Sunlight and rain can cause a rainbow.
Liquid precipitation is measured with a rain gauge.
Sunlight and liquid precipitation can cause a rainbow.
What can cause a rainbow?

(1) photosyntehsis
(2) tornadoes
(3) sun and hot weather
(4) snowfall and fog
(5) chemical messengers
(6) sun and liquid precipitation
(7) algae and plants
(8) photosynthetic pigments?