Astroblog: Unexpected Rainbows (Part 4)

Wednesday, April 29, 2009

Unexpected Rainbows (Part 4)

Rainbows are ephemeral, they can appear when we least expect then, then vanish away quickly. Rainbows are caused by refraction and reflection of light inside spherical rain drops (see here for a java applet showing how this works) or mist droplets , or prism like effects in glass doors and windows. To see rainbows, we need a fairly precise geometry between the sunlight and the refracting materials.

So we went to Victor Harbour on the weekend, during the biggest wet in South Australia for a long time. In a brief break between downpours, I went for a walk to Granite Island (penguin webcam here), as I walked across the causeway, a brief shower swept across and as it passed, this gorgeous rainbow appeared for a short time. This rainbow is somewhat unusual, as you can clearly see it in the foreground of the ocean. Often, if the rainbow reaches to the ground, it appears to merge into the ground (hence the "pot of gold" at the end of the rainbow legends). But it was very clear that the rainbow was floating in mid air, above the sea, and it shows in this image (click to embiggen). Shortly after, the rainbow faded away to nothing. However, I was surprised by more rainbows during that weekend.

Labels: miscelaneous, rainbows