I have always enjoyed rainbows, and since I did some studying on them, I realized there are multiple applications.

First some history. In 1867 Rene Descartes decided to study the properties of rainbows. He did many tests.

He found, the lower the sun is to the horizon, the larger the arch of the rainbow… Right at sunset, we would see a full semicircle of the rainbow with the top of the arch 42° above the horizon. However, the higher the sun is in the sky, the smaller the arch of the rainbow.

An example of a higher arc with the sun low in the sky vs

a lower arc with the sun higher in the sky

We find that we are seeing only one color from each raindrop. In looking at a rainbow, we are seeing the refracted light contributed from many raindrops. The raindrops lower in the sky give us blue and green light; the drops higher in the sky contribute red and yellow light.
The normal rainbow we see, is produced by one internal reflection of sunlight rays.

When you see a rainbow, the sun is behind you, and the rain either is ahead of you, or right on you. Of course, it doesn’t have to be rain, it can be any source of water.

Here is a nice example of a rainbow from a waterfall. Where the water spray ends, so does the rainbow.

Let's look at the types of rainbows, and see what applications we can draw. I would say for a base rainbow; our application is the earliest one we find in the scripture:

Genesis 9:16-17

"When the bow is in the cloud, then I will look upon it, to remember the everlasting covenant between God and every living creature of all flesh that is on the earth.” And God said to Noah, “This is the sign of the covenant which I have established between Me and all flesh that is on the earth.”

God uses it as a reminder of his covenant with all living creatures not to flood the full earth again.

The Moonbow is when a rainbow is caused by the sun first reflecting off of the moon:

As you might guess, they can be hard to see, due to the much lower lighting conditions. If we look at Psalms 89:35b-37:

I will not lie to David.
“His descendants shall endure forever
And his throne as the sun before Me.
“It shall be established forever like the moon,
And the witness in the sky is faithful.” Selah.

So even the moon can bear witness of God’s covenants, just like the Rainbow. With the moonbow, it's bearing witness to two covenants, which is cool. A covenant with David and one to us for no more world wide floods.

The Fogbow is a rainbow caused by the water droplets in the fog:

Since the droplets of water in fog are extremely small, the only color that can be generated from the normal rainbow would be a very weak blue. This reminds us that we are like fog: James 4:13-15:

Come now, you who say, “Today or tomorrow we will go to such and such a city, and spend a year there and engage in business and make a profit.” Yet you do not know what your life will be like tomorrow. You are just a vapor that appears for a little while and then vanishes away. Instead, you ought to say, “If the Lord wills, we will live and also do this or that.”

We need to remember we never know what tomorrow will bring.

There are many proverbs that are related to rainbows, but they all seem connected to what is called the Red rainbow:

The red rainbow is formed at sunset and sunrise. The sun’s rays travel longer paths through the lower atmosphere where they are scattered by dust and air molecules. Short wavelength blues and greens are scattered more, leaving the remaining transmitted light more rich in reds and yellows. The end result, is red rainbows.

Back to the proverbs:

“Rainbow at night, shepherd’s delight; Rainbow in morning, shepherds take warning.”
Related to that one…. “Red sky at night, sailor's delight. Red sky in morning, sailor take warning”
“If there be a rainbow in the eve, It will rain and leave; But if there be a rainbow in the morrow, it will neither lend nor borrow”
“Rainbow to windward, foul fall the day; rainbow to leeward, damp runs away”

It's also Biblical, Jesus mentioned it in Matthew 16:1-4:

The Pharisees and Sadducees came up, and testing Jesus, they asked Him to show them a sign from heaven. But He replied to them, “When it is evening, you say, ‘It will be fair weather, for the sky is red.’ And in the morning, ‘There will be a storm today, for the sky is red and threatening.’ Do you know how to discern the appearance of the sky, but cannot discern the signs of the times? An evil and adulterous generation seeks after a sign; and a sign will not be given it, except the sign of Jonah.” And He left them and went away.

From this we learn, do not test God & Jesus and ask for signs.

Back to the proverbs, they are pretty logical when you remember that to see a rainbow, rain must be falling in part of the sky and the sun must be shining in the other part of the sky.

To see a rainbow or red sky, a person has to be facing the rain with the sun at your back.
When we see a rainbow at night we are facing east and towards the rain.
When we see a morning rainbow, we are facing west and towards the rain.
In this part of the world, the clouds and wind mostly travel west to east, so rain in the morning from the west would eventually reach us.

You might have heard of a double-rainbow:

Very pretty. Note that the second rainbow is more faint, and the colors are reversed. The secondary rainbow comes from two internal reflections with the rays exiting the drop at an angle of 50° rather than the 42° for the primary rainbow's color red. Blue light emerges at an even larger angle of 53° . This effect produces a secondary rainbow that has its colors reversed compared to the primary.

Since the secondary rainbow reflects in the raindrop twice, it is not as bright as the primary rainbow.

The colors being reversed tells us that sometimes God will need us to change direction, as found in Acts 8 (below is 8:25-27A, 29-32,36-39a):

So, when they had solemnly testified and spoken the word of the Lord, they started back to Jerusalem, and were preaching the gospel to many villages of the Samaritans.
But an angel of the Lord spoke to Philip saying, “Get up and go south to the road that descends from Jerusalem to Gaza.” (This is a desert road.) So he got up and went; and there was an Ethiopian eunuch ...Then the Spirit said to Philip, “Go up and join this chariot.” Philip ran up and heard him reading Isaiah the prophet, and said, “Do you understand what you are reading?”And he said, “Well, how could I, unless someone guides me?” And he invited Philip to come up and sit with him. ... As they went along the road they came to some water; and the eunuch said, “Look! Water! What prevents me from being baptized?” [And Philip said, “If you believe with all your heart, you may.” And he answered and said, “I believe that Jesus Christ is the Son of God.”] And he ordered the chariot to stop; and they both went down into the water, Philip as well as the eunuch, and he baptized him. When they came up out of the water, the Spirit of the Lord snatched Philip away;

Talk about a major change of direction that last time. But three times in this passage, not because of anything he did wrong, but because God needed him somewhere, we saw God change Philip’s direction. We need to be open to God changing our direction to fit his needs.

Next on our list, is the very rare twinned rainbow:

This appears as two rainbows of different arcs from the exact same base. Rene Descartes and most other scientists assumed that raindrops are spherical. While this can easily explain the rainbow and even the double rainbow, it cannot explain the twinned rainbow. Models in 2011, showed that actual raindrops flatten as they fall, due to air resistance. This flattening is more prominent in larger water drops. Such large drops end up resembling the shape of hamburgers, and are therefore called 'burgeroids.'"

The twinning effect occurs when two rain showers of different sized raindrops combine. Each set of raindrops produces slightly deformed rainbows, which give us the twinned form.

In the church, we all come from the same base, Ephesians 2:19-20:

So then you are no longer strangers and aliens, but you are fellow citizens with the saints, and are of God’s household, having been built on the foundation of the apostles and prophets, Christ Jesus Himself being the corner stone

So Jesus is our cornerstone, though our personal arc and journey may be different, perhaps due to our different jobs, Romans 12:6-8:

Since we have gifts that differ according to the grace given to us, each of us is to exercise them accordingly: if prophecy, according to the proportion of his faith; if service, in his serving; or he who teaches, in his teaching; or he who exhorts, in his exhortation; he who gives, with liberality; he who leads, with diligence; he who shows mercy, with cheerfulness.

Each having a different job to do, we all are moving in one purpose, Philippians 2:2B:

...being of the same mind, maintaining the same love, united in spirit, intent on one purpose.

But within that one purpose, we could still have different arcs on that one narrow path. Matthew 7:14:

For the gate is small and the way is narrow that leads to life, and there are few who find it.

Then we have the Sun smile.

Rainbows are rarely seen in the winter, since you need rain, and in winter, we have snow. However, if the temperature is just right you can get ice crystals, and these form the Sun smile, an upside-down rainbow.

If we check out Hebrew 11:1-2,6:

Now faith is the assurance of things hoped for, the conviction of things not seen. For by it the men of old gained approval. And without faith it is impossible to please Him, for he who comes to God must believe that He is and that He is a rewarder of those who seek Him.

We find out faith, is how we get approval from God, our smile…

In the Supernumerary or Stacker rainbow, notice the colors are separated:

This is caused by some rays of the sun canceling each other out through what is called destructive interference, causing that color to be erased in a narrow band.
Sometimes we have to make sure we don’t interfere with other Christians that are not part of our own Church, Luke 9:49-50:

John answered and said, “Master, we saw someone casting out demons in Your name; and we tried to prevent him because he does not follow along with us.” But Jesus said to him, “Do not hinder him; for he who is not against you is for you.”

All of the different varieties of rainbows are awe inspiring. But did you know, we can’t see the full rainbow? More on that in a future devotion.

Sources:

http://www.scienceagogo.com/news/20120708192551data_trunc_sys.shtml
http://mirznanii.com/info/rainbows-essay-research-paper-rainbowsa-rainbow-is
https://www.quora.com/Why-does-the-rainbow-have-only-7-colours
http://ucsdnews.ucsd.edu/pressrelease/computer_simulations_shed_light_on_the_physics_of_rainbows/