Sun and Rain!
It is when there are two rainbows on a place rather than so above one rainbow is another therefore double rainbow
hot stars and interstellar gas, particularly hydrogen
Because light reflects off one rainbow onto the sky making a new rainbow.
Mari(Sea)-Sol(Sun)
There are conditions that permit viewing two rainbows at once. The primary rainbow is as one might expect, but a secondary rainbow is visible above the first one. There is a nice picture and a description posted at Wikipedia, and a link is included.
Plants and Animals!
Sfgjh and ghddh
the fog badge and the rainbow wing
Glucose and oxygen
Two eggs and Two Sperm.
The light bends and it is separated in the different colors of the rainbow.
They needed a keep because that was the strongest part of the castle and the portculis.
soil and sunlight
Heat and Alkenes
Land & Trade
Rainbow has two syllables.
Two