I took this photo of a rainbow in Sussex, southern England, late in the day, a little over a week ago.
Which way are we looking?
What’s the short-term weather forecast?
What sort of rain has created this rainbow, light or heavy?
What is the name of the dark area between the two rainbows?
Which colour sandwiches this dark area?
If we saw another sunset in half an hour…
a) Would it be bigger or smaller?
b) Would it be in the same place?
SPOILER ALERT ANSWERS BELOW!
We are looking close to EAST.
The rainbow is smaller than a semi-circle. (If it was a semi-circle the width would be twice the height of the rainbow, but it’s lower than that, see photo below). This tells us that the sun is low but still above the horizon. At this time of year that means the sun will be close to west (it sets north of west when we have passed the March equinox).
The centre of rainbows is opposite the sun, the sun is close to west, so… we are looking close to EAST.
The short-term forecast is for the rain to stop and the sun to come out. Most weather arrives from the west, so an afternoon rainbow usually means the rain is clearing to the east and there are clear skies to the west.
There are dark clouds and a strong red colour in the rainbow, a sign of large raindrops. It is a heavy rain shower.
The dark region between the bows is known as ‘Alexander’s Band’.
The colour red sandwiches the dark band. The primary, bright inner rainbow goes Red, Orange, Yellow, Green… towards its inner rings. Secondary rainbows have the same colours, going Red, Orange, Yellow, Green… but from the inside outwards. This leaves red on either side of the darkness. (The second rainbow is always much weaker because the sun’s light is reflected twice within each raindrop.)
A later rainbow would be bigger. The lower the sun, the bigger the rainbow.
The sun will move from left to right over the course of the day and so will any rainbows. A later rainbow would be a bigger version, to the right of this one. But each rainbow depends on the location of the sun, the rain AND the observer, so if you had moved at all during that time, the rainbow would do too. That’s why no two people ever see the same rainbow.
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