When we first start looking at telescopes for sale, in the back of our minds we are certainly thinking that we will spend most of our time examining the nighttime sky. And fact is, we probably will.
But that doesn’t mean that the daytime sky is devoid of interesting objects to examine.
One of the most beautiful daytime sights is the rainbow. It is somewhat of a rarity because in order to have a rainbow, we must have rain and sunlight at the same time.
What makes a rainbow? Where does it come from? Why does it form?
The easiest way for us to make a rainbow is to use a prism. We put a piece of glass in the sunlight and it separates the sunlight into bands of color. But why?
It is because the index of refraction of the glass is different from the index of refraction of air. Huh?… What the?…
I know – those are some pretty fancy words. (Physicists like to talk like that because they think it makes them sound cool.) What that really means is that light travels more slowly through glass than through the air. And when light travels from air to glass it bends or refracts. Why is that? Let’s take a ride down to the beach and find out why…
Well, here we are at the beach. We need something to do. I know – let’s drive our car into the ocean. Wait! Bad idea. Let’s use a rental car. Ya.
So let’s drive down the beach with the ocean on our left. At some point we turn to the left a few degrees and drive into the ocean. Because we’re entering the water at an angle, our left front tire hits the water first. This will cause drag on our left tire and the car will “pull” to the left. So driving from a surface that’s easy to drive on into one that offers some resistance causes our path to turn or “bend” (in this case, to the left).
That’s kind of what happens to our beam of light. It’s travelling along happily through “thin air” and WHOMP… it hits the glass at an angle and it bends.
Now, back to the beach. This time with two cars. We’ll use an old Model T with skinny tires and a modern formula 1 race car with ultra wide racing tires. We drive both into the water at the same angle. When the formula 1 car hits the surf, the broad tires offer a great resistance and the car pulls sharply to the left. It’s path bends a lot.
On the other hand, the Model T pulls only slightly. It’s thin tires slice through the water and offer less resistance.
So the formula 1 car’s path bends a lot more than the Model T. So both vehicles drive toward the water on parallel paths – but once they enter the water, they are at radically different angles. They have become separated from each other.
Sunlight is made up of many colors of light. Different colors have different refractive indices. What does that mean? It means that red light bends less than yellow light which bends less than blue light, etc. So just like the two cars became separated from each other when they smacked into the water, the paths of different colored light beams also become separated from each other when they smack into the prism.
So, why the rainbow? Are there prisms in the sky?
Yes there are – water droplets. Light travels more slowly through water than through air. So when light hits a raindrop, the different colors are bent at different angles and are separated from each other. The rainbow we see is cause by thousands of water droplets refracting light across the sky.
Want to get a good look at that rainbow next time
(or anything else in the daytime sky)?
How about a pair of binoculars from Nikon – a name renowned for quality optics…
CLICK ON THE GRAPHIC BELOW to get more info on
Nikon 7245 Action Ex Extreme 10 X 50 mm All Terrain Binoculars
Also great for looking at the moon at night…
Or…
Make Your Own Rainbow with this amazing device…
Kikkerland Solar-Powered Double Rainbow Maker
by Pasachoff and Filippenko. This fantastically illustrated book offers not only fundamental concepts, but also reveals exciting new developments in the field of astronomy.
