I understand how rainbows are formed. Light reflecting on raindrops (that act like prisms). Shouldn’t that always happen if it rains?
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Not just any light but light coming from a specific direction. Diffuse light that went through the clouds won’t do anything. You need the sun to be behind you and the rain to be in front of you, so you only see a rainbow when you are between a patch of rain and a patch of clear sky with the sun.
If there’s sunshine on rainfall, then yes, rainbows will be visible somewhere, but only to people in the right position to see it i.e. close to the direct line between the sun and the rain.
Remember that rainbows are personal optical illusions, not physical things. They are only visible *to you* if *your eye* is in the right place at the right time. If you can see a rainbow, someone half a mile away likely can’t see one. No-one sees the exact same rainbow as anyone else.
In general it tends to be cloudy and overcast when it rains and you need direct sunlight to pass through the water to create a rainbow so rainbows happen consistenly at waterfalls, but not when it rains. https://youtu.be/usEcoMirsu8
Rainbows need lots of tiny water droplets suspended in the air.
That happens fairly often.
In addition to water in the air you also need the right geometry for the light.
The center of the rainbow is always directly on the opposite side of your head from the sun.
This means rainbows need the sun to be somewhat low near the horizon. That only happens at certain times of the day.
If the sun is too high up it won’t work.
Only when the sun is low can it shine from behind you to make a rainbow appear.
The sun rises in the east and sets in the west.
This limits when and where rainbows can appear.
No amount of water droplets in the air south of you will make a rainbow appear if the sun is southwest of you or directly above you.
Of course if you have a strong enough artificial light source you can make a rainbow appear anytime and anywhere here is enough water in the air.
for a rainbow to occur, the sun can be no higher than 40 degrees above the horizon, so that’s one condition that’s needed.
Rainbows are not actually all that rare, and it is possible to see a rainbow any time it is raining and the sun is shining at the same time. However, rainbows are often not very bright or distinct, and they may be hard to see if the sun is not at the right angle or if the rain is not heavy enough.
To see a rainbow, you need a combination of rain, sunlight, and the right viewing angle. When sunlight hits a raindrop, it is refracted (bent) as it passes through the raindrop and then reflected off the back of the raindrop. This causes the sunlight to be separated into its different colors, creating a spectrum of colors that appears as a rainbow.
To see the rainbow, you need to be standing in the right place, with the sun behind you and the rain in front of you. If the sun is too low in the sky, the rainbow will appear too close to the ground to be seen. If the rain is not heavy enough, the rainbow will not be very bright.
In addition, rainbows are often only visible for a short period of time, because the sun and the rain are constantly moving. This means that if you want to see a rainbow, you may need to be in the right place at the right time.
To see a rainbow, you need direct sunlight from behind you. Generally, you don’t see the sun when it’s raining.
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