Ever gaze upon a full moon so big and bright it left shadows?
Such a moon gave our ancestors “a lot of light to see and do things,” says Dr. Mark SubbaRao, an astronomer at the Adler Planetarium in Chicago. The night sky once was incredibly dark and “those full moons became very important to people,” he says.
The moon doesn’t have its own light source; it gets its glow from the sun. And it always shows us the same illuminated face, Mark says. But as the moon orbits the earth, we may see only parts of this face at given times. These parts, or phases, have names: new moon, crescent moon, quarter moon, gibbous moon and full moon.
The first phase is the new moon, which we can’t see (unless it perfectly aligns with the sun in a solar eclipse.) Next comes the crescent moon: a sliver of illumination that grows as it moves on to quarter, gibbous and full moon. This part of the cycle, when the moon appears to grow bigger, is called waxing.
The full moon then becomes less visible as it wanes, or moves through the phases of gibbous, quarter and crescent on its way to new moon. The entire eight-phase cycle repeats every 29 days or so.
The cycle’s predictability helped early people track time. They created lunar calendars, which we still use today to determine dates of traditional holidays and even when to plant crops.
Planting by the Moon
For centuries, farmers and gardeners have relied on the moon to guide the sowing of seeds. Many believe the moon’s gravitational pull, stronger during full and new moons, causes groundwater and plant sap to rise just like the tides rise in the oceans, says Lyn Bagnall, author of “Easy Organic Gardening and Moon Planting” for Australian gardeners.
When the moon is waxing, water tables are higher, and the increased moisture helps the seeds of above-ground crops like lettuce, broccoli and annual flowers, germinate faster, says Mare-Anne Jarvela, senior editor of “The Old Farmer’s Almanac.” The extra night-time light also helps seedlings get off to a better start, she says.
Planting when the moon is waning is best for root crops like potatoes, beets and carrots, Mare-Anne says. The water table is lower and less moonlight is available, allowing seeds to develop good root systems, she explains. This often is called planting “in the dark of the moon,” but it doesn’t mean you have to work in your garden at night, she says.
The Old Farmer’s Almanac lists the best dates for moon planting by region.
The Pull of the Moon
Though scientists dismiss moon planting as folklore, they do agree the lunar cycle affects insects and animals.
Gene McAvoy, a horticulture extension agent at University of Florida, says nocturnal moths use the moon as a “navigating tool,” flying more widely and frequently under a full moon. A few days later, farmers experience “spectacular” numbers of plant-eating caterpillars, like army and earworms, he says.
The “breeding cycles of many life forms on our planet are related to the moon phases,” Lyn says. These include species from biting midges to marine animals. One study suggests the menstrual cycles of some women coincide with the moon cycle, though this is not widely accepted.
Early psychologists believed the full moon caused madness, coining the term “lunatic” from the Latin “luna,” or moon. Folklore claims it turns some into werewolves. People today still believe the full moon causes strange behavior, resulting in more traffic accidents, crimes and suicides, but data doesn’t support this.
A Moon by Any Other Name
Native Americans in the northern and eastern United States named full moons after the seasons or tasks like growing, hunting and fishing, Mare-Ann says.
January: Wolf Moon
February: Snow Moon
March: Worm Moon
April: Pink Moon
May: Flower Moon
June: Strawberry Moon
July: Buck Moon
August: Sturgeon Moon
September: Harvest Moon
October: Hunter’s Moon
November: Beaver Moon
December: Cold Moon
Our Fascination Continues
For four years, NASA’s high-tech Lunar Reconnaissance Orbiter has circled the moon, revealing a far more complex and dynamic world than scientists realized.
Instruments have measured the amount of hydrogen trapped in lunar soil, suggesting ice can be found in the deep craters of the moon’s South Pole. And a high-res camera has helped scientists create a precise 3-D map of the moon’s surface. The images are so detailed “you can see the trails from astronauts walking on the moon,” says Mark, who uses some of these images in Adler Planetarium displays and sky shows.
These discoveries are helping us figure out where to land when we go back to the moon, Mark says.
Wax On, Wax Off
Here’s an easy way to tell if the moon is waxing (growing more visible) or waning (growing less visible):
Hold your hands in front of you with thumbs extended. Now channel the movie, “The Karate Kid.” Your right hand is wax on; your left hand is wax off.
If the visible part of the moon can be covered with your right hand, the moon is waxing. Soon it will be a full moon. If your left hand covers the moon, the moon is waxing off, or correctly put, waning. Soon the moon will be a new moon. Waxing and waning each take about 14 days.
Here’s the caveat: The trick only works in the Northern Hemisphere. If you live in the Southern Hemisphere, reverse the names of your hands: Your left hand becomes wax on; your right becomes wax off.
Scientists believe high tides caused by a full moon increased the devastating storm surge of Hurricane Sandy.
The word gibbous also means humpbacked. You can see the bulging shape of a gibbous moon before or after a full moon.
Because a lunar month is shorter than a calendar month, we sometimes have two full moons in a month. The second moon is called a blue moon.