From : Victoriafalls-guide.net

20 March 2012

Each full moon the Victoria Falls rainforest re-opens in the evening for special tours to witness the mystical magic of the lunar rainbow – spray and cloud permitting!

The Victoria Falls are one of the few places on earth where this natural phenomenon occurs regularly and where it can be witnessed with ease. And yet many people visit the Falls without knowing of this natural phenomenon but it is one of the most impressive sights of Victoria Falls.

Just like its day-time equivalent, the lunar rainbow or ‘moonbow’ is created as light is refracted by water particles in the air, ever-present from the spray of the Falls.

Lunar rainbows are much fainter than their day-time forms with which we are all so familiar. This is because of the lower amount of light reflected from the surface of the moon. Only when the moon is full and skies clear of cloud is enough light reflected to create a moonbow, which always occur in the sky opposite from the moon in relation to the observer.

The human eye finds it difficult to discern the colours in the moonbow because the light is usually too faint from the moon to excite the human eye cone colour receptors (this is true of all night-time vision). Hence, moonbows often appear to the human eye to be washed-out and white, without the concentrated colours of a day-time rainbow. However, the colours of a lunar rainbow do show in photographs with a long exposure.

The lunar rainbow is best seen at times of high water (April to July) when there is sufficient spray to create the moonbow effect. This spectacle is best witnessed in the early hours after moonrise, before the moon rises too high to create a moonbow that is visible to the ground-based observer.

The rainforest opens and operates tours the night before, night of and night after the Full Moon (see chart below for dates), when the moon is at its brightest and the chances of seeing a moonbow are greatest.

Take a good torch, the usual precautions against the spray, and arrange transport to and from the Falls – after dark the road between the Falls and town should not be walked as there are often elephant and buffalo in the area.

A moonbow tour can be arranged but is always difficult to confirm as it is dependant on the weather, if it becomes cloudy the tour will be cancelled.

If are are lucky enough to be travelling to Victoria Falls during a full moon we would highly recommend doing this tour.

The old debate as to which side of the Victoria Falls is best for viewing (we always say Zimbabwe, as you can walk along and view two-thirds of the Falls from this side!), is turned on its head for the lunar rainbow, which is generally accepted to be best viewed from the Eastern Cataract on the Zambian side, where the moon rises behind the observer, creating a lunar rainbow over the aptly named ‘Rainbow Falls’. The moonbow can also be viewed from the bridge.

The event of a regularly occurring natural moonbow is not unique to the Victoria Falls. Cumberland Falls (Kentucky, USA) is also famed for its moonbows. Moonbows used to occur at Niagara Falls, but do not occur any longer because of the surrounding light pollution – a warning to both Zambia and Zimbabwe to control the development of the area surrounding the Victoria Falls.

Moonbows were first know to be mentioned by Aristotle, in his Meteorology, circa 350 BC. People’s ability to see colour in a moonbow varies according to the quality of their night vision and the number and responsiveness of colour sensitive cones present in the retina of an individual’s eyes. Some people are able to see the subtle colours, and others only see faint shades of white.