Plants grown in simulated lunar soil on the left and in Apollo sample on the right, seen 16 days after planting.
Credit: Tyler Jones, UF/IFAS

Well, not exactly. Scientists recently grew plants in lunar soil for the first time in history. The lunar soil, also called moon dust, was brought back from three Apollo missions. Scientists from the University of Florida planted thale cress in the moon dust and compared the growth to materials found on Earth’s surface, such as volcanic ash. Thale cress is a small, bitter-tasting plant similar to broccoli, cauliflower, and kale. After two days, the seeds had germinated (grown). However, the plants in moon soil did not thrive compared to the plants in Earth soil after six days.

Lunar soil is very different from the soil on Earth. Soil is the mixture of minerals, organic matter, and other materials that covers most of Earth’s land. Soil is a storehouse of nutrients and the decayed remains of organisms (living things). Lunar soil is more dusty and is not made up of decayed organisms, so it does not contain as many nutrients compared to soil found on Earth. Impacts of micrometeoroids (tiny meteoroids‘) grind the surface rocks into a fine, dusty powder known as regolith. Regolith overlies all the bedrock on the moon. Because regolith forms as a result of exposure to space, the longer a rock is exposed, the thicker the regolith that forms on it.

National Aeronautics and Space Association (NASA) granted the scientists 12 grams of lunar soil for the experiment because it is precious and cannot be wasted. The soil brought back from Apollo 11 was not as strong as the soil brought back from Apollo 12 and 17. The scientists believe soil from Apollo 11 was damaged by cosmic rays and radiation from solar wind on the moon’s surface. Scientists have already started planning where they could find better moon soil where lava flow has enriched the soil.

For years, scientists have wondered whether the moon could support life. If humans were to survive on the moon permanently, they would need to grow plants for food. Although the experiment did not prove that the moon could sustain life, it gives hope that there could be vegetation on the moon someday. We are one step closer to growing an herb garden on the moon!

Jessica Watkins
Credit: NASA

American astronaut and geologist Jessica Watkins is making history this month. She is the first Black woman selected for an extended mission in space. Watkins and three other astronauts launched aboard a new SpaceX Crew Dragon spacecraft named Freedom atop a Falcon 9 rocket on April 27, 2022. Once the crew arrives, they will work and live aboard the International Space Station (ISS). The ISS is a large, inhabited Earth satellite that more than 15 nations are operating in space. Watkins is set to work aboard the station for six months. On the ISS, she will work at the microgravity laboratory and serve as the team’s mission specialist.

Jessica Andrea Watkins was born in Gaithersburg, Maryland, on May 14, 1988. Her family later moved to Lafayette, Colorado. She enrolled at Stanford University in California, in 2006.  Watkins led Stanford’s rugby team to win the 2008 national championship. Watkins was a member of the United States Women’s Eagles Sevens Rugby team, competing in the 2009 Women’s Sevens Rugby World Cup in Dubai. Watkins earned her bachelor’s degree in geological and environmental sciences from Stanford University in 2010.

Watkins studied and worked extremely hard to reach her new career in space. Watkins earned a doctorate degree in geology at the University of California, Los Angeles, in 2015. Watkins conducted post-doctoral research at the California Institute of Technology (Caltech). At UCLA, she studied landslides on Mars. At Caltech, she helped plan missions for the National Aeronautics and Space Administration (NASA) Curiosity rover.

As an undergraduate, Watkins participated in an internship for NASA at the Ames Research Center outside of San Jose, California. She compared simulated Martian soils with data gathered by the Phoenix Mars Lander.  In 2009, Watkins served as the chief geologist for a simulated mission at the Mars Desert Research Station outside of Hanksville, Utah. As a graduate student, she interned for the Jet Propulsion Laboratory in Pasadena, California. In 2017, Watkins was selected for astronaut training. In 2019, Watkins participated as an aquanaut in a simulated space mission at the NASA Extreme Environment Mission Operations (NEEMO) Aquarius habitat, on the ocean floor off the coast of Key Largo, Florida. NASA has also selected Watkins as a crew member for the Artemis mission to the moon’s surface.

April 1, 2020

Today is the first day of April, the fourth month of the year according to the Gregorian calendar, which is used in most of the world today. In the Northern Hemisphere, April is the first full month of spring. (In the Southern Hemisphere, April occurs in autumn.) Many flowers bloom in April, including the pink phlox, a type of garden plant with brilliantly colored blossoms. The profusion of blooming pink phlox gives April’s full moon its name. The “Pink Moon“—the second of three consecutive supermoons—rises on April 7. A supermoon occurs when the moon is at perigee, the point when it is nearest the Earth and thus appears slightly brighter and larger in the sky.

The full moon of April is known as the “pink moon” because of the widespread blooming of pink phlox during the month. Credit: WORLD BOOK illustration

The name April comes from the ancient Roman word for the month, Aprilis. This name might have come from a word meaning to open, or from the name of Aphrodite, the Greek goddess of love (called Venus in Roman mythology). April was the second month in the early Roman calendar. However, it became the fourth month when the beginning of the year was moved from March to January. On the first of April, April Fools’ Day, people all over the world cause mischief and play tricks on each other.

Many cultures celebrate the arrival of spring, or other aspects of the natural world, in April. Walpurgis Night is a spring celebration held in Germany, Finland, and Sweden on April 30. People there welcome spring with bonfires, singing, and parties. The Japanese Cherry Blossom Festival Sakura Matsuri takes place in April. In the Netherlands, flower parades are held toward the end of April, when the tulips are blooming. Many people plant trees on Arbor Day, which occurs on different dates in different countries. Many nations celebrate Earth Day on April 22. This holiday was organized in 1970 to raise awareness of the environment. The Angolan Feast of Nganja, a celebration of the corn harvest, always occurs in April.

Some cultures welcome the New Year in this month. Nava Varsha, the Nepalese New Year, falls on or near April 13. Several countries in Southeast Asia, including Cambodia, Laos, Myanmar, and Thailand, also celebrate the New Year at this time. In Thailand, the holiday is called Songkran.

Chakri Day, April 6, marks the date in 1782 when King Rama I took control of the government of Siam (now Thailand). Matatirtha Aunsi, Nepalese Mothers’ Day, also falls in April. The Christian celebration of Easter often occurs in this month, as does the Jewish festival of Pesah, also known as Passover.

September 13, 2019

Last week, on September 6, an up-and-coming space agency fell just short of its goal. About 1 mile (1.5 kilometers) above the moon’s surface, the India Space Research Organization (ISRO) lander Vikram deviated from its landing course and disappeared from radio contact. Vikram was to be the crowning stage of Chandrayaan-2 (Mooncraft-2), ISRO’s second lunar mission.

This artist’s depiction shows Chandrayaan-2′s lunar lander, Vikram, approaching the moon. Credit: © Raymond Cassel, Shutterstock

India was endeavoring to become the fourth country to make a soft landing (a landing that does not destroy the craft) on the surface of the moon, after the United States, the former Soviet Union, and China. Vikram would have been the first lander near the moon’s south pole, a region full of water ice and other minerals that could one day be the site of a permanent base. Vikram would have deployed a rover to explore the landing site. The Chandrayaan-2 orbiter, which had launched Vikram, located the lander on the surface of the moon a few days after its disappearance. ISRO reported that Vikram had apparently made a “hard landing,” and the lander did not respond to contact attempts.

Before the recent failure, ISRO had been riding a wave of success. In 2008, the agency deployed its first lunar satellite, Chandrayaan-1. Chandrayaan-1 mapped the moon’s surface for about a year. The satellite also released a hard lander that impacted the lunar surface. In 2013, ISRO launched the Mars Orbiter Mission, called Mangalyaan (Marscraft). The satellite overcame a minor engine failure to reach Martian orbit in September 2014.

ISRO’s failed soft landing on the moon comes on the heels of another prominent lunar failure. In April 2019, the lander Beresheet (In the Beginning), developed by the Israeli company SpaceIL, slammed into the moon when its main engine cut out unexpectedly. SpaceIL had hoped to become the first private company to place a lander on the moon’s surface. It had been one of the competitors for the Google Lunar X Prize. The contest would have awarded $20 million to the first company to achieve a soft landing on the moon. But none of the competitors attempted a landing, even after several deadline extensions, so the prize was withdrawn. The Israeli project cost about $100 million, a fraction of what a similar mission by the United States National Aeronautics and Space Administration (NASA) would have cost, but it took greater risks and ultimately failed.

The process of landing is the most dangerous phase of a lander’s mission. Many different systems must work perfectly for the lander to bring itself to a halt on the surface. Any malfunction is usually catastrophic. At other points in a mission, such as in transit to or in orbit around another body, engineers have plenty of time to identify and work around problems with a spacecraft. But this cannot be done in the time-sensitive environment of landing.

July 19, 2019

On July 20, 1969, 50 years ago tomorrow, the United States astronauts Neil Armstrong and Buzz Aldrin did what had seemed impossible not that long before: they landed on the moon. Watched by millions of people over a live television broadcast worldwide, Armstrong and Aldrin’s lunar first was the crowning moment of the National Aeronautics and Space Administration’s (NASA) Apollo space program.

Astronaut Buzz Aldrin took this photo of Neil Armstrong working on a storage assembly on the lunar module, Eagle, on the surface of the moon in July 1969. Credit: NASA

In May 1961, President John F. Kennedy proposed landing astronauts on the moon by the end of the decade. This goal seemed out of the realm of possibility at the time. The United States was trailing the Soviet Union in the space race, a period of intense competition between the two countries to achieve supremacy in space exploration. The Soviet Union had already launched the first satellite (Sputnik in October 1957) and the first person (cosmonaut Yuri Gagarin in April 1961) into orbit around Earth. American efforts had been riddled with launch failures, and the greatest success at that time had been a brief suborbital flight (astronaut Alan Shepard spent a few minutes in space) shortly before Kennedy’s announcement. From the looks of things in 1961, if anyone was going to land on the moon before 1970, it would be a cosmonaut.

A NASA Saturn 5 rocket launches from Florida’s Kennedy Space Center on July 16, 1969, carrying the Apollo 11 astronauts who would land on the moon days later. Credit: NASA

NASA, however, accepted the challenge with intensity and enthusiasm. It wound down the initial Mercury space project and began the Gemini program. Gemini helped develop the technology and skills to travel to the moon. Astronauts were launched in pairs, and they practiced docking with other spacecraft—an important part of Apollo’s novel mission design. The astronauts also practiced more precise ocean landings, to gain skill for lunar touchdowns. Gemini ended in 1966 and was succeeded by Apollo.

The Apollo program started with disaster. In January 1967, a fire during a pre-launch test took the lives of astronauts Roger B. Chaffee, Virgil I. (Gus) Grissom, and Edward H. White II. After the accident, NASA engineers redoubled their focus on crew safety.

Apollo 11 astronaut Buzz Aldrin stands on the surface of the moon in July 1969. Credit: NASA

After several crewed and uncrewed Apollo test flights, NASA was ready to land the first people on the moon. On July 16, 1969, a Saturn 5 rocket, the most powerful rocket ever built, launched from Kennedy Space Center carrying the three astronauts of Apollo 11. After three days in transit, the mission entered into orbit around the moon. On July 20, Armstrong and Aldrin landed on the surface in the lunar lander module, named Eagle. Fellow astronaut Michael Collins stayed aboard a command module orbiting the moon.

This photo taken during the Apollo 11 mission shows Earth rising above the surface of the moon. Credit: NASA

As the mission commander, Armstrong was the first person to leave the lunar module and set foot on the surface. Upon taking his first step onto the moon, he famously said: “That’s one small step for [a] man, one giant leap for mankind.” (The word “a” was lost in radio transmission.) Aldrin joined him on the surface about 20 minutes later. They explored the lunar surface for more than two hours, performing experiments, setting up scientific equipment, and collecting samples of the lunar surface. Then, they blasted off in the lunar module, reunited with Collins in orbit around the moon, and safely returned to Earth.

Armstrong, Aldrin, and Collins were greeted with honors and awards upon returning home, including the Presidential Medal of Freedom, one of the two highest civilian honors awarded by the U.S. government. (They were awarded the second highest honor, the Congressional Gold Medal, in 2011.) The lunar astronauts received huge parades in New York City, Chicago, and Los Angeles. They were celebrated in their home towns as well as at state dinners around the world.

Astronaut Buzz Aldrin stands next to a seismograph on the lunar surface in July 1969. The lunar module, Eagle, stands in the background. Credit: NASA

Armstrong never became fully comfortable with the fame associated with being the first person to walk on the moon, refusing most interview requests until his death in 2012. Aldrin, however, enjoyed the spotlight and continues to be a prominent spokesperson for the advancement of human space exploration. Collins would have likely been selected to finally walk on the moon as the commander of Apollo 17—the last moon mission. But he retired from NASA after Apollo 11, happy to have been a vital—albeit relatively invisible—part of the first moon mission.

After six successful moon landings, Apollo was cancelled and NASA turned its attention to the development of the space shuttle. Humans have not left Earth’s orbit since since Apollo 17 in December 1972. That could change soon, however, as the United States and many countries and private companies are seeking to return to the moon in the near future. The American spacecraft company SpaceX is developing a rocket and lander intended to orbit and land on the moon. Another company, Blue Origin, is also developing rockets and landers with the ultimate goal of building a permanent settlement on the moon.

December 26, 2018

On Dec. 26, 1968, 50 years ago today, United States astronauts of the Apollo 8 mission prepared to reenter Earth’s atmosphere after becoming the first humans to orbit the moon. Apollo 8 was part of the Apollo space program that eventually landed people on the moon. The program lasted from 1961 to 1975. It was conducted by the National Aeronautics and Space Administration (NASA). Live telecasts by the Apollo 8 astronauts were shown around the world, including a famous Christmas Eve broadcast that, at that time, was the most watched television program in history.

The Apollo 8 crew–astronauts Frank Borman, James A. Lovell Jr., and William A. Anders–prepare to board a van which will transfer them to the launch pad at Florida’s Kennedy Space Center on Dec. 21, 1968. The crew orbited the moon and returned safely to Earth on December 27. Credit: JSC/NASA

Apollo 8 launched on Dec. 21, 1968, with astronauts William Anders, Frank Borman, and James Lovell, Jr. It was the second piloted Apollo mission, following Apollo 7 that had tested equipment in low orbit two months earlier. After separating from the carrying Saturn V rocket, the Apollo 8 astronauts guided the command and service module, or CSM, through trans-lunar injection, a maneuver sending the spacecraft toward the moon. The CSM entered lunar orbit and then passed to the dark side of the moon. People on Earth held their breath as communications were lost—as expected—for several minutes. Contact then resumed and was lost and resumed again as the CSM orbited the moon 10 times over 20 hours.

Apollo 8 astronaut William Anders took this famous photograph–known as Earthrise–on Christmas Eve, Dec. 24, 1968. The lunar surface can be seen in the foreground. Credit: NASA

The NASA telecasts took place just before, during, and after these orbits, and the astronauts took a series of remarkable photographs—including the famous “Earthrise” and other photos that showed humans what our planet looks like from space. On December 27, Apollo 8 returned to Earth, splashing down in the Pacific Ocean near the recovery ship Yorktown, 147 hours after launch and precisely on time.

This official emblem of the Apollo 8 lunar orbit mission featured the names of the crew: Frank Borman, commander; James A. Lovell, Jr., command module pilot; and William A. Anders, lunar module pilot. Credit: NASA

Apollo 9 and 10 carried out further tests before Apollo 11 landed humans on the moon for the first time in July 1969. Five more Apollo missions landed astronauts safely on the moon through December 1972.

August 22, 2017

Yesterday, on August 21, huge crowds gathered across the United States to watch the solar eclipse within the path of totality, the 70-mile (113-kilometer) wide swath of land from Oregon to South Carolina where the moon completely covered the sun. In Newport, Oregon, throngs of sky watchers greeted the eclipse as it made first landfall at 10:15 a.m. local time. Many thousands of eclipse chasers filled the totality town of Carbondale, Illinois (where the eclipse was longest). Local merchants greeted the tourists with special jewelry, cookies, doughnuts, and other eclipse-themed goods. Across the country, roads toward the path of totality were jammed with traffic and hotels were booked solid—sometimes a year or more in advance of the big event.

This photograph, taken from Northern Cascades National Park in Washington, shows the moon passing before the sun during the solar eclipse of Aug. 21, 2017. Credit: Bill Ingalls, NASA

A total solar eclipse can have a powerful psychological effect on people. Many people, especially in large urban areas, don’t often have reason to look toward the sky in the middle of the day. But, as the moon begins to move over the sun, people could not help but notice the odd darkening of the sky unlike anything they had ever seen. Many people reported feeling a profound sense of awe and a spiritual connection with other people. Others reported a tremendous feeling of unease as the sunlight dimmed and gradually faded completely. But, unlike the experience in ancient times, there were no reports of panic among the masses of eclipse watchers. Astronomers have long been able to precisely predict the time and place of such celestial events. Yesterday, people cheered and applauded the eclipse as they might ooh and aah at a fireworks show, and eclipse glasses (with lenses dark enough to safely view the sun) were passed from hand to hand.

The moon totally blocks the sun during the solar eclipse of Aug. 21, 2017, above Madras, Oregon. Only the sun’s corona is visible around the moon. Credit: Aubrey Gemignani, NASA

At peak totality, the bright disk of the sun was replaced by a dark spot, surrounded by a blazing ring–the sun’s outer atmosphere (called the corona) that is easily visible only during an eclipse. In some regions, people felt a noticeable temperature drop as day briefly turned to night. Stars and planets became visible in the midday sky. Crickets began chirping, thinking night had begun a bit early, and birds roosted and went silent. Some eclipse chasers were surprised and annoyed by mosquitoes, which were fooled into thinking dusk had arrived and went hunting a few hours early.

People gaze skyward wearing eclipse glasses during the solar eclipse of Aug. 21, 2017, on the Oregon State University campus in Corvallis, Oregon. Credit: Mark Floyd, Oregon State University (licensed under CC BY-SA 2.0)

The great solar eclipse of 2017 left the United States just north of Charlotte, South Carolina, at 4:10 p.m. local time. Peak totality ended at 2:49 p.m. at that location. Anyone who missed the eclipse this year will not have to wait long for another chance. The next total solar eclipse visible from a large portion of the United States will occur on April 8, 2024. And Carbondale, Illinois, will once more have a chance to shine. It is the only city that will be in the path of totality in both 2017 and 2024. It’s not too early to start planning!

August 18, 2017

Get ready! On Monday, August 21, if you live in the United States from Oregon to South Carolina, you will be able to experience one of nature’s most impressive sights–a total eclipse of the sun. Across the United States, large crowds are expected in towns, cities, and campsites along the path of totality for the spectacular celestial show. The path of totality is the narrow swath, about 70 miles (110 kilometers) wide, along which the moon will completely blot out the sun.

A solar eclipse occurs when the moon passes between Earth and the sun, blotting out the sun’s light. This photograph shows a total eclipse, in which the moon completely covers the face of the sun. The sun’s outer atmosphere, called the corona, appears as an irregularly shaped halo of light. Credit:

A total solar eclipse occurs when the Earth, sun, and moon are in nearly a straight line and the moon’s shadow sweeps across the face of Earth. The dark moon appears on the edge of the sun and moves slowly across. At the moment of totality, a brilliant halo flashes into view around the darkened sun. This halo is the sun’s outer atmosphere, the corona. The sky remains blue but darkens dramatically. Some bright stars and planets will become visible and the temperature will noticeably drop. After a few minutes, the sun reappears as the moon continues on its orbit. The period when the sun is totally darkened may be as long as 7 minutes 40 seconds, but it averages about 2 1/2 minutes.

A total eclipse of the sun, as shown here, starts at the left. The moon gradually covers the sun, shown photographed through a filter. At the time of the total eclipse, photographed without a filter, the sun’s corona (outer atmosphere) flashes into view. The sun reappears as the moon moves on. Credit: © Atlas Photo Bank/ Photo Researchers

In the United States, the path of totality will cross 14 states: Oregon, Idaho, Wyoming, Montana, Nebraska, Iowa, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina, and South Carolina. This will be the first total solar eclipse to cross the United States from coast-to-coast since June 8, 1918, when a total solar eclipse darkened skies from Washington to Florida. The last total solar eclipse to be seen anywhere in the continental United States was in 1979.

Makanda, a village in southern Illinois just south of Carbondale, will see the longest duration of totality for the eclipse–about 2 minutes and 40 seconds. If you miss out, though, don’t worry. Another total solar eclipse will cross the same area in 2024!

If you are going to view the eclipse, be careful! Looking directly at the sun, even during an eclipse, can severely damage your eyes, even if you are wearing sunglasses. If you wish to look directly at the eclipse you will need “eclipse glasses” which have special solar filters. Make sure that your eclipse glasses are undamaged and meet safety standards. Be careful to look away from the sun when you put your eclipse glasses on and take them off. A total solar eclipse can be viewed safely without protection in the path of totality only during the brief time when the disk of the sun is completely hidden.

More on this story next week!

February 3, 2017

One of the greatest questions in the formation of the solar system is in our own planetary back yard: how was the moon made? The current hypothesis (proposed explanation)—that the moon formed from chunks of Earth unloosed in a massive collision—has held sway among planetary scientists for over 30 years. But as more is learned about the moon, scientists are exploring other possibilities, and three scientists in particular—Raluca Rufu and Oded Aharonson of the Weizmann Institute of Science, Israel, and Hagai B. Perets of the Technion Israel Institute of Technology—are offering a different explanation. They published their new theory last month in the journal Nature Geoscience.

A new theory suggests that the moon may have formed from debris unloosed by many small impacts on Earth rather than one big one. Credit: Lunar and Planetary Institute

Since the early days of astronomy, people have speculated on how the moon was formed. In the 1800’s, astronomers used to think that the moon split from Earth—but in a very peculiar way. The accepted hypothesis of that era said that in the distant past Earth spun so rapidly that a portion of it tore away, forming the moon and leaving behind a basin that became the Pacific Ocean. Scientists now know that plate tectonics formed the Pacific Ocean over hundreds of millions of years, and that Earth lacks the rotational speed to create such a spectacular split. In recent years, engineers have developed powerful computers that allow geologists to take new and closer looks at rocks returned from the Apollo moon landings from 1969 to 1972.

This artist rendering depicts the “Big Whack” hypothesis of Earth colliding with a planetary body. The resulting dust and debris from Earth would then have created the moon. (Credit: NASA/JPL-Caltech)

Since the 1980’s, one hypothesis has stood up best to scrutiny: that the moon formed as a result of a massive collision known as the Giant Impact or the “Big Whack.” According to this idea, a Mars-sized object collided with Earth about 4.6 billion years ago. As a result of the impact, a huge cloud of vaporized rock shot off Earth’s surface and went into orbit around Earth. The cloud cooled and condensed into a ring of small, solid bodies, which then gathered together, forming the moon.

If the Big Whack is favored, why are Rufu, Aharonson, and Perets exploring alternative ideas? The Big Whack explains many of the orbital and rotational characteristics of both Earth and the moon, but the hypothesis must be tweaked to an uncomfortable degree to account for the remarkable similarity of Earth rocks to moon rocks. The giant impactor would have had to have struck Earth in an extremely precise way to produce a moon with the makeup shown by returned lunar samples.

Therefore, the Israeli team started from scratch. They reasoned that because impacts were common in the early solar system, Earth should have been hit with objects large enough to create moons many times, not just once. They ran hundreds of computer simulations and found that a series of smaller impacts over the course of millions of years could explain the compositional similarity of Earth and its moon. A smaller body (more the size of the dwarf planet Ceres) would slam into Earth, forming a disk of debris that would eventually come together to form a moonlet, or mini-moon. Later, another body would collide with Earth, creating a new debris disk and another moonlet. Eventually, these moonlets would merge with one another. To reach the size of the current moon, a number of such collisions and moonlet creations and mergings (their guess was roughly 20) would be needed.

The new study is intriguing, but it does not disqualify the Giant Impact Hypothesis just yet. Rufu and her colleagues admit that much more research needs to be done to confirm their findings. For instance, the group did not determine if some of the moonlets could have been sucked back into Earth or flung out into the solar system. This would increase the number of impacts needed to make our moon, making this explanation less likely than a precise Giant Impact.

July 31, 2015

A full moon rises over Earth in a photo take from the International Space Station. Tonight, the second full moon of the month—the blue moon—will appear in the sky. (c NASA)

Is it the second full moon in a month? The third full moon in a season that has four full moons? An uncommon occurrence? A crazy idea? Over the years, the term “blue moon” has held many definitions. The definition that includes tonight’s full moon is a relatively recent—and accidental—invention.

As early as 1528, “blue moon” was a phrase used to mean a silly belief. In later times, people described uncommon events as occurring “once in a blue moon.” Additional definitions of the term refer to rare types of full moons. According to one definition, a blue moon is the second full moon in a month that has two full moons. According to an older definition, a blue moon is the third full moon in a season that has four full moons. The older definition was developed using a calendar in which spring always begins on March 21. In this calendar, the beginnings of summer, autumn, and winter are based on the position of an imaginary sun called the dynamical mean sun. Today, astronomers use a different rule for determining the beginnings of the seasons.

In the early 1900′s, the Maine Farmers’ Almanac published dates on which blue moons would appear, using the older definition. The newer definition of the second full moon in a month originated in Sky & Telescope magazine in 1946. Other publications adopted the definition, and many people came to accept it. In 1999, however, Sky & Telescope published an article explaining that the 1946 definition actually originated from a misreading of the Maine Farmers’ Almanac.

For all this talk about “blue” moons, can the moon ever actually turn the color blue? If certain tiny particles are in the atmosphere, the moon can, in fact, appear blue. Volcanoes and forest fires are the most common sources of these particles. For example, when the Indonesian volcano Krakatau erupted in 1883, people around the world reported seeing a blue-hued moon for years afterward. Such events are rare, however, so true blue moons could be said to only occur once in a blue moon! Confused yet?

Other links:

• Dates of blue moons (World Book table)
• Summer Blue Moon (NASA)