Fall equinox arriving soon

Weather

Although abnormal warmth continues to dominate our weather, we are rapidly approaching the end of the summer season.

Pause button: Technically, as meteorologists, we think in terms of meteorological seasons, which are timed around temperature changes, not the sun’s position in the sky like astronomical seasons.

In weather terms, fall started back on September 1st.

Okay, unpause again.

Astronomical autumn arrives on Monday at 2:50 AM with the autumnal (or fall) equinox. That’s when the Earth’s tilt results in equal sunlight for both the Northern & Southern Hemispheres.

The sun will be up for 12 hours & 7 minutes on Monday.

By December 21st, when the Northern Hemisphere reaches its maximum tilt away from the sun, our day length drops all the way to 9 hours & 10 minutes.

If you’re an morning or evening commuter, you’ve probably noticed the approaching equinox while driving.

The changing sun angle is what causes you to be blinded whenever you’re on an east/west road this time of year.

Day is still longer than night?

Perhaps you noticed earlier that even on the equinox (Latin for “equal night), there are still more than 12 hours of daylight.

There are two reasons for this.

First, sunrise & sunset are technically when the top of the sun crosses the horizon. That means sunrise really happens before the whole sun is visible, and sunset occurs after most of the sun has gone down.

Second, due to the Earth’s atmosphere, we can actually see the sun before it rises and after it sets.

Early & late in the day, sunlight is noticeably refracted (bent) by atmospheric gases — just like a prism bending light into a rainbow — so we see red, orange, & purple colors in the sky, rather than just blue.

That same refraction means even when the curve of the Earth hides the sun, the light is being bent around the earth, making our star visible.

Long story short, that’s why there technically isn’t ever exactly 12 hours of day & 12 hours of night.

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