Every season begins twice: Here is why
Each season brings along its perks. While spring comes with its vernal showers and fresh blossoms, summer brings us the juicy mangoes and watermelons. Then there is monsoon, the favourite season of poets. Next comes autumn, or fall as the Americans call it, which brings us a variety of festivities. Finally, there’s winter when one can go on all kinds of adventures, with or without the snow in our country. That being said, when exactly does one season end and another begins? Is there a fixed timeline to it? Well, yes and no! In fact, as it turns out, seasons do not just begin once, but twice.
Seasons are defined in two different ways
Every year, one set of people welcome spring with the onset of March, while the other group says that it begins three weeks later, after the vernal equinox that falls on 20th or 21st March. Now, who do you think is right between these two groups? Well, both. Wondering how is that possible? Actually, seasons can be defined in two different ways, and both are equally right. So, one is astronomical season which depends on the Earth’s position as it rotates around the sun. Then there are meteorological seasons (the more common ones) which are simply based on annual temperature cycles. Interestingly, both of these divide the year into four seasons. The only difference is however when they start and end. Here’s what each of them means and what sets them apart.
Understanding astronomical seasons
As the name suggests, these kinds of seasons have got to do with astronomy. In fact, they are far older than meteorological seasons. After all, all ancient civilisations have looked up to the sky to determine the season. For instance, ancient Romans marked the dates of their seasons by either an equinox or a solstice. However, if you try and match them now, there will be discrepancies. Why? Because the calendars we use today isn’t the same as they used in those days.
Here’s how the method works. As we all know, equinoxes occur when the Earth’s day is split in nearly a half as the sun intersects the celestial equator. It happens every six months, once during spring (20th or 21st March) and once during autumn (22nd and 23rd September) when the Earth’s orbit and its axial tilt unite to bring the Sun directly above the equator, hence the name equinox. Now, astronomers usually prefer to start the spring and autumn on the days of equinoxes. As the seasons progress, the sun’s position too continues to alter, depending on the hemisphere one lives in, until the arrival of solstices.
Solstice, as we understand also happens twice every year and mark the brightest and darkest days of the year. This is when the Sun reaches its maximum or minimum declination and is thus marked by the longest and shortest days, 21st June and 22nd December respectively. Also driven by the Earth’s tilt, they mark the commencement of summer and winter.
While this method seems more or less simple, in reality it is quite complicated. It is because a year as we know in astronomical terms isn’t just 365 days, but a few hours, minutes and seconds more, which is why, leap year happens once every four year. As a result, astronomical seasons although start around the same time may have slightly different dates each year.
Understanding meteorological seasons
While astronomy continues to be an important field of study, humans realised long time back (in the 18th century) that it is hard to keep track of the celestial bodies such as the Earth and the Sun. Maybe that’s why they eventually turned to meteorological seasons, backed by climatologists and weather forecasters. In fact, these kind of seasons are more closely synced with annual temperatures and the calendar we follow in modern times. But the best part is of course, they are easier to understand. How? Well, meteorologists suggest that the year is divided into four seasons, with each of them lasting for three months, depending on the annual temperature cycle. Summer comes during the 3 hottest months, winter on the three coldest, while the spring and autumn come three months prior to them, respectively. So, this simply means, that in northern hemisphere, spring begins on 1st March, summer on 1st June, autumn on 1st September and winter on 1st December. Easy to remember, isn’t it? And in southern hemisphere, it is just the reverse.
Now, we know you think this isn’t always the case. Well, which is why, nowadays, both astronomical and meteorological seasons are looked upon. One is accurate, the other more consistent. This makes it easier to make all the forecasts as well. Okay, so the next time you are wondering when does spring begin, remember, it is both on 1st March and on the day of the vernal equinox!