Sunday 23rd at 1:54 UTC marks the point of equinox – that is when there is approximately equal day and equal night, making it the official start of Autumn.
As the Earth orbits the sun, in a slightly eccentric orbit and inclined at an angle of 23.5 degrees with respect to its orbital path, it will change its orientation with respect to the sun – that is half of the year the northern hemisphere will be pointing towards the sun and the other half the southern hemisphere will be pointing towards the Sun. Along this orbital path the Earth will also reach a point of equilibrium where neither hemisphere is pointing away or towards the Sun. This happens twice a year and is known as the equinox as the Sun shines directly on the Earths equator such that the length of day and night is approximately equal.
This year the Sun appears directly over the equator at 1:54 UTC on Sunday 23rd September, marking the official start of Autumn. As the Earth continues in its orbit the nights will get longer and the days will get shorter until the longest night on the winter solstice.
Coordinated Universal Time is the world time standard with the frame of reference being zero degrees longitude (e.g. London, United Kingdom) and with no adjustment for daylight savings.
Amira Val baker