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Happy Spring Equilux

Today, Friday 18 March 2011,  it is the Spring Equilux throughout the UK (and possibly elsewhere too*) meaning that there are almost exactly 12 hours between sunrise and sunset.



This date differs from the Spring, or Vernal, Equinox (2321 GMT on Sunday 20 March 2011) for a variety of reasons, which I explain in a previous post but here is a list of sunrise / sunset times for a variety of towns and cities throughout the UK:

Town / City Sunrise Sunset
Aberdeen 0617 1817
Glasgow 0626 1826
Belfast 0632 1833
Newcastle 0615 1815
Manchester 0617 1818
Birmingham 0616 1817
Cardiff 0621 1822
London 0609 1809

As you can see the time between sunrise and sunset is not exactly 12 hours everywhere but this is the day of the year when that is closest to being true everywhere*. Yesterday the sun rose a couple of minutes later and set a couple of minutes earlier, and tomorrow the sun will rise a couple of minutes earlier and set a couple of minutes later, as the days lengthen.

Also, the reason that sunrise and sunset does not occur at the same time everywhere* is due mainly to the longitude of the town, the further east a town is the earlier it sees the sun in the morning, and the earlier it loses it again at night.

So happy Equilux everyone*!

* interestingly, the equilux does not occur on the same same day for everyone, it depends on your latitude. The closer you are to the equator the earlier the date of your equilux. For example the equilux in most US cities occurred yesterday, 17 March, and in cities near the equator there is never a day with exactly twelve hours between sunrise and sunset! Take Quito, the capital city of Ecuador (latitude 0 degrees 14 minutes south) for instance. The length of day there only ever varies between 12 hours and 6 minutes long and 12 hours and 8 minutes long!

  1. Simon
    May 9, 2011 at 08:29

    Hi Steve,

    I am trying to use an automated timer that has sunset and sunrise times built in (when you add your coordinates, in my case 37’48″S 144’57″E) to trigger something to turn on at Civil Twilight End.

    Is it possible to simply alter these location coordinates or would the relationship between the places shift over the seasons?

    Thanks in advance! Simon

    • May 13, 2011 at 12:01

      Hi Simon,

      You’re in Melbourne, right? Have a look at timeanddate.com, and enter “Melbourne” in the “Current Time” box, and then select the “Sun and Moon” tab, and then in the columns menu select “twilight/rise/set” which will show you all the times.

      During your midwinter, there is 29 minutes between sunset and the end of civil twilight. On your spring equinox there is a 26 minute gap. At midsummer a 31 minute gap. At autumn equinox a 26 minute gap.

      As you can see these times vary, and if you wanted you could go through each and every day of the year and see how the time varies, but it looks like it will be within 26 and 31 minutes regardless of the time of year. If you need it any more accurately then I’m afraid you’ll need to set each day separately!

  2. September 27, 2011 at 01:05

    Tomorrow is the autumnal equilux here in New Orleans. Having only recently become aware of this distinction from the equinox I have a question. I assume the proximity of equinox and equilux is not incidental. In other words, they are connected through basic celestial mechanics. Is that correct?

    • September 27, 2011 at 02:05

      That’s correct; the autumn equilux follows the autumn equinox after a few days (the autumn equinox this year fell on 23 Sep). This is due to the fact that between the summer solstice and the winter solstice the nights are lengthening every night. They lengthen from their shortest at the summer solstice, get *almost* to twelve hours long on the autumn equinox, get to *exactly* twelve hours long a few days later on the autumn equilux, then get to their longest on the winter solstice. They then shorten again until they are *exactly* twelve hours long on the spring equilux, a few days before the spring equinox… etc

  3. September 27, 2011 at 02:19

    Thanks. Just wanted to make sure it wasn’t some kind of cosmic coincidence.

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