New Year is meaningless; Happy Perihelion day!

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

09 January 2022

Midnight is the beginning of a day; it is not the end of one. For this reason, we stayed up late on the evening of December 31st waiting for the New Year and, at the stroke of midnight (12:00am), we all shouted “Happy New Year!”. Unfortunately, New Year’s Day (January 1) has no physical significance; there is nothing special that happens in the natural world at the beginning of a year. It is just another random instant in the Earth’s journey around the sun!

Still, every year, something special occurs in the early days of January; the Earth reaches its nearest point to the Sun. Contrary to popular belief, the distance to the Sun is not constant. It varies from about 147 million kilometres (in January) to 152 million km (in July). That is a whole 5 million km of variation!

The reason for this is that the orbits of planets are NOT circular. They are ellipses – oval-ish in shape. Therefore, the distances from the sun are not a fixed amount throughout the year. This year, the Earth reached its closest distance at about 9:55 am on January 4. However, this point is not reached on the same day every year – it can vary by up to a few days. For example, last year, it occurred on January 2 at about 5pm.

Obviously, when the Earth is closer to the Sun, it receives more intense sunlight than when it is farther away. The difference in the two distances is about 3 percent. As a result, the sun’s intensity varies by about 6 per cent. (Nota bene: the 6 per cent is NOT arrived at by simply multiplying 3 per cent by two. It is a little more complicated than that and this case is just a coincidence).

Now, could this be the reason why January is so hot? Actually no. It turns out that, even though this month is very hot in Kenya, it is actually the coldest month on a global average, while July (our coldest month) is the hottest on a worldwide scale.

The reason for this apparent anomaly is that more than two-thirds of the earth’s land surface is in the northern hemisphere. Since the sun is in the North in July, it strikes more land than water. Even though its intensity is slightly lower, it is easier to heat up land that water; so, the average global temperature goes up.