Why southern Colorado sunsets are already getting later

COLORADO (KOAA) — While the winter solstice, the shortest day of the year, is still a couple weeks away, Southern Colorado has already passed its earliest sunset of the year.

The earliest sunset occurred on December 7, when the sun set at 4:37 p.m. By December 21, the winter solstice, sunset will have moved slightly later to 4:40 p.m. By New Year's Eve, sunset will occur at 4:47 p.m.

This phenomenon happens because of the way the sun moves through the sky. Solar noon occurs when the sun is highest in the sky, but that's not the same as noon on your watch.

Have you ever seen a sundial? Sundials measure time based on the position of the sun in the sky. Light hits the dial at a certain angle, and at solar noon, when the sun is highest in the sky, the dial has no shadow.

But solar noon is not the same thing as noon on your watch. At some parts of the year, that sundial runs faster than your watch. At other times, it runs slower.

There are two reasons why this happens. First, Earth's orbit isn't a perfect circle — it's slightly oval shaped. Think of it like a race track: Earth gets closer to the sun in December and pushes the gas pedal, speeding up its orbit a bit.

Second, Earth is tilted on its axis, which is why we have seasons. That tilt, plus Earth speeding up in its orbit, changes when solar noon occurs.

The sun moves along a tilted plane in the sky because Earth is tilted on its axis. It's called the ecliptic. Each day, the sun moves about 1 degree along this line. Fun fact: that's why compasses have 360 degrees.

Around the equinoxes, most of the daily motion is left-right to the east. Around the solstices, most of the motion is up-down. Without getting too complicated, when the sun moves mostly east, it takes less than 24 hours for the sun to get back to solar noon the next day.

In December, solar noon gets later each day by about 20 to 30 seconds. Your watch doesn't do that of course, noon is always noon. Since solar time is getting later while your watch stays the same, sunsets get later after December 6. But so do sunrises.

Sunrises in early December occur around 7 a.m. January 5 marks the latest sunrise at 7:18 a.m.

The main takeaway is that the shape of Earth's orbit and its tilt mean Southern Colorado is already gaining daylight in the evenings. Some news to really brighten the end of your day.

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