Colours of twilight

In the famous painting by noted artist Edvard Munch (1863 - 1921) called The Scream, the sky is filled with a scary red and a person is running away with great fear etched on his face. Face? No, it almost looked like a skull. This is considered to be one of the best paintings of the artist and has been appreciated by a great number of art critics.
Munch himself described this as a fearful experience as he looked up at the twilight colours at dusk on a particular evening and he “sensed” the scream of nature.
Not often do we see the twilight as a scary phenomenon. Instead it is seen as a phenomenon of nature that brings joy. Some art historians tried to dig out the past to understand the artist’s feelings of fear or if there was really something scary in the sky.

Twilight colours linked to volcano
And, they found an answer indeed. The twilight colours were indeed ghastly around 1884. The reason was the eruption of the famous Krakatua volcano which erupted in 1883 devastating the island and killing almost 10,000 people.

The tons and tons of dust pumped into the atmosphere create such wonderful after-effects. Thus one can have green sunset and sunrise too. Or maybe the blue moons in the literal sense. (Otherwise a blue moon is referred to as the second full moon in the same calendar month).

The quest for understanding the phenomenon started long ago. It started with the discussion on the colour of the moon during the total lunar eclipse which is light brown or orange.

Kepler rightly identified the source as the atmosphere of the earth which selectively bends the red colour of sunlight on to the moon by a process which today we understand as scattering. In the next few centuries many observers tried to quantify the colour of the moon during the eclipse; they meticulously noted down the colour at every lunar eclipse. Quite interestingly on some occasions the moon disappeared completely, no trace of orange or brown but just a dark circle.

It was in the late nineteenth century that scientists started putting things together; that eclipses were dark; twilights were colourful; that the sunset and rise were green or grey; and most importantly all these happened simultaneously. The data included descriptions in the Letters to the Editor columns in newspapers like The Gentlemen’s magazine. Another interesting compilation by Simmons showed that all these phenomenon were preceded by a volcanic explosion in some part of the globe or the other. The letters also helped in tracing the appearance of the events in different parts of the globe; the duration it took to migrate from the source (the region of the volcano) helped in mapping the wind pattern in the upper atmosphere and hence the discovery of trade winds.

Study of atmospheric dynamics
In the early part of the twentieth century, scientists were effectively using the volcano eruptions to study the dynamics of the atmosphere. The wind velocity and the amount of dust pumped up also could be estimated.

A research paper in 2004 has systematically put down all the data together from 1665. A clear indication of the disturbed transparency of the atmosphere following every volcano eruption is evident.

One of the interesting results in a paper from the scientists of Physical Research Laboratory, Ahmedabad, in Nature in 1983, was obtained by monitoring the twilight durations systematically from Ahmedabad. The erupting volcano was El Chichon in Mexico.

More recently, people have dug out traces of sulphur concealed in the ices of Antarctica as evidences of intense volcanic activity in the recent past. This in turn can be related to the warming sessions or cooling sessions in the history of earth.Thus the volcano is the key to understanding the dynamics of the earth’s interior as well as the atmosphere, although it appears to be disturbing the climate and accused for the airfreight chaos.