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Equinox Sunset

21 Apr 2014, 07:01 UTC
Equinox Sunset
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The Vernal Equinox was close to a month ago. On that date (March 20, 2014) I captured a nice time-lapse of the sunset to demonstrate an effect you might not be aware of. I present it here for your edification. It shows the final 20 minutes before the Vernal Equinox sunset as seen from mid-Arizona. The speed-up factor is 48X.
The Equinox Sun rises exactly in the East, at azimuth 90°, and sets exactly in the West, at azimuth 270°. That much is commonly known. What you might not know is: The Equinox Sun’s path through the sky on its way up from sunrise, or on its way down to sunset, is inclined at an angle equal to your latitude. Of course, between sunset and sunrise, the Sun moves in various directions as it arcs across the sky. But during the first 30 minutes after sunrise, or the last 30 minutes before sunset, this rule holds quite nicely.
Here in Arizona, at latitude 34° North, we see that sunset path inclined at an angle of 34° to the vertical. That’s the yellow line in the animation above. Run the animation now, and watch the Sun follow that line until it ...

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