5 Optical phenomena you will probably never see.
The interaction between the atmosphere, particulates, light and water can create an array of amazing optical phenomena to feast our eyes on- some are more difficult to witness first hand than others. But, at least we have the facility of the internet to show everyone what they are missing, or provide an opportunity to the lucky few witnesses to gloat. Here are five of the rarest optical phenomena you are (un)likely to see, accompanied by a ‘what you need’ supplement to inform you when to have a camera ready and aimed in order to capture these awesome sights. May the odds be forever in your favour!
Number 5: The Fire Rainbow.
Technically, it is known as a circumhorizontal arc, but that’s not quite as much fun to say. This phenomenon is caused by clouds which contain water and ice droplets of nearly uniform size. These clouds diffract sun light which separates the light into different wavelengths, which we perceive as different colours. Although they look similar to rainbows in their colour arrangement; the mechanism by way the light is scattered to produce them is different. Rainbows are the result of refraction and reflection. When light is refracted, it is bent by passing through mediums of different densities, such as water. Reflected light bounces off a surface at an angle equal to the angle it hit the surface at. Diffraction, however, involves light waves being scattered into a pattern; creating what you see here.
-Cirrus clouds at least 20,000 feet in the air. -Optimum amount and distribution of ice crystals. -The sun angled so light hits the clouds at precisely 58 degrees.
The principles behind the formation of a Moonbow are quite the same as a rainbow; light is refracted as it passes through water droplets in the sky. These refractive properties of the droplets cause light to be split into a band of colours, more specifically the light spectrum. The only exception here is the light source is no longer the Sun, but the Moon (yes, it is technically still sunlight).
While most of us will have seen a rainbow at least once in our life time, a much fewer number will have had the pleasure to encounter the lunar equivalent. This is because, as the Moon is more variable than the sun, many conditions need to be just right.
- 1 full moon, and more particularly before and after the gibbous phase is favourable. -Plenty of moisture in the air. -The Moon to be no greater than 42 degrees above the horizon (otherwise no bow will form)
Number 3- Night Shining Clouds
These rare, mystifying clouds are formed under very restrictive conditions and are only seen in the summer, at latitudes north of 50 degrees. They originate in the layer called the mesosphere; making them the highest cloud formations in our atmosphere. While ordinary tropospheric clouds get their source of dust from things like desert storms, this is not a viable medium in the mesosphere where this dust simply cannot reach. Accordingly, it is speculated that these cloud formations utilise dust particles from outer space, making them extra awesome. Normally, they are far too faint to be seen, but they can be visible when illuminated by sunlight below the horizon.
-Latitude north of 50 degrees - Moisture -Space Dust
Number 2: The Green Flash:
The famed Green Flash is a meteorological phenomenon that occurs at sunset and sunrise. The green flash is viewable because refraction bends the light of the sun. The atmosphere acts as a weak prism, which separates light into various colours. When the sun's disk is fully visible above the horizon, the different colours of light rays overlap to an extent where each individual colour can be seen by the naked eye- for a fraction of a second!
-1 sun set (or rise) -A long, uninterrupted horizon. The ocean horizon works well. -A very clear day -The ability to not blink helps considerably.
First noted by scientist in 1989, sprites are bursts of electrical energy that form around 50 miles (80 kilometres) above the Earth. From what is known, sprites send pulses of electrical energy up toward the edge of space (the electrically charged layer known as the ionosphere) instead of down to Earth’s surface. It is speculated that ions and electrons floating about the atmosphere are heated by this field and glow red in response. Why are they so hard to see? Well, they last just a few milliseconds and since they are commonly associated with thunderstorms; clouds block the view from the ground. For this reason, many pictures of sprites have come from flights in orbit.
-1 thunderstorm -1 Space Station (optional)
All images courtesy of Wikimedia Commons
