No Two People Ever See the Same Rainbow
Seeing a rainbow has a lot in common with seeing in general. The experience is a subjective one, and has a lot to do with where your head us at, and how you look at things.
Rainbows fascinate just about everyone, young and old alike. In part, this is obviously due to their rarity, but I think it also stems from their ephemeral nature, appearing more as an apparition than an actual "thing." Are they there, or do they just appear to be? They move as you move, even as the landscape behind them stays behind. Walk closer to it and it refuses to stay where it was, refusing to allowing you to get any closer. They have no fixed distance from an observer, and seem to float in mid-air. They seem almost like an optical illusion, but they nonetheless do have a physical manifestation in some sense.
Rainbows are formed by an exact alignment of the sun in relation to your line of sight through atmospheric water droplets. Light from the sun (or some other point source) gets refracted though water droplets, and thus split into the various wavelengths of the visible spectrum. To create the appearance of a rainbow, the light source will always be behind you. The center of the arc of the rainbow will always appear directly in front of you, forming a line from the sun, through your head, to the center of the arc. The size of the rainbow's arc relates to how far from you the water droplets are that form it. If you were to draw a line from the position of your eyesight to the arc of the rainbow, this new line will always measure an angle of 42 degrees from the line through your head to the center of the rainbow. The particular angle comes from the optical physics that cause the phenomenon.
Rainbows usually have just a single arc that may or may not span from horizon to horizon. The colors of the rainbow will appear in concentric bands along this arc, with red on the outside limb of the phenomenon, and violet on the inner edge. A given ray of sunlight passing through a given water droplet reflects at varying angles off the curved surface that forms the back of the drop. Light from the outer band thus becomes "stretched" when compared to that coming from the inner band. This forms results in the range of wavelengths from red at approximately 750 nanometers to violet at around 400 nanometers. Given extremely fortuitous conditions, the light can get reflected a second time forming a second, dimmer rainbow arc outside the primary arc. Since this second band is a reflection of the first, the sequence of colors gets reversed, with red now on the inside and violet on the outer limb.
Perhaps the most fascinating thing about rainbows though is the subjective nature of their construction. A rainbow only exists due to the precise relationship of sun, water droplets and observer. Each water droplet contributes a specific part of the illusion based on the angle from it to your eye, and out to the center of the rainbow effect. And since no two things can occupy the same space at the same time, the rainbow you see will not be the same as what someone standing next to you will see. It may look quite similar, but it will be formed by a slightly different array of water droplets. The sun that forms my rainbow is the same sun as forms yours. It doesn't move. But to form a 42-degree angle arrayed out from my line of sight, different water droplets will be required when compared to those that contribute to the construction of the rainbow you see, standing only a few feet away. No two people ever see exactly the same rainbow. As one moves away from the ideal location, the brightness of a visible rainbow will begin to diminish, and at some point, the effect won't be visible at all. Seeing a rainbow is a very personal, subjective experience.
But is that really all that different from seeing anything?
I've long been interested in how different the resulting images taken by a group of photographers who visit a location together can be. Standing side by side, looking at the same subject matter, each will see it in their own way. But here, the difference in what each one sees doesn't come from a mere artifact of optical physics and refraction. Instead, the cause lies in the simple fact that each photographer is an individual, with his own background and perspective. Though they may be lined up in a row with their cameras and tripods, each photographer sees things in their own way.
Sometimes, I see photographers on such outings looking to the people standing next to them as if seeking for their guidance, perhaps feeling unsure of their own abilities and deferring to what they perceive to be the greater experience of their peers. But just as with seeing a rainbow, no one can see the world for you. Seeing anything is a very subjective experience.
If you want to find the best images you can, seek out your own subjective viewpoint. Don't just look to emulate others. Yes, it can be fun trying to figure out where Ansel Adams must have stood so you can copy those same incredible perspectives, but that can only take you so far. Imitation may be the most sincere form of flattery, but it's not the path to creative rewards.
At some point, you have to find your own incredible perspectives, your own subjective way of looking at things. In that lies your own personal path to the pot of gold at the end of the rainbow.