazing science of optics.

For more detailed analysis of the optics of rainbows, open this link in Wikipedia: Snell's Law of Refraction

Leaving in Glory

   

LEAVING IN GLORY

Here in the Rocky Mountains we are enjoying glorious fall colors as the aspen shimmer in the sunshine, flinging their golden leaves to the winds. These trees exhibit an explosion of color before the white curtain of winter snow descends. As I enjoy the artistry of this annual event, I ponder what I can learn from these beautiful trees about life and death?

The yellow color of the aspen leaf (carotenoid) has been present all through the summer, but remained hidden by the stronger green. Chlorophyll, the molecule that causes the green color, has been busy all summer photosynthesizing (putting together with light) sunlight and carbon dioxide, which produces glucose (sugars) and oxygen. This process is necessary for growth and life. But when the sun dips in the sky and the nights grow longer, the connection between the branch and the leaf is slowly cut off, corked up ‘so to speak’. As the amount of chlorophyll subsides, the yellow carotenoid becomes visible. When the sun shines through the golden aspen leaves on a clear day, the tree almost glows. It is beautiful.

Recently I attended a funeral for a friend, taken much too early by lung cancer. Although his life was shortened by cancer, he still touched many, from the homeless, to farmers, suburbanites, pastors, Bible teachers, and beyond. As his friends gathered to remember this dear Christian brother, a humble, gentle scholar, I was struck by the way he blessed us all, even in his death. I left the service feeling spiritually fed.

As the aspen tree begins to close down for the winter, preparing for the harsh days ahead, it does so with a glorious burst of color. I am reminded that soon my life will also end. My prayer is that, like the golden aspen leaf, as my life on earth grows weaker, the glory of Jesus Christ might grow stronger. John the Baptist said, “He must become greater, I must become less.” (John 3:30) In allowing Him to increase, His glory will become evident bringing joy and blessing to others.