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What Determines the Exact Date and Time of the Start of a Season on Earth?

-- David | August 22, 2020

Question:

I know what causes the change of the seasons. My question is, how do we know the exact date and time of this event?
Thanks

-- David

Answer:

The beginning of each season on Earth is defined by specific dates and times when the Sun crosses either the celestial equator, called an equinox, or when it reaches its lowest or highest point in the sky, called a solstice. Spring and fall begin on the spring and fall equinox, while summer and winter begin on the summer (Sun at its highest point in the sky) and winter (Sun at its lowest point in the sky) solstice. The dates and times of the equinoxes and solstices change from year-to-year due to the fact that our calendar has 365 days on it, when in fact it takes about 365.25 days for the Earth to make one complete orbit around the Sun.

-- Jeff Mangum

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