![]() The word “equinox” comes from Latin aequus, meaning “equal,” and nox, ”night.” On the equinox, day and night are roughly equal in length. This ends with the winter solstice, after which days start to grow longer once again. ![]() In the Southern Hemisphere, it’s the reverse.Īfter the autumnal equinox, days become shorter than nights as the Sun continues to rise later and nightfall arrives earlier. What Is an Equinox?ĭuring an equinox, the Sun crosses what we call the “celestial equator”-an imaginary extension of Earth’s equator line into space. The equinox occurs precisely when the Sun’s center passes through this line.įor those in the Northern Hemisphere, when the Sun crosses the equator going from north to south, this marks the autumnal equinox when it crosses from south to north, this marks the vernal equinox. In the Northern Hemisphere, the autumnal equinox occurs in September in the Southern Hemisphere, it occurs in March. The autumnal equinox is an astronomical event that marks the start of autumn (or “fall”). Due to time zones, the date of the equinox may differ by +/- one calendar day in your location. Finally, the word ‘equinox’ is descended from the Latin ‘equ’ meaning ‘equal’ and ‘nox’ meaning ‘night’ and is therefore very appropriate to describe the situation when the whole world has the same amount of daylight and night-time.Note: Dates listed above are based on Eastern Time ( UTC-5). The same is true for the southern hemisphere on the December solstice when the apparent southward shift stops. We say that the Sun reaches its northernmost limit on the solstice, even though of course it is not the Sun that is actually moving. It stops on the solstice day, before beginning to shift southwards again. However, as the June solstice is approached, the northward shift of the positions where the Sun is directly overhead at noon, slows down. Of course, the Sun never appears to stand completely still on any day of the year fortunately, Earth keeps turning. ![]() The word ‘solstice’ is descended from the Latin, ‘sol’ meaning ‘Sun’ and ‘sisto’ meaning ‘to stand still’. Another point to note is that those living on the Equator will always have equal night and day throughout the year.īut why are these astronomical events so named? On these dates, the noon Sun will appear directly overhead at the Equator and everywhere on Earth will experience 12 hours of daylight and 12 hours of night. These equinoxes happen on or around 21 March (the spring or vernal equinox) and 21 September ( the autumn equinox). In between the solstices are two positions in Earth’s orbit where neither north nor south poles are pointing towards the Sun. As a result, everyone in the southern hemisphere will experience their longest daylight hours this time. On or around 21 December, the south pole faces towards the Sun the north pole points away, and the noon position of the Sun is directly overhead on the latitude of 23.5⁰S (the Tropic of Capricorn). The opposite situation occurs at the December solstice (known as the winter solstice in the northern hemisphere and the summer solstice in the southern hemisphere). It also means that, on or around 21 June, the position of the Sun is directly overhead at local noon anywhere along the latitude of 23.5⁰N (the Tropic of Cancer) and everyone in the northern hemisphere will experience their longest daylight hours on that day. This means that, in the Arctic, the Sun shines for 24 hours a day, while in the Antarctic, it does not shine. The schematic below illustrates this situation.Īt the June solstice (known as the summer solstice in the northern hemisphere and the winter solstice in the southern hemisphere), the north pole points as far towards the direction of the Sun as possible, whilst the south pole points away. They occur because the Earth’s axis of spin lies at an angle (23.5 degrees) to the plane on which it orbits the Sun. The solstices and equinoxes are defined by Earth’s position in its orbit relative to the Sun. ![]()
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