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I calculated some predictions of what dates the sun should set behind each peak. The red numbers are the precise bearing and distances from my balcony. I also calculated the parallel latitude point in Seattle for each peak, that is the point in the city directly due east of the peak. It is the point from where you can see, on the equinoxes, the sun setbehind that peak.
The full visible front range is 21.5 miles south to north from the peak of Mt Ellinor to the peak of Mt Townsend. It runs parallel to a line from Boeing Field to Paine Field.
There is a rumor that the sun sets between The Brothers on the equinoxes which turns out to be true, but only if you are in the meadow on the bluff in Discovery Park.
Surprisingly (to me at least) the parallax is such that the sunset peak changes as you move just a short distance in the city. To demonstrate the that difference i marked the sunset peak from two different locations on the same day.
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Here's a line graph of the positions of the peaks sorted by bearing from my home.
And here's a latitude-longitude XY graph of the actual positions
of the peaks with some sunset dates stuck in.
I also did a lot of experiments with timing.
What one defines as sunset differs among people. The most exciting and romantic colors are 5 to 30 minutes after the sun winks out, so many people define that time of day. Some people like the actual disc movement and others the anticipation and so define sunset as the time BEFORE the sun disappears. Scientifically the sunset is the moment the last bit of the disc of the sun winks out.
Over several months i consistently timed the period from first contact to last wink out as 3 min 55 seconds. We could calculate an exact number of seconds from the size of the sun, distance away and speed the earth is turning, but 4 minutes is close enough to work with.
As we can see above, the Olympic Mountains create wonderful sunsets, but they do effect the moment the sunset happens. If we figure they are 2000 m high and 60 km away that should be just over 3 degrees, and since the sun is 1.7 degrees across that's 2 sun disks which means 8 minutes. And my testing consistently found that moment of the sun's disk's first contact is consistently 12 minutes before the published sunset time. Four minutes for the disk to slip behind the mountain top, plus 2 sun disks behind the mountains to reach the theoretical exact horizon is 4+8= 12.
So if you want to see first contact, watching the sunset over the Olympic Mountains from Seattle, plan to be in place a bit more than 12 minutes before the published time.
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