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The Evenings are Drawing Out December 14, 2009

Posted by mwidlake in Perceptions.
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Today, sunset was later than yesterday. In London it was 15:51 and 50ish seconds. Tomorrow, the sun will resolutely stay in the sky until 15:52 {and a few seconds}. The days are drawing out at last.

English Sunset by Angie Tianshi

But it is not the shortest day of the year {I should say daytime really, all days are the same length give or take odd leap-seconds)

What is, I hear you all cry?

The shortest day is December 21st

{or December 22nd, depending on how long ago the last leap-year was}. And you would be right, the date with the shortest period of daylight is the the 21st/22nd December. And everyone knows that the the shortest day will also be the day where the sun sets earliest, it makes sense.

Except it does not quite work like that.

We probably all remember from our school days that the earth goes around the sun at an angle from the “vertical”, if vertical is taken as at 90 degrees to the circle the planet takes as it spins around the sun. Think of it like an old man sitting in a rocking chair. He is rocked back in his chair, head pointing back away from the sun in the Northern Hemisphere’s winter and feet pointing slightly towards the sun. Come Midsummers day, he has rocked forward, head pointing towards the sun for the Northern Hemisphere summer. One rocking motion takes a year.

Well, old earth is also slumped slightly to one side in his chair. This results in a slight skew on when sunset starts drawing out and when sunrise starts drawing in. Sunrise will continue to get later until we hit the New Year (Western New Year, not Chinese :-) ). It just so happens that sunset gets later at a slower rate than sunrise gets later until the 21st, when we hit the Shortest Day.

To be fair, I missed the boat slightly, the point at which the evenings started to stretch out was actually the 13th or 14th December but I did not have time to blog until today.

The below tables help make this situation clearer, I include one for the UK and one for Australia. The joly nice site it links to allows you to change the location to wherever you are in the world (well, the nearest Capital).

Table of sunrise/sunset times for London

Table of surise/sunset for Sydney, Australia

What has this to do with Oracle, Performance and VLDBs? Nothing much, except to highlight that the obvious is not always correct, just as it is with Databases and IT in general.

I’ll finish with a sunset picture from Auz. Ahhhh.

Outback sunset from ospoz.wordpress.com

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Comments»

1. Where is Sun? « Martin Widlake's Yet Another Oracle Blog - January 3, 2011

[...] furthest/closest to the sun does not match the longest/shortest day. As some of you may remember, I explain about the oddities of the shortest day not matching when the nights start drawing out about this time last year. It is because as we spin around our own pole and around the sun, things [...]


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