Clusters of redbud blossoms cover the tree’s branches in the early spring, before the leaves begin to unfold.
Credit: © Thinkstock

Spring has sprung! Today, Monday, March 20th, is the vernal equinox. The equinox is the official marker of the spring season in the Northern Hemisphere. The equinox occurs when the sun is directly above Earth’s equator. When the sun is in this position, all places on Earth receive approximately 12 hours of sunlight. The term equinox comes from a Latin word meaning equal night.

Many people in the United States are welcoming spring with piles of snow outside their front door! Unseasonal and abnormal storms have hit California and the northeast United States. Heavy rain, snow, hail, and even tornadoes have hit California in the last two months. The flooding has broken levees in some communities in northern California, raising fears of even more damage. A nor’easter hit New England on Tuesday, March 14th, after an unusually quiet winter, dropping nearly 28 inches (71 centimeters) of snow in Vermont and Massachusetts. A nor’easter is a powerful storm coming from winds going northeast that produces a lot of precipitation. Many people throughout the United States are keeping their snow shovels, boots, and parkas out for a few more weeks!

A snowstorm in the Boston area left two feet of snow. Credit: AP Photo

The equinoxes occur on March 19, 20, or 21 and on September 22 or 23. In the Northern Hemisphere, the March equinox marks the start of spring and is often called the vernal equinox. The position of the vernal equinox is called the first point of Aries. The word vernal means of spring. The September equinox marks the beginning of autumn and is called the autumnal equinox. The seasons are reversed in the Southern Hemisphere.

The time interval from the March equinox to the September equinox is longer than that between the September equinox and the next March equinox by several days. This time difference results from the earth’s elliptical (oval-shaped) orbit around the sun. The earth moves faster in its orbit when it is closer to the sun. The distance between the earth and the sun is shortest in January. Therefore, the earth completes the semicircle from the September equinox to the March equinox faster than it does the opposite semicircle.

The equinoxes are the two moments of the year when the sun is directly above the equator. As Earth moves in its orbit around the sun, the position of the sun changes in relation to the equator, as shown by the dotted lines in this diagram. The sun appears north of the equator between the March equinox and the September equinox. It is south of the equator between the September equinox and the next March equinox. Credit: WORLD BOOK diagram

Historically, the year began with spring in many cultures. Evidence of this practice in ancient Rome remains part of the modern calendar. Counting March instead of January as the first month of the year, we find that September, October, November, and December are the seventh, eighth, ninth, and tenth months. The prefixes sept-, oct-, nov-, and dec- come from the Latin words for 7, 8, 9, and 10.

Spring looks different around the world. The Northern Hemisphere has spring weather from late March through May. In the Southern Hemisphere, spring weather begins in September and lasts through November. The number of daylight hours increases during spring, particularly in the polar regions, and the temperature rises. Nature awakens in spring. Flowers bloom, and hibernating animals leave their winter sleeping places. Many cultures have festivals that celebrate the arrival of spring. Find your own way to celebrate spring this year. Spring is a new beginning, enjoy the flowers, longer days, and warmer weather!

A Connecticut village in autumn is ablaze with the brilliant colors of turning leaves. Every year, many vacationers visit the state to enjoy its scenic countryside and to explore its many picturesque villages and historic sites.
Credit: © Corbis Bridge/Alamy Images

Fall means pumpkins, colorful leaves, and crisper weather. It also means the end of summer. What causes the seasons to change? The four seasons result from the tilt of Earth’s axis of rotation and the planet’s motion around the sun. The axis slants at an angle of 23 degrees 27 minutes in relation to the plane of Earth’s orbit. As a result, Earth’s Northern and Southern hemispheres tilt toward or away from the sun during different times of the year. Some people mistakenly believe that seasons result from Earth moving closer to or farther from the sun at different times of the year. But Earth orbits at nearly the same distance from the sun throughout the year. The small changes in distance that do occur have little effect on Earth’s weather.

Today, at 9:03 p.m. Eastern Time, the autumnal equinox marks the beginning of autumn in the Northern Hemisphere. In the Southern Hemisphere, where the seasons are reversed, the event is called the vernal equinox and marks the start of spring. The word vernal means of spring. An equinox is either of the two moments each year (the other is in March, again changing the seasons) when the sun is directly above Earth’s equator. On the days of the equinoxes, all places on Earth receive approximately 12 hours of sunlight. Today, the sun rose at 6:43 a.m. Eastern Time and will set at 6:53 p.m.—a total of 12 hours and 10 minutes of daylight. The term equinox comes from a Latin word meaning equal night. The equinoxes occur at different times of day each year on March 19, 20, or 21 and on September 22 or 23.

The time interval from the March equinox to the September equinox is longer than that between the September equinox and the next March equinox. This time difference results from the Earth’s elliptical (oval-shaped) orbit around the sun. Our planet moves faster in its orbit when it is closer to the sun. The distance between the Earth and the sun is shortest in January. Therefore, the Earth completes the semicircle from the September equinox to the March equinox faster than it does the opposite semicircle.

Astronomers also use the term equinox for either of two imaginary points where the sun’s apparent path among the stars crosses the celestial equator. The celestial equator is an imaginary line through the sky directly over the equator.

After the autumnal equinox, the weather cools and nights become longer than days, and days continue to shorten until the winter solstice. The weather then warms and daylight begins its recovery toward the summer solstice in June. The winter solstice is technically the shortest day of the year, and the day of the summer solstice enjoys the most sunlight.

Tulips are colorful garden flowers that bloom in the spring. Tulip leaves and the flower stem grow directly out of a bulb.
Credit: Derek Fell

Spring has sprung! Sunday, March 20th, was the vernal equinox, the official marker of the spring season in the Northern Hemisphere. The equinox occurs when the sun is directly above Earth’s equator. When the sun is in this position, all places on Earth receive approximately 12 hours of sunlight. The term equinox comes from a Latin word meaning equal night.

The equinoxes occur on March 19, 20, or 21 and on September 22 or 23. In the Northern Hemisphere, the March equinox marks the start of spring and is often called the vernal equinox. The position of the vernal equinox is called the first point of Aries. The word vernal means of spring. The September equinox marks the beginning of autumn and is called the autumnal equinox. The seasons are reversed in the Southern Hemisphere.

The equinoxes are the two moments of the year when the sun is directly above the equator. As Earth moves in its orbit around the sun, the position of the sun changes in relation to the equator, as shown by the dotted lines in this diagram. The sun appears north of the equator between the March equinox and the September equinox. It is south of the equator between the September equinox and the next March equinox.

The time interval from the March equinox to the September equinox is longer than that between the September equinox and the next March equinox by several days. This time difference results from the earth’s elliptical (oval-shaped) orbit around the sun. The earth moves faster in its orbit when it is closer to the sun. The distance between the earth and the sun is shortest in January. Therefore, the earth completes the semicircle from the September equinox to the March equinox faster than it does the opposite semicircle.

Historically, the year began with spring in many cultures. Evidence of this practice in ancient Rome remains part of the modern calendar. Counting March instead of January as the first month of the year, we find that September, October, November, and December are the seventh, eighth, ninth, and tenth months. The prefixes sept-, oct-, nov-, and dec- come from the Latin words for 7, 8, 9, and 10.

Spring looks different around the world. The Northern Hemisphere has spring weather from late March through May. In the Southern Hemisphere, spring weather begins in September and lasts through November. The number of daylight hours increases during spring, particularly in the polar regions, and the temperature rises. Nature awakens in spring. Flowers bloom, and hibernating animals leave their winter sleeping places. Many cultures have festivals that celebrate the arrival of spring. Find your own way to celebrate spring this year. Spring is a new beginning, enjoy the flowers, longer days, and warmer weather!

September 22, 2017

Today, at 4:02 p.m. Eastern Time, the autumnal equinox marks the beginning of autumn in the Northern Hemisphere. In the Southern Hemisphere, where the seasons are reversed, the event is called the vernal equinox and marks the start of spring. The word vernal means of spring. An equinox is either of the two moments each year (the other is in March, again changing the seasons) when the sun is directly above Earth’s equator. On the days of the equinoxes, all places on Earth receive approximately 12 hours of sunlight. Today, the sun rose at 6:43 a.m. Eastern Time and will set at 6:52 p.m.—a total of 12 hours and 9 minutes of daylight. The term equinox comes from a Latin word meaning equal night. The equinoxes occur at different times of day each year on March 19, 20, or 21 and on September 22 or 23.

The equinoxes are the two moments of the year when the sun is directly above the equator. As Earth moves in its orbit around the sun, the position of the sun changes in relation to the equator, as shown by the dotted lines in this diagram. The sun appears north of the equator between the March equinox and the September equinox. It is south of the equator between the September equinox and the next March equinox. Credit: WORLD BOOK diagram

The time interval from the March equinox to the September equinox is longer than that between the September equinox and the next March equinox. This time difference results from the Earth’s elliptical (oval-shaped) orbit around the sun. Our planet moves faster in its orbit when it is closer to the sun. The distance between the Earth and the sun is shortest in January. Therefore, the Earth completes the semicircle from the September equinox to the March equinox faster than it does the opposite semicircle.

Astronomers also use the term equinox for either of two imaginary points where the sun’s apparent path among the stars crosses the celestial equator. The celestial equator is an imaginary line through the sky directly over the equator.

After the autumnal equinox, the weather cools and nights become longer than days, and days continue to shorten until the winter solstice. The weather then warms and daylight begins its recovery toward the summer solstice in June. The winter solstice is technically the shortest day of the year, and the day of the summer solstice enjoys the most sunlight.

March 20, 2012

The March equinox has marked the official start of spring in the Northern Hemisphere and of autumn in the Southern Hemisphere. At the March equinox, the sun is directly above the Earth’s equator. On the days of the equinox, all places on Earth receive approximately 12 hours of sunlight, though the exact amount of daylight in different locations varies by as much as several minutes. All places also have approximately 12 hours of darkness.

The equinox officially occurred at 5:14 Coordinated Universal Time (UTC) on Tuesday, March 20, at the prime meridian at the Royal Greenwich Observatory in Greenwich, England. In the United States, 5:14 UTC was 10:14 p.m. in Los Angeles (Pacific Standard Time) on Monday, March 19, and 1:14 a.m. in New York City (Eastern Daylight Time) on Tuesday. In Sydney, Australia, the March equinox began at 4:14 p.m. (Australian Eastern Daylight Time) on March 20.

The March equinox is one of two equinoxes that take place as Earth completes a full orbit of the sun. The March equinox occurs on March 19, 20, or 21. The September equinox takes place on September 22 or 23. This year’s spring equinox is the earliest since 1896. As a result, winter was only 88.994 days long.

The equinoxes are the two moments of the year when the sun is directly above the equator. As Earth moves in its orbit around the sun, the position of the sun changes in relation to the equator, as shown by the dotted lines in this diagram. (World Book diagram)

The positions of the two equinoctial points do not remain the same from year to year. They shift westward extremely slowly–about 1 degree every 70 years. This gradual movement of the points, called the precession of the equinoxes, is caused by a slight change in the direction of Earth’s axis of rotation. The change results mainly from the gravitational pull of the moon and the sun on Earth’s equatorial bulge.

In the United States, the start of spring has been accompanied by record high temperatures throughout much of the nation. On March 14, 400 locations around the United States reported record highs. Even the 68 °F (20 °C) temperature at Duluth, Minnesota, which was far below the 80 °F (27 °C) reported in Miami, Houston, and Chicago, was 35 Fahrenheit degrees (19 Centigrade degrees) above average.

Additional World Book articles:

• Reading the Sky: Early Places of Astronomy (a Special Report)
• Astronomy
• Season