September Equinox will fall on September 23rd 2018 at 7:24 AM IST
Autumnal Equinox 2018 which marks the south ward motion of Sun will fall on September 23rd at 7:24 AM as per India time. At the mentioned time, the Sun will be directly above the equator and will start moving over the southern hemisphere bringing summer season in southern hemisphere and winters in the north. Also on this day, both the poles will receive sunlight. It is to be noted that Southern Hemisphere is celebrating spring equinox.
Due to the tilt of earth’s axis, which is 23.5 degree from the normal or perpendicular to the equator, there exist seasons on Earth. The tilt with revolution of earth causes seasons on earth and interestingly opposite seasons in Northern and Southern Hemisphere. We all have heard how Australia celebrates Christmas in summer is a representation of what how seasons vary things on planets. If the tilt of earth’s axis is towards Sun, the northern hemisphere will receive abundant light and will experience summer season whereas when the tilt is away from the Sun, the Southern Hemisphere will receive light in full and hence will experience summer.
When the tilt is neither towards the Sun now away, at that time, the equator is align in such a way that the Sun is shining directly above the equator marking its transition from north to south or south to north. Equinox is celebrated at that very time when the sun is exactly shining about the equator. This year it will be on September 23rd, 07:24 AM India time. This is called fall equinox or autumnal equinox in northern hemisphere whereas in the Southern Hemisphere it is called spring equinox .
On the equinox day, the day and night on earth are equal in length but this is only true for locations near equator. As you move northwards or southwards of the equator, the variation is significant. Another interesting feature to note here is that both the poles will receive sunlight although for a shorter duration after which the North Pole will be in the darkness until March 21st 2019, 03:24 am India time. Slowly the entire arctic circle will go into long durations of darkness before seeing the sun light after December 22, 03:57 am India time.