Today is the Autumnal Equinox, which is when the sun passes directly over the earths’s equator, resulting in a day and night that are of the (almost) equal length of 12 hours each.
The equinox occurs because of the tilt of the Earth in relation to the sun – this is what creates the seasons.
The Earth’s tilt is 23.5 degrees relative to the plane of its orbit and although one revolution of the planet takes 24 hours – it differs depending on the time of year.
For the northern hemisphere, today marks the arrival of darker nights and colder weather. This pattern will continue until the winter solstice – the shortest day of the year. In 2018 this occurs on the 21st of December (it is the 22nd in 2019) which marks the change of pattern with the daylight hours slowly increasing for another 6 month cycle.
Of course, the reverse is also true in the Southern Hemisphere where today, the daylight hours continue to increase beyond the night-time hours and the spring season begins.
The word “equinox” is derived from Latin, meaning “equal night.” However, even if this is widely accepted, it isn’t entirely true. In reality, equinox events do not have exactly 12 hours of daylight.
There are two occasions each year when on the gregorian calendar an equinox occurs, the autumn (autumnal) equinox, which falls between the 20th – 24th of September and the spring (vernal) equinox, which occurs between the 19th-21st of March.
Many cultures and religions celebrate holidays and festivals around the equinox and Ireland hosts several ancient sites that align with the rising sun of the spring and autumn equinoxes. These include Carnbane West, Carnbane East and Patrickstown, Loughcrew which were all built some 5,000 years ago.