The Vernal Equinox 2024 | In the Dark


Loughcrew (County Meath, Ireland), near Newgrange, an ancient burial site and  traditional place to observe the sunrise at the Equinox

Just a quick note to mention that the Vernal Equinox, or Spring Equinox, (in the Northern hemisphere) took place today, Wednesday 20th March 2024, at 3.06 UTC (which was 4.06am CET, where I am at, though I was sound asleep at the time). Many people in the Northern hemisphere regard the Vernal Equinox as the first day of spring; of course in the Southern hemisphere, this is the Autumnal Equinox.

The date of the Vernal Equinox is often given as 21st March, but in fact it has only been on 21st March twice this century so far (2003 and 2007); it was on 20th March in 2008, has been on 20th March every spring from then until now, and will be until 2044 (when it will be on March 19th). This year the equinox happened before dawn, so sunrise this morning could be taken to be the first sunrise of spring. It felt more like summer, sipping coffee on my terrace in Barcelona:

This reminds me of a strange conversation I had on a plane recently. I was chatting to the person sitting next to me, who happened to be British. When he asked what I did for a living, I replied that I was an astrophysicist. He then complained that he preferred the old days when the Spring Equinox was on March 21st, and that now that Britain was out of the European Union he hoped it would change back…

Anyway, people sometimes ask me how one can define the `equinox’ so precisely when surely it just refers to a day on which day and night are of equal length, implying that it’s a day not a specific time?

The answer is that the equinox is defined by a specific event, the event in question being when the plane defined by Earth’s equator passes through the centre of the Sun’s disk (or, if you prefer, when the centre of the Sun passes through the plane defined by Earth’s equator). Day and night are not necessarily exactly equal on the equinox, but they’re the closest they get. From now until the Autumnal Equinox, days in the Northern hemisphere will be longer than nights, and they’ll get longer until the Summer Solstice before beginning to shorten again.

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