The Mystery of the Missing Sunlight
The astronomical reason daylight decreases in autumn: Earth's 23.5° axial tilt, its orbit around the Sun, and how changing sunlight creates the seasons.
The sun is taking its time getting up, the evenings are arriving earlier, and there's a chill in the air. Later sunrises, earlier sunsets, and cooler temperatures are all signs of the turning of the year. As the days grow shorter, we're reminded that change is part of the rhythm of life. What can we learn from this quieter season? Let's take a closer look at the science and wonder behind our shortening days.
Our days are getting shorter right now because the Earth’s rotation axis is tilted by 23.5 degrees with respect to the sun. For this reason, the sun directly faces different parts of our planet at different times of the year.
As shown in the picture below, the sun directly faces the Tropic of Capricorn in the southern hemisphere at the time of the winter solstice, which occurs on December 21st. It directly faces the equator at the time of the spring equinox, which occurs on or about March 20th. It directly faces the Tropic of Cancer in the northern hemisphere at the time of the summer solstice, which occurs on June 21st and again directly faces the equator at the time of the fall equinox, which occurs on or about September 22nd.
Because Michigan is in the northern hemisphere, our days are longest at the time of the summer solstice on June 21st, when the sun directly faces the Tropic of Cancer. On that date, daytime lasts 15 hours and 13 minutes in southern Michigan and nearly 16 hours in the northernmost part of the Upper Peninsula.
After the summer solstice, our days start getting shorter. They are the shortest at the time of the winter solstice on December 21st, when the sun directly faces the Tropic of Capricorn. On that date, daytime lasts only 9 hours and 6 minutes in the southern part of the state and 8 hours and 44 minutes in the northernmost Upper Peninsula.
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From the long, lingering light of June to the early darkness of December, Michigan's days follow a predictable seasonal rhythm. As the sun rises later and sets earlier, we're reminded that the turning of the year is always underway, even when the changes seem small. Check out this YouTube video for a closer look at what's happening.