Ira Sevaya, a natural phenomenon

by K.R. Abhayasingha

The Sri Pada season begins on the Unduvap Full Moon Poya day and the season ends on the Vesak Full Moon Poya day the following year. Accordingly, the next Sri Pada season will begin on the Unduvap Full Moon Day, December 16th this year and will end on the Vesak Full Moon Poya day, in May 2014.

Apart from the religious gains though worshipping the Buddha's foot mark, Sri Pada pilgrims get an opportunity to observe the environment and the sky without any obstacle specially during the night and early morning hours from a high altitude.

The most extraordinary sights are the colour changes of the eastern sky in the early morning and western sky in the late evening plus the shaking of the early sun in the eastern horizon which is termed as Ira Sevaya by Sri Lankans. This Ira Sevaya is the most expected sight from the Sri Pada.

With the scientific understanding of the nature, the man started to know the reality (or science) behind many of the natural events which had been explained based on concepts in old days. But as the scientific understanding had not gone to roots of all nations at the same speed for many reasons, the intellectuals still struggle to make the people aware of the reality behind many natural events because most of natural phenomena have been related to concealed forces, gods, ghosts and many extraordinary unseen powers or super natural powers.

Out of the many examples, rainbow, halo, colours of the sky, lightning, glistening spots of the atmosphere represent only a few. The natural event called Ira Sevaya also had been accepted by the majority of us as a superstitious event that is special only to Sri Pada (Samanola) mountain or Adam's peak. But this is a natural phenomenon which can be explained using the knowledge in Physics of light taught to school children in grades 12 and 13.

Observations

The Ira Sevaya, (fluctuation of sun's images a few minutes before sunrise) is one of the most beautiful and colourful visual observations one can see in the world if he observes the eastern sky in the early morning, a few minutes before the sunrise, from a high spot such as Adam's Peak. Mixed with all the effects of colouring, the shaking sun (really images of the sun) can be seen above the horizon. It is not a single image, but a multiple images. The images are seen in different locations before you see the actual sun above the horizon a little later and let us see how and why this happens.

As this... can be observed only in the morning just before sunrise, it should be a game played by rays of light. A light ray encounters a number of effects when it travels in a medium or passes a sharp edge, or travels through a common surface between two transparent media such as water and glass or air and glass or even between two air layers with different characteristics. Such phenomena are explained in Physics under the terminology of reflection, refraction, diffraction, scattering, diffusion and total internal reflection which differ in meaning from one another. A student of physics, who has studied these phenomena, can explain the science of the natural events such as rainbow, mirage, fluctuation of sun before the sun rise, eclipse, halo event and colourful patterns seen in the sky particularly in the north and south polar areas.

The apparent movement or shift of the sun a few minutes before the sunrise, when seen at the top of a hill, is caused both by Total Internal Reflection (TIR) and diffraction of the sun's light beams by the lower atmosphere very close to the earth surface at horizon.

Light rays undergo through Total Internal Reflection when they meet a common boundary between two media, one denser than the other (like glass and water, water and air or glass and air) provided that the incident rays travel through the dense medium before meeting the common boundary. When the incident angle exceeds a particular value (called critical angle), the rays are reflected towards the denser medium just like they get reflected by a plain mirror. In early hours of the day, the dawn, light rays from the un-risen sun are incident through the dense air which is at very low level, close to the earth surface, of the atmosphere towards rare (low dense) layers which are above surface layers and light rays get reflected towards the dense layer at boundaries separating dense/rare air layers.

Even though the actual position of the sun at this time is covered behind the horizon, by the solid earth, an observer/pilgrim at the top of a hill such as Sri Pada, can see the sun through the reflected light rays and he misunderstands that as the real sun while it is really an image of the sun. Those images of the sun are usually seen above the horizon.

Positions

As this so-called Ira Sevaya happens while the sun and the earth are moving, an observer sees a large number of images of the sun as the time passes. The observers may misunderstand the changing of positions of the sun's images as movements of the sun up and down in the eastern sky. Until the sun rises above the horizon, a person viewing the sky from a place at high altitude (Adam's peak or any mountain) can entertain this extraordinary event.

A few minutes later, the real sun rises above the horizon and as the total internal reflection does not occur now, one can see only one figure which is the real sun just at the horizon. This position of the real sun is usually below the positions of the images seen a little earlier by pilgrims. Ira Sevaya may also be partly a result of the diffraction of solar light beams at the tip of the earth in the early morning. A light ray finds the body of the earth as a tiny sharp edge and therefore it undergoes the phenomenon called diffraction at the earth surface and breaks the ray into a number of branches, which are transmitted in different directions. As in total internal reflection, a number of images are formed by diffraction too and an observer on a high location can see fluctuation of images of the sun before he sees the real sunrise.

The main phenomena Total Internal Reflection and diffraction cause the so-called Ira Sevaya a natural event occurring all over the world every day. The sun and earth are moving and rotating bodies.

The sun is the common energy source providing energy to the whole world from a distance of 150 million kilometres from us. It is not close to Adam's Peak. Before it rises over our horizon that can be seen from Sri Pada hill, the sun spends hours in the sky in other parts of the world.

The physics behind the event called Ira Sevaya is same for the whole world. Where-ever you are, you can observe this event provided that all necessary requirements are fulfilled. Some of the requirements are significantly high altitude of the observer, easily observable horizon, clear eastern sky, cloud and mist less environment.

The writer is a Former Director of Meteorology