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Good Gardening: Sun Shift


Hi All, Master Gardener, and amateur astronomer John Fischer here with KLCC's Good Gardening.

We're going to leave our plants out of the discussion this month, and look at some odd things the sun is doing instead.
Most people know that December 21st is the shortest day of the year, but careful observers will tell you that the earliest sunset of the year occurs only 3 days from now, and that the latest sunrise won't happen until January 2nd.

Yes, the shortest day is the 21st. 8 hours and 56 minutes between sunrise and sunset. But if you really miss the light in the evening, starting December 10th the sun will set a little later, and we will have 4 more minutes of daylight in the evening by the 21st. Early risers on the other hand will have to wait until the 3rd of January to see more morning light.

The reason for this shift is our insistence on each day being the same length. Because the earth's orbit is an ellipse, not a circle, we are closer to the sun now, and therefore moving through space faster. Solar noon is the time the sun is due south and highest in the sky. The time between solar noon day to day is not exactly 24 hours. It changes in relation to our distance from the sun. If the earth's orbit was a more flattened ellipse, the effect would be even greater.

The small shift in sunrise and sunset times is an artifact of our adherence to mechanical time, not solar time. This concept of shifting sunrise and sunset is difficult to grasp with words alone. Do some internet research, or go to this link to get a better visual explanation.

I'll be back talking plants next month, and we'll have a little more light to get things done outside - in the evenings.

I'm John Fischer with KLCC's Good Gardening.

Copyright 2021, KLCC

John Fischer is a Master Gardener and Master Recycler and the host of KLCC's Good Gardening and Living Less Unsustainably.
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