Tweet
Fall Begins on Saturday: 4 Things to Know About the 2018 Autumnal Equinox
Sep 19, 2018 at 9:15 AM
While fall has been ongoing since Sept. 1 for meteorologists and climatologists, who define the seasons in groups of three equal months for ease of record-keeping, Saturday marks the official start of fall for the rest of us – astronomical fall – with the arrival of the autumnal equinox.
That means shorts and flip-flops are being retired for the year, jackets and sweatshirts are coming out of storage and everything is getting flavored with pumpkin spice as the crisp air of fall makes its annual return.
This year, the autumnal equinox is on Saturday, Sept. 22, at 9:54 p.m. EDT, and marks the end of summer and the beginning of fall.
Equinox seems like a complex term, but it's actually quite simple: 1. What is an Equinox?
Twice a year around March 20 or 21 and Sept. 22 or 23, the sun’s rays shine directly over the Earth’s equator. These days are known as the March equinox (vernal or spring equinox in the Northern Hemisphere) and the September equinox (autumnal equinox in the Northern Hemisphere).
2. What Happens During the Autumnal Equinox?
During the autumnal equinox, day and night are balanced to about 12 hours each all across the world. Instead of the Earth tilting away from or toward the sun, its axis of rotation becomes perpendicular to the line connecting the centers of the Earth and the sun.
This change in the Earth's tilt causes the change in seasons, with the Northern Hemisphere transitioning from the warmth of summer to the chill of winter as fall progresses. This process includes a shift in the overall location of the jet stream, which plays an important role in weather conditions.
Daylight in the Northern Hemisphere gradually becomes shorter up until the winter solstice in December. The opposite is true in the Southern Hemisphere, where daylight will gradually grow longer until that hemisphere's summer solstice in December.
The length of daylight is actually a bit longer than 12 hours during the autumnal equinox because of the way sunlight is measured.
Since sunrise is defined as the time when the first light directly from the sun ascends above the horizon and sunset is considered the time the last light directly from the sun descends below the horizon, there is roughly 12 hours and 5 to 15 minutes of daylight on the day of the equinox. The day that has exactly 12 hours of daylight in the Northern Hemisphere is 2 to 5 days past the autumnal equinox.
3. How Can I Tell the Equinox is Happening?
In addition to seeing the leaves change and advertisements for pumpkin-spice-flavored everything, the equinox brings about temperature changes. Fall is a transition season.
In the United States, fall is usually characterized by large variations in temperatures, as well as an increase in low-pressure systems bringing rain, thunderstorms or even snow across the country. Generally, after the fall equinox, temperatures continue to turn colder and snow becomes more common.
After a warm, humid September for most of the central and eastern states, a refreshing pattern change will bring a much more fall-like airmass to those regions later next week.
4. What Time Does Saturday's Autumnal Equinox Occur Where I Live?
Eastern Daylight Time: 9:54 p.m.
Central Daylight Time: 8:54 p.m.
Mountain Daylight Time: 7:54 p.m.
Mountain Standard Time (Arizona): 6:54 p.m.
Pacific Daylight Time: 6:54 p.m.
Alaska Daylight Time: 5:54 p.m.
Hawaii-Aleutian Standard Time: 3:54 p.m.
Sep 19, 2018 at 9:15 AM
While fall has been ongoing since Sept. 1 for meteorologists and climatologists, who define the seasons in groups of three equal months for ease of record-keeping, Saturday marks the official start of fall for the rest of us – astronomical fall – with the arrival of the autumnal equinox.
That means shorts and flip-flops are being retired for the year, jackets and sweatshirts are coming out of storage and everything is getting flavored with pumpkin spice as the crisp air of fall makes its annual return.
This year, the autumnal equinox is on Saturday, Sept. 22, at 9:54 p.m. EDT, and marks the end of summer and the beginning of fall.
Equinox seems like a complex term, but it's actually quite simple: 1. What is an Equinox?
Twice a year around March 20 or 21 and Sept. 22 or 23, the sun’s rays shine directly over the Earth’s equator. These days are known as the March equinox (vernal or spring equinox in the Northern Hemisphere) and the September equinox (autumnal equinox in the Northern Hemisphere).
2. What Happens During the Autumnal Equinox?
During the autumnal equinox, day and night are balanced to about 12 hours each all across the world. Instead of the Earth tilting away from or toward the sun, its axis of rotation becomes perpendicular to the line connecting the centers of the Earth and the sun.
This change in the Earth's tilt causes the change in seasons, with the Northern Hemisphere transitioning from the warmth of summer to the chill of winter as fall progresses. This process includes a shift in the overall location of the jet stream, which plays an important role in weather conditions.
Daylight in the Northern Hemisphere gradually becomes shorter up until the winter solstice in December. The opposite is true in the Southern Hemisphere, where daylight will gradually grow longer until that hemisphere's summer solstice in December.
The length of daylight is actually a bit longer than 12 hours during the autumnal equinox because of the way sunlight is measured.
Since sunrise is defined as the time when the first light directly from the sun ascends above the horizon and sunset is considered the time the last light directly from the sun descends below the horizon, there is roughly 12 hours and 5 to 15 minutes of daylight on the day of the equinox. The day that has exactly 12 hours of daylight in the Northern Hemisphere is 2 to 5 days past the autumnal equinox.
3. How Can I Tell the Equinox is Happening?
In addition to seeing the leaves change and advertisements for pumpkin-spice-flavored everything, the equinox brings about temperature changes. Fall is a transition season.
In the United States, fall is usually characterized by large variations in temperatures, as well as an increase in low-pressure systems bringing rain, thunderstorms or even snow across the country. Generally, after the fall equinox, temperatures continue to turn colder and snow becomes more common.
After a warm, humid September for most of the central and eastern states, a refreshing pattern change will bring a much more fall-like airmass to those regions later next week.
4. What Time Does Saturday's Autumnal Equinox Occur Where I Live?
Eastern Daylight Time: 9:54 p.m.
Central Daylight Time: 8:54 p.m.
Mountain Daylight Time: 7:54 p.m.
Mountain Standard Time (Arizona): 6:54 p.m.
Pacific Daylight Time: 6:54 p.m.
Alaska Daylight Time: 5:54 p.m.
Hawaii-Aleutian Standard Time: 3:54 p.m.
