HOUSTON – Ahhhh, the first day of fall. As the leaves change color, temperatures drop and we can order a pumpkin latte to warm our hands and hearts… But not in Houston. Houston is expecting highs of 80 degrees over the next week. This begs the question, why does fall officially start on Sunday?

It’s important that we understand what the first day of fall really means. The autumn equinox has nothing to do with temperatures. It has everything to do with the relationship between the Earth and the Sun.

On Sunday morning, September 22nd, the sun’s direct rays will hit the equator at 7:44 a.m. This is a time that occurs worldwide when the sun is directly over the equator. This is the autumn equinox. The word equinox comes from the Latin word for “equal night.” In Houston, we don’t have a perfect 12 hours of daylight and 12 hours of night on this day, but it’s pretty close. Sunrise is at 7:10 a.m. and sunset is at 7:17 a.m. The cool thing about Sunday is that the sun rises in the east and sets exactly in the west.

The sun is not a point in the sky, but a disk. The scientific definition of sunrise, as established by the United States Naval Observatory, is when the top of the sun is first visible (at sea level). Similarly, the definition of sunset is when the top of the sun falls below the horizon. This difference gives us 2-3 more minutes of sunlight each day. The atmosphere also refracts or bends sunlight, making the sun appear on the horizon even though it is still physically below the horizon.

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Equilux day is the day when day and night are most likely to be equal in length. In Houston this year, that day is September 26th, when the sun is above the horizon for 11 hours, 59 minutes and 56 seconds.

On Thursday we hit a new record high of 98° in the heat of the day. The previous record was 97° in 1995. So will it ever get cooler? YES. Fall brings shorter days. In a month or two, our daylight hours will be an hour shorter. Less sun means cooler temperatures.

And we’re also in the season where we get our first real cold front. A front that will bring temperatures into the 20s and drop humidity. It’s not in the 10-day forecast yet, but it will arrive here sometime in October.