No: The equinox did not occur in Kenya!

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

27 March 2016

This morning my ten-year-old daughter asked me: “How long does equinox last?”! Suddenly everyone knows about equinox, thanks to a meteorologist who appeared on national television and attributed the current unusually hot weather to this astronomicat phenomenon. She went on further (perhaps, farther) to explain that this is the time of year when the Sun comes closest to the Earth. She was dead wrong! Equinox has nothing to do with the distance between the Earth and the Sun.

To her credit, the meteorologist (I wasn’t able to catch her name) mentioned that this is a normal happenstance that occurs twice every year – in March and September – but the TV reporter made it sound as if this was a once in a lifetime event.

So, let’s put the record straight: equinox is that instantaneous moment that the sun comes directly above the Earth’s equator; or, astronomers would put it, when the Earth's equatorial plane passes through the centre of the Sun.

In primary school, we learn that the line joining North and South poles of the Earth is tilted at an angle of 23.5 degrees. Happily for teachers, nobody asks the all-important question: 23.5 degrees to what? I will leave you to wonder about that!

Because of this tilt, as the Earth goes round the sun, the position of the sun (viewed from here) appears to be oscillating between the two latitudes of 23.5 degrees North and South.

Starting at 23.5 degrees South in December, the sun crosses the equator in March and continues to reach 23.5degrees North in June. It then starts the return journey southward to cross the equator again in September and back to 23.5 degrees South in December the following year.

This movement has persisted over the last few millennia. Therefore, it is not right to attribute the unusual high temperatures observed in 2016 to the March equinox. Someone should have asked the meteorologist whether there was an equinox last year.

The first equinox this year occurred on at 7:30am on the 20th of March. Obviously, at 7:30 am, the sun was NOT overhead anywhere in Kenya. So, strictly speaking, the equinox did not happen in our country. At the exact moment that the centre of the sun crossed the equator, it was directly above a point in the Molucca Sea, 3.8km off the coast of Pulau Kajoa Island in the North Maluku Province of Indonesia.

What about the distance between the Earth and the Sun? This has no relationship to equinox. The path of the planet round the sun is NOT a circle; it is an ellipse. Therefore, the distance to the sun varies continuously. It closest to the sun in early January (2nd or 3rd) when it is about 147 million kilometres and gets to its farthest point in July (4th or 5th) when it is 152 million km.

Clearly, the atmosphere is a very complex system and it would be foolhardy to attribute changes in temperature to one or two effects.