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The end is near

No, not the end of the Earth (yet again) but the end of all this darkness. Unless of course you read this blog in the summer and then I have some bad news for you. 

Sure, we know that we get a few extra seconds of daylight each day after the winter solstice but it’s generally too little to notice from one day to the next. So I looked at the Lighting Times report for the default facility in STK to see the daily change here at AGI HQ. The graphs below show both the daily duration in hours and the change from one day to the next in seconds. 

So we (at AGI) are currently gaining about one minute a day which adds up quickly. Just for giggles, I wanted to see how this compares to the extremes close to the equator and close to the poles. Using Singapore for the equator example mostly gave the expected results of very small changes in daylight throughout the year. Turns out that there will be a solar eclipse in the summer though, so that’s where the odd spike is coming from. 

For the polar extreme, I went with Svalbard. Other than the solar eclipse in Singapore, this was initially the most surprising result for me. Yes, I expected a very quick change since we had to go from complete darkness to 24-hour sunlight in about 2 months but I expected a sinusoidal shape like the other graphs. 

Turns out that during the last few days of no direct sunlight, the Sun stays just barely below the horizon for quite a while. Once it actually reaches a positive elevation, it stays positive for some time. The graph below shows sun elevation for the days just as the Sun passes over the horizon. The yellow area indicates elevations of full sunlight, the orange region is penumbra, and the green region umbra. Note that I removed terrain for all this to get cleaner graphs.

Here is the Matlab script I used to generate all these graphs: DaylightSingleSite.m

Author

Jens Ramrath


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