Rainbow Visibility

Just because there is rain and sunlight doesn't mean that a rainbow will be visible. When the sun is above 42 degrees the bow is below the horizon, so you won't see it unless you are in or above the falling drops. The same is true for the secondary bow where the sun needs to be below 51 degrees. In theory the secondary is visible for longer but in practice it is so faint that it is rarely noticed on its own.

The diagrams below were created using GraphDark, free software available on another part of this site., free software available on another part of this site. Time of day runs from bottom to top while days of the year run from left to right. The red areas are when the sun is below 42 degrees and orange when it is below 51 degrees. Click the summary images to get the full detail.

Rainbow visibility for London over much of the year. The light blue area in the centre is when the sun is too high for a natural rainbow. This situation lasts for several hours a day during the summer months. For more details on producing this diagram click here

The rapidly changing position of the moon produces a much more complicated pattern of visibility for moonbows. The sky also has to be dark enough of course, deep blue on the diagram. Generally the moon is only bright enough when nearly full, and showers often die out in the evening further reducing the chances of seeing a moonbow. For more details on producing this diagram click here