Under the Sun in April
Our earth is a minute solid particle in the universe which spreads in
space with dimensions of billions of billions of kilometers. In the
primitive stages, the man was unable to understand the reality of the
universe even though they used to observe the twinkling dots in the sky.
As they could not make any sense about what they observed, they
developed many myths and concepts about the stars, the Sun, moon and the
planets. They did not fail to name some powerful body or a character in
relation with many concepts.
about the universe were not known to man even in the periods of great
philosophers such as the Buddha and Jesus Christ and as a result, most
of the concepts and beliefs about the universe have intruded into many
religious teaching too.
But the great philosophers, and scientists, mathematicians,
especially those who lived after the 15th century, could change the
history of man in understanding the reality of the universe through
their excavations of universe with mind and technology. The stories of
what has been happening during the past 15 billion years and what is
happening now in the universe are available for reading through pressing
of the keyboard of a laptop.
As the whole world is aware now, our planet, the earth, makes one
vibration around its axis in 23 hours, 56 minutes and 4.1 seconds (not
in a 24 hour period as many people believe) while it moves along an
elliptical orbit around the Sun with least distance of 147 million of
kilometer and largest distance of 152 million of kilometers from the
pole of the ellipse where the Sun is located. The period of one journey
of the Earth around the Sun is 365.242 days (not in a 365-day period as
many people believe). Since the axis of the earth is inclined to the
normal direction of the plate of motion through an angle of 23.5
degrees, the point, or place, on the earth surface above which the sun
rises overhead is not fixed but is varying throughout the year. This
point is named 'Sub Solar Point' (SSP) in Astronomy and Meteorology. The
SSP lies on different latitudes in one hemisphere through a period of 6
months and it lies on different latitudes through next 6 months in the
other hemisphere. The location of the SSP changes from one hemisphere to
the other in every six months and it is the nature.
As it could be obtained either from Websites or from the
Meteorological institutes, the Sun rose overhead over the equator, the
line dividing the globe into two hemispheres, on 20th March 2016 at
10.00 hours Sri Lanka time on its northward movement and now the SSP is
gradually moving northward and the sun will rise overhead over Sri Lanka
landmass between 4th April (Southern tip) and 14th April (Northern tip)
Global astronomical institutes are responsible for preparation of the
tables with dates and times of solar overhead positions inter alia other
astronomical data. Once the computed data are available, it is the
responsibility of regional institutes to compute the dates/times of
positions of the Sun relevant to local positions. Sri Lanka
Meteorological Department has served the purpose and the Table 1 gives
the data for some locations in our country.
We have to understand some important facts in order to answer the
questions arising in our minds.As the SSP changes all the moments in
North-South direction over the globe, and its displacement in 24hour
time is several kilometers, Sun never rise overhead at all the points
and places on the land. Only the cities with Sun risen overhead in April
2016 are given in the table.
Also please do not feel embarrassing to query about the universal
behaviour. There are no special good or bad effectsby the Sun by rising
overhead to your village or area except for the uncomfortable feeling
due to direct solar radiation. This will cause increase of convection
leading to development of convective clouds which will produce
thunderstorms. Thunderstorms usually are accompanied by strong gusty
winds, lightning, tornado and water spouts.
With these solar equinoxes, the thunderstorms may be very intense
producing hazardous Tornado and also ice rain with minute ice particles.
The tornado or water spouts may result in rain with colourful water in
some areas, rain with small fish and frog in some areas.
You must not feel wonder to observe the above mentioned physical
events because these things are very common in April in every year.
Please do not regard them as unusual phenomena caused by any unseen
power. Let us understand the reality.
(The writer is a Visiting lecturer, Post Graduate
Institute of Science (PGIS), University of Peradeniya (Retired Director