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!

Brace yourself for six more weeks of winter.

Today, February 2, is Groundhog Day, a United States tradition that supposedly predicts when spring will arrive. According to legend, the groundhog, also called the woodchuck, awakens from winter sleep on February 2 and emerges from its burrow. Winter sleep is a state of reduced activity similar to hibernation. If the sun is shining that day and the groundhog sees its shadow, it will be scared back into its den, and there will be six more weeks of winter.  But if it is cloudy and the groundhog does not see its shadow, it will come out, and spring will arrive soon. The groundhog belongs to a group of rodents, or gnawing mammals, known as marmots. Groundhogs live in parts of Canada and the United States.

This morning, when the groundhog was awakened, it saw its shadow. It then scampered into its den and began preparing for a several more weeks of cold. Maybe it made a cup of hot cocoa!

The groundhog, also called a woodchuck, is a burrowing rodent with a chunky body. Credit: © Leonard Lee Rue III, Tom Stack & Assoc.

For hundreds of years, European farmers had similar traditions that involved bears, badgers, and other animals. Germans who settled in Pennsylvania brought the custom to America. The groundhog, which is plentiful in the eastern and Midwestern United States, became linked with the custom. Today, Groundhog Day is treated largely as a joke. But the custom is partly based on ancient and traditional weather signs. People have long looked to the awakening of hibernating animals as one of the first signs of spring.

In Punxsutawney, Pennsylvania, a groundhog named Phil has been the nation’s official spring prognosticator (predictor) since 1887. The celebration has become a media event, and it draws a crowd of thousands. (This year, the celebration will be a virtual affair—part of ongoing efforts to prevent the spread of COVID-19.) According to the Punxsutawney Groundhog Club, Phil’s full name is “Punxsutawney Phil, Seer of Seers, Sage of Sages, Prognosticator of Prognosticators and Weather Prophet Extraordinary.” Except for Groundhog Day and other special occasions, Phil lives in a climate-controlled habitat at the Punxsutawney Library. Phil starred alongside Bill Murray in the 1993 comedy film Groundhog Day.

May 20, 2019

What do you call an earthquake on Mars? A marsquake! For the first time, scientists working with the United States National Aeronautics and Space Administration (NASA) think they have detected an actual temblor on the red planet.

Scientists think they have detected marsquakes on Mars, the fourth planet from the sun. Credit: NASA/JPL/Malin Space Science Systems

At the end of 2018, NASA’s InSight probe deployed a specially-built seismometer called Seismic Experiment for Interior Structure (SEIS) to the surface of Mars. (InSight is short for Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport. InSight launched from Earth in May 2018 and landed on Mars in late November.) On April 6, 2019, SEIS picked up faint vibrations that were not caused by wind or the movement of InSight’s robotic arm. The signal was faint, with a low-level magnitude between 1 and 2 on the Richter scale. On Earth, such a weak quake would go unnoticed. On Mars, however, InSight was there to feel it.

Mars is the third body on which humans have recorded seismic activity, after Earth and the moon. On Earth, quakes are caused by the bending and grinding of huge tectonic plates, which float on layers of soft rock and magma and hold the planet’s oceans and continents. Mars does not have tectonic plates. Marsquakes are likely caused by the shrinking of the planet’s interior, which itself is caused by the slow cooling of its core.

NASA’s InSight probe has been studying the surface of Mars since late November 2018. Credit: NASA/JPL-Caltech

While detecting marsquakes is exciting, readings from SEIS might also shed light on the structure of the red planet. Scientists have reason to think that Mars, like Earth, has an interior composed of a rocky outer crust, a soft mantle, a liquid outer core, and a solid inner core. But they do not know how thick each of the layers are. Seismic waves change direction slightly when passing through core layers. If scientists know the source of the seismic waves, they can get an idea of the kinds and sizes of layers the waves had to pass through to reach the seismometer. Scientists can then create a more accurate map of the Martian interior and gain insight into the structure of all rocky planets—including those in our solar system and those orbiting stars millions of light-years away.

InSight has many instruments in addition to SEIS. The probe also serves as the only weather station on another planet. Sensors track the brisk wind gusts, low pressures, and frigid temperatures of Elysium Planitia, a vast plain near the Martian equator. On May 11, the temperature climbed to -4 °F (-20 °C) during the day, but plummeted to -148 °F (-100 °C) during the Martian night. Wind speeds topped out at 32 miles (51 kilometers) per hour.

October 11, 2017

On Monday, October 9, multiple wildfires swept across northern California, destroying some 2,000 homes and other buildings, killing 21 people and displacing tens of thousands of others. California Governor Jerry Brown declared states of emergency in Butte, Lake, Mendocino, Napa, Nevada, Sonoma, and Yuba counties, where the destruction is worst. Dozens of people remain missing as the fires continue to burn.

Firefighters hose the flames of a burning home in the Napa wine region of California late on Oct. 9, 2017. Credit: © Josh Edelson, AFP/Getty Images

Unusually hot and dry weather this summer has created ideal conditions for wildfires across northern California. At least 15 separate blazes broke out over the weekend, and strong winds whipped the flames across some 114 square miles (295 square kilometers). Napa and Sonoma counties, the heart of California’s wine country, were hardest hit. The status of the grape harvest remains unclear, but damage from fire and smoke is almost certainly widespread. Fires devastated parts of the city of Santa Rosa, where entire neighborhoods have been left in ashes and cinders.

Skies from San Francisco to Sacramento to Eureka remain choked with smoke and haze, and an orange glow illuminates the night. Numerous roads, schools, and business are closed, and several hospitals in the fire zone have been evacuated. Thousands of firefighters and numerous firefighting aircraft—including the massive Global SuperTanker (a converted Boeing 747 airliner)—are battling the blazes. Amy Head, the fire captain spokesperson for Cal Fire, the state agency responsible for fire protection, said the fires were probably linked to a warming climate. “It has been hotter, it has been drier, our fire seasons have been longer, fires are burning more intensely, which is a direct correlation to the climate changing,” she said.

Another state of emergency was declared on Monday in southern California’s Orange County, where a wildfire destroyed several homes in the affluent Anaheim Hills neighborhood and forced the evacuation of hundreds of residents.

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.

August 30, 2017

Late last Friday night, on August 25, the deluge of Hurricane Harvey began soaking the central coast of Texas in the southern United States. Since then, the storm has continued to dump record rains, causing unprecedented flooding that has displaced some 30,000 people. More than 4 feet (1.2 meters) of rain has saturated the Houston area, submerging low-lying areas and swelling reservoirs to near-breaking points. As Harvey hovers and continues to dump torrential rains, the U.S. National Weather Service warns of “catastrophic” and “life threatening” flooding in southeastern Texas and southwestern Louisiana. As of today, 30 people have died in storm-related incidents.

On Aug. 27, 2017, members of the Texas National Guard evacuate Houston residents stranded by Hurricane Harvey’s record flooding. Credit: Lt. Zachary West, Army National Guard

Harvey’s floodwaters have affected 50 counties in Texas, and some 4,000 troops from the Texas National Guard have been deployed—along with thousands of police, firefighters, and other emergency responders—to help the storm’s many victims. Many civilian volunteers are helping, too, using their own boats, food, and other supplies. Numerous people and pets have been rescued by boat, high-water vehicles, and helicopter from automobiles, trees, homes, and rooftops. Hundreds of roads are blocked by high water, and Houston’s airports, schools, and office buildings remain closed. Storm damage is expected to top $20 billion, and repairs and reconstruction after the storm could take years. Some 450,000 people are expected to seek federal disaster assistance. Harvey is the strongest storm to hit Texas since Hurricane Carla in 1961.

On Aug. 24, 2017, Hurricane Harvey strengthens over the Gulf of Mexico prior to hitting the Texas coast late on August 25. Credit: NOAA/NASA GOES Project

Harvey’s pockets of tornadolike winds have caused some damage, but the storm’s winds—which have lessened enough for Harvey to be downgraded to a tropical storm—have not been the problem. Harvey’s great destructive force has been its rain generation. Very slow moving, Harvey has lingered over the Texas coast and the Gulf of Mexico, turning out multiple thunderstorms from a bottomless water supply. Torrential rains have hit coastal areas for days on end, and flooding and storm surges have not reached their peak potential. The worst may be yet to come before the storm crawls northeast and weakens over land in the coming days.

Harvey formed as a cluster of thunderstorms over the Atlantic Ocean before hitting the island of Barbados as a tropical storm on August 18. The storm fragmented as it crossed Mexico’s Yucatán Peninsula, but it redeveloped and gained strength over the Bay of Campeche. Water temperatures there and in the entire Gulf of Mexico are well above average, and storms like Harvey feed off those warm waters. An expansion of the subtropical high pressure belt gave Harvey a clear and gentle upper atmosphere in which to grow, and the storm coiled and flexed into a hurricane as it neared the Texas coast. The warmer waters and expansion of high pressure areas—as well as a superabundance of moisture in the air—are ripe conditions for hurricane creation. They are also consistent with the effects of anthropogenic (human-caused) climate change. The United Nations World Meteorological Organization linked Harvey’s enormous rainfall with climate change.

January 23, 2017

Tornadoes swept through parts of the southeastern United States over the weekend, killing 20 people and injuring and displacing many others. Most of the deaths—15 of them—occurred in the state of Georgia. Four others were killed in Mississippi and one person died in northern Florida. The tornadoes erupted from a violent storm front that also hit the states of Louisiana, Alabama, and South Carolina.

This satellite image shows the strong storm front over the southeastern United States on Jan. 22, 2017. The storm killed 20 people in 3 different states. Credit: NASA/NOAA/GOES

The storm hit first in Louisiana early on Saturday, January 21, as severe weather damaged homes and caused injuries around the north-central city of Natchitoches. The storm then roared into southern Mississippi, where predawn tornadoes killed four people in the city of Hattiesburg.

Tornadoes touched down as the storm passed through Alabama, but the full wrath of the storm hit southern Georgia on Sunday, January 22. Tornadoes ripped in a northeasterly direction through southern Brooks, Cook, and Berrien counties, killing 11 people and devastating parts of several communities. Four other people died in tornadoes near the city of Albany in southwestern Dougherty County, and one person was killed in northern Florida’s Columbia County. Tornadoes also touched down as the storm front crossed South Carolina.

The powerful southern storm prompted the U.S. National Oceanic and Atmospheric Administration (NOAA) Storm Prediction Center to issue a rare “high risk” severe weather outlook early Sunday—the first such “high risk” day since June 2014 when storms raked through Nebraska, Iowa, and Missouri.

December 1, 2016

Emergency medical services personnel in Melbourne, Australia, dealt with an unprecedented number of calls last week from people suffering respiratory symptoms as a freak weather event known as “thunderstorm asthma” swept the city. Doctors are still treating dozens of patients for a variety of serious respiratory conditions, and at least eight people have died. Meanwhile, scientists are trying to understand how this rare and little-understood event occurred.

Clouds gather over Melbourne, Australia, where recent thunderstorms have caused fatal asthma attacks. Credit: © Sunflowerey/Shutterstock

Asthma is a lung condition characterized by breathlessness, wheezing, and coughing. People with asthma suffer from inflammation of the bronchi (airways to the lungs). The inflamed airways react to irritation by swelling and constricting. These changes obstruct airflow (the ability to force air in and out of the lungs). A person may feel short of breath or have difficulty breathing. Severe attacks may involve spasms (sudden constriction) of the airways. Sufferers gasp for air and feel that they are suffocating. These attacks require immediate medical attention and can cause death.

A variety of environmental conditions, called triggers, may irritate the sensitive airways of people and cause an asthma attack. Triggers include pollen, mold spores, chemical irritants, tobacco smoke, animal dandruff, and dust mites. The term thunderstorm asthma refers to rare weather events where large storms generate powerful winds that churn up pollen and dust into the air. Recent hot, dry weather around Melbourne led to large ryegrass pollen deposits in the region. Once this pollen was in the air, thunderstorm winds ruptured the pollen grains into even smaller particles. These particles were small enough to be inhaled deep into people’s lungs, causing irritation and acute asthma attacks.

The last recorded outbreak of thunderstorm asthma in Australia was in 2010. That event was not nearly as severe as the one that occurred last week. Scientists worry that such unusual weather events will become more frequent and more deadly in Australia because of climate change.

February 22, 2016

A visible image of Tropical Cyclone Winston taken from the VIIRS (Visible Infrared Imaging Radiometer Suite) satellite on February 19, 2016. Credit: NASA

On Saturday, February 20, Tropical Cyclone Winston made landfall on the South Pacific island nation of Fiji. (Such storms as tropical cyclones are known as hurricanes when they occur in the North Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico, or the Northeast Pacific Ocean.) Winston reached wind gusts as high as 224 miles (360 kilometers) per hour, with sustained winds of 185 miles (298 kilometers) per hour. It was a Category 5 storm (the strongest storm level), which is a storm with sustained winds of at least 156 miles (250 kilometers) per hour. Winston is the strongest tropical cyclone on record for the Southern Hemisphere. 

Thousands of people in Fiji have been evacuated from flooded and devastated areas. The death count stands at 21 people, but this is expected to rise as authorities reach outlying islands. Fiji is an archipelago made up of 300 islands, some of which are fairly remote.

Many areas of Fiji have lost electric power and are flooded. Aid workers fear both disease and hunger for Fiji’s population of 900,000. Many crops were destroyed in the storm.

Other World Book articles

• How the Ocean Affects Climate (a Special report)
• Weathering the Storm: Adapting to Global Warming

In the eastern United States, winter storms brought record snows over the weekend of January 23. Credit: AP Photo

January 22, 2016

A winter storm that has been predicted for the last week has finally hit the southeastern United States. On Friday afternoon, January 22, the storm covered the southeastern United States—including North Carolina and Virginia—with 7 to 9 inches (17.5 to 23 centimeters) of snow. According to the National Aeronautics and Space Administration (NASA), the storm’s size was huge. It will move up the East Coast, dropping snow for the entire weekend. Some regions in the storm’s path are expected to receive as much as 30 inches (76 centimeters) of snow. Some areas will also see high winds, blizzard conditions, and storm surges (sudden onrushes of tidal waves caused by strong winds) with flooding.

As the storm travels up the Coast into such areas as Massachusetts, New Jersey, and New York, it will be striking in areas used to heavy snowfall. The southern United States region, however, is far less used to snowfall. Two feet (61 centimeters) or more of snow are predicted for the Washington, D.C. region. That region receives an average of 14.5 inches (37 centimeters) per year.

Some 50 to 75 million people will be affected by the storm. Subways in Washington, D.C., were closing for January 22 through January 24. Almost 3,000 flights were canceled on January 22, mostly in the south. Another 3,000 flights were canceled for January 23.