The sun will rise overhead again

by K.R. Abhayasingha

The earth is a minute solid particle in the universe which spreads in space with dimensions of billions of billions of kilometres. In the primitive stages, 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 sense about what they observed, they developed many myths and concepts about the stars, the sun, moon and the planets.

Facts about the universe were not known to man even during the times of great philosophers and as a result, most of the concepts and beliefs about the universe have intruded into many religious teachings too.

But philosophers, and scientists, mathematicians especially those who lived after the 15th century changed the history of man, in understanding the reality of the universe through their excavations of the universe with the mind and with technology. The stories of what has been happening during the past 15 billion years and what is happening now in the universe are available now for reading in the computer.

As the 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 six months and it lies on different latitudes through the next six months in the other hemisphere. The location of the SSP changes from one hemisphere to the other 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 on March 20, 2016 on its northward movement and the SSP gradually moved northward and the sun rose overhead over Sri Lanka between April 4 (Southern tip) and April 14(Northern tip) this year. The Meteorological Department has computed the date and time of the sun being overhead in locations in our country.

As the SSP changes all the moments in the North-South direction over the globe, and its displacement in 24 hours is several kilometres, the sun never rises overhead at all the points and places on land.

The SSP changed gradually towards north and it was observed at a latitude of 23.5 north on June 22, 2016 after which it started moving southward. The latitude of the SSP is changing southward now and the sun will rise overhead of the equator again on September 22, 2016. During this fluctuation of the SSP, the sun rose overhead over areas near Point Pedro on August 28, 2016.

The SSP was over the Sri Lanka landmass southward during August 2016 and September 7 2016 and the sun will rise overhead over areas near Dewundara (Dondra) on September 7.

(The writer is a visiting lecturer, Post Graduate Institute of Science, University of Peradeniya and a retired director of Meteorology).