Equinox

(I can’t help hearing the title of the UK arts programme in my head when I see that word. It’s a great percussive word.) But I’m really here to talk about the solar event, not the TV programme. The September “Equinox” occurs today but it isn’t equal day and night! Bang goes another of my certainties!

On 22 September at 14:49 UTC, the sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from north to south. This is the definition of the Equinox, not – as its Latin name implies – that we have equal night.

The sun does this North-South crossing on 22, 23 or 24 September every year. On any other day of the year, the Earth’s axis tilts a little away from or towards the Sun. But on the two equinoxes, the Earth’s axis tilts neither away from nor towards the Sun, but is perpendicular.

So everywhere around the world, the equinox happens at one moment: 14:49 UTC. (UTC or Coordinated Universal Time is the basis for civil time in many places worldwide. Also known as Zulu Time, it is much the same as Greenwich Mean Time (GMT) although it is more precise.)

That is going to be nearly ten to one in the morning of 23 September in Sydney; 15:49 in London and 16:49 in Malaga.

Yet again I am confronted by the fact that something I thought was so obvious – that the Equinox was all about the same period of day and of night – is actually NOT TRUE. There’s probably a broader message there – about it’s always worth questioning and searching for answers.

In answer to the other question: the equal day-and-night days are different depending where you are. I was in Perth, Western Australia, on Wednesday 19 September and that was the closest to the 12 hours between sunrise at 6:10 and sunset at 18:11 (05:49 to 17:49 in Sydney).

In Europe you have 3 more days to wait. Your equal day-and-night day is Tuesday 25 September. In London sunrise is at 06:52 and sunset at 18:51; in Malaga it’s from 08:09 to 20:08

courtesy of http://www.timeanddate.com/worldclock/astronomy.html

Another thing that surprises me is that the times can be so different I guess, if you take them at non-daylight-saving-adjusted they are closer – London would be 05:52 to 17:51. I hadn’t really thought about Malaga being so late-shifted. I thought time differences took care of that but I guess Malaga is strictly speaking in a different timezone or something – national boundaries trumping natural ones.

So that is my astronomical learning from this Equinox. And I’m looking forward to the Southern hemisphere summer.

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