At the moment, there seems to be much discrepancy online concerning when the first day of spring is. Many people posted "first day of spring" post's on social media yesterday which is greatly confusing, especially when google tells us it's the 20th March.
The Met Office explain this by telling us that while the 1st March is the first day of the meteorological spring, the 20th March is the first day of the astronomical spring.
Meteorological and astronomical seasons
As explained by the Met Office:
"Astronomical seasons refer to the position of Earth's orbit in relation to the sun taking into account equinoxes and solstices. Meteorological seasons are instead based on the annual temperature cycle and measure the meteorological state as well as coinciding with the calendar to determine a clear transition between the seasons."
"Since the seasons vary in length, the start date of a new season can fall on different days each year. This makes it difficult to compare seasons between different years and resulted in the introduction of the meteorological calendar. This splits the calendar into four seasons of approximately the same length. The astronomical seasons run approximately three weeks later than those of the meteorological calendar."
"The meteorological seasons consists of splitting the seasons into four periods made up of three months each. These seasons are split to coincide with our Gregorian calendar making it easier for meteorological observing and forecasting to compare seasonal and monthly statistics. By the meteorological calendar, spring starts on 1 March."
"The astronomical calendar determines the seasons due to the 23.5 degree tilt of the Earth's rotational axis in relation to its orbit around the sun. Both equinoxes and solstices are related to the Earth's orbit around the sun."