With winter on its way out, many of us are looking forward to the onset of Spring, but what is the official starting date? Well this depends on whether you’re using the meteorological definition or the astronomical definition for determining your seasons.
Meteorological Spring
The meteorological spring is the most simple of the two answers because it merely splits the year into four equal seasons. Each of these contain three months using the conventional Gregorian calendar. This means that every year spring will begin on 1 March and will run through until the 1st of June when Summer officially takes over.
Astronomical Spring
The astronomical definition is a little less straight forward as it depends on the date of the spring equinox. This comes much later in the month, usually around the 20th and 21st. The spring equinox for us in the north, is the time that the sun is seen to cross over the equator and move into the northern hemisphere. On that day we are said to have an equal number of hours of both night and day which is where we get the Latin expression of Equinox. There are two of these Equinoxes each year, the autumn or vernal equinox being when the sun crosses back into the southern hemisphere in September.
For the In astronomer, the March equinox is very important as it is also the first point of Aries. This is the base point where all celestial activity tends to be measured from, which provides a recognised resource point for astrological and celestial observers. As such, the Astronomical Spring will run until the Summer solstice around June 21st. There is a further change around the 23rd September with Autumn and then winter then comes on or around the 21st of December.
The World is Skewed
We get our seasons simply because our world is on a tilt, spinning in an axis that is 23½ degrees off upright as it travels around the sun. For six months each of the year, either the northern or southern hemisphere is pointing slightly more towards the sun bringing the warmer temperatures of spring and summer. This means that on the astrological season’s calendar, at mid summers day or at the summer solstice, you would be 23½ degrees North of the Equator and the sun would be directly overhead. Similarly, on mid winter’s day or the winter solstice, the sun would be directly above 23½ degrees south of the equator. As a bit of trivia, these two extremes mark the outer edges of the area known as the Tropics.
Changing Times
This year we will change our clocks on Saturday 31st March, ‘springing’ them ahead in spring only to have them fall back again in ‘fall’. Whilst we refer to this as ‘British Summer Time’, elsewhere in the World it is referred to as Daylight Saving Time and it does exactly what it says in the description. It is to make better use of daylight by shifting one hour of work time from the morning to the evening. According to some sources, that simple time adjustment saves a considerable amount of energy for both business and private households alike.
