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Autumn’s equinox happens early Wednesday

WASHINGTON — Why hello fall! While the calendar may not officially mark the start of autumn just yet, temperatures tell a different story.

A lot of the daytime highs Monday will only top out in the 60s. The last time the D.C. region had daytime highs in the 60s was June 4, 2015. Temperatures will climb to back around normal this week, just in time for the autumnal equinox.

The autumnal equinox arrives precisely at 4:21 a.m. on Wednesday, Sept. 23. People celebrate this moment across the world because that is exactly the time when the sun passes directly over the equator. As you may recall, this happens twice a year — both in the spring and fall.

In Latin, the word “equinox” means “equal night” – “equi” meaning “equal” and “nox” meaning “night.” This signifies the equal parts of daylight and darkness. However, this is not always the case.

The sun will rise at 6:56 a.m. on Wednesday and will set at 7:04 p.m. This isn’t exactly equal. In fact, you will have to wait until Saturday, Sept. 26 to get the full equal light, equal night. The sunrise on Saturday is at 6:59 a.m. and the sunset will be at 6:59 p.m. EDT.

Diagram of the astronomical seasons courtesy of NWS. Autumnal Equinox: Incoming solar energy equal in both hemispheres. Winter Solstice: Incoming solar energy greatest in Southern Hemisphere. Vernal Equinox: Incoming energy equal in both hemispheres. Sumer Solstice: Incoming solar energy greatest in Northern Hemisphere. (Courtesy NWS)
Diagram of the astronomical seasons courtesy of NWS. Autumnal Equinox: Incoming solar energy equal in both hemispheres. Winter Solstice: Incoming solar energy greatest in Southern Hemisphere. Vernal Equinox: Incoming energy equal in both hemispheres. Sumer Solstice: Incoming solar energy greatest in Northern Hemisphere. (Courtesy NWS)

So what is going on here? Well, the atmosphere is to thank for this anomaly as well as the definition of sunrise and sunset. Sunrise occurs the moment the tip of the sun can be seen on the horizon, and sunset is the last minute the sun can be seen before it dips below the horizon. Also, keep in mind our atmosphere refracts, or bends, light, which makes it appear as if the sun is rising or setting earlier.

The true equinox occurs when the center of the sun’s disk crosses the celestial equator and this occurs at 4:21 a.m. EDT on Wednesday, Sept. 23. At the same time the equinox occurs in D.C., it occurs across the globe.

Temperatures on Wednesday will still be around 80 degrees, which is just slightly above the normal temperature for this time of year. However, you will notice that the hours of daylight will grow shorter up until the winter solstice, which begins at 11:49 p.m. EST on Dec. 21. This also will be the darkest day of the year, meaning the day with the least amount of daylight.

However, don’t put away those flip-flops just yet based on the calendar. According to the Climate Prediction Center, temperatures could be above average heading into the first week of October.

Here's the outlook for the next few days. (Courtesy NOAA)
Here’s the outlook for the next few days. (Courtesy NOAA)

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