By the Light of the Slivery Moon
The captivating crescent may be the Moon’s most fascinating phase. Why is the crescent Moon sometimes on its back, bottom, side, or upside down? Is it smiling at you? Bob explains the crescent Moon tilt.
Look for that sly, slim smile. When first sighted each month, hovering in twilight, the Moon’s slender crescent is mesmerizing. Early cave paintings reveal a primitive fascination with the crescent Moon, and its allure continues to this day.
(See tonight’s Moon phase in your area with the Almanac’s Moon Phase Calendar.)
Ever noticed: The crescent Moon is always low in the sky and confined to the hours around dawn or dusk; it is never in darkness.
Cartoonists often depict the crescent Moon in a midnight sky, but this is impossible: The night’s middle hours are for the broad, or fat, phases of the Moon—gibbous and full.
What is a Crescent Moon?
When the Moon appears early in its first quarter or late in its last quarter, only a small arc-shaped section is visible and illuminated by the Sun.
The orientation of the crescent Moon depends on the time of day, the season, and the viewer’s location.
- During evening twilight, from January through March, in all of the northern temperate latitudes (from 25° to 50° north latitude, encompassing Canada, China, all of Europe, Japan, Russia, and the United States), the changing angle of the lunar orbit with respect to the horizon orients the crescent with its points, or horns, aimed upward, displaying a benevolent smile.
- For the remainder of the year, the crescent appears sideways, like an archer’s bow.
At no time of night from any location on Earth does the Moon appear to be frowning; this occurs only around midday, in full sunlight.
The year-round view from the tropics is of a smiling crescent.
Credit: Dominic Gentilcore/Shutterstock
In northern polar regions (Alaska, the Yukon, the Northwest Territories, and Nunavut), the crescent always points sideways.
North, South; Left, Right—The Same, but Different
In both the Northern and Southern Hemispheres, the shape and width of the crescent Moon is the same on the same day. However, the angle of the crescent’s orientation differs. The crescent’s illumination is always aimed at the Sun, while its points, or horns, aim directly away from the Sun.
In the Northern Hemisphere, the Moon stands above or (more usually) to the upper left of the sunset point.
In the Southern Hemisphere, it stands to the upper right of the sunset point. The crescent’s “tilt” looks different from each place.
What does the crescent moon symbolize?
Numerous cultures this centuries-old tradition: They call the first sighting of the crescent Moon after its monthly 3-day absence the “new Moon.” (The 3 days include the 36 hours before the new Moon and the 36 hours after it.)
For example, among followers of Islam, the first sighting marks the start of each month and determines fast times and holidays.
Today, to astronomers and scientists, “new Moon” means “no Moon.” The phrase describes the date and hour when the Moon is closest to the Sun and completely obscured from Earth by solar glare. Two days and 26 degrees later (the Moon appears to move leftward 13 degrees every 24 hours), when the Moon is not in line with the Sun and therefore is only marginally in view, the waxing crescent appears just above the western horizon, setting soon after sunset.
When the crescent Moon appears in early twilight, a strange but famous feature becomes visible: The dark portion of the Moon (the area unlit by the Sun) seems to glow. Historically called “the new Moon in the old Moon’s arms,” the phenomenon is now aptly known as earthshine. Learn more about Earthshine!
After sunset, the crescent Moon’s points, or horns, always aim directly away from the sunset. Imagine the crescent as an archer’s bow: The invisible arrow is aimed directly at the Sun, which is below the horizon. Each succeeding night at the same time, the waxing crescent sits higher in the sky and farther left, in an increasingly sideways orientation. The Moon stays out longer before setting and becomes an increasingly nighttime (not twilight) phenomenon.
Simultaneously, the Earth-lit portion shrinks and dims; Earth is shrinking into a thinner phase in the lunar sky. Just 4 or 5 days after the Moon’s “new” phase, it opens up more than a 45-degree angle from the Sun and is high in the southwest when twilight ends.
At the age of 23 days (the time since the last “new” phase), the Moon enters a second crescent cycle. This waning, predawn sliver receives less attention than its waxing evening cousin. Rising
only after midnight, it appears monthly for 5 consecutive days. Seen only in the eastern sky, with its points, or horns, aiming rightward (the opposite of the evening form), it heralds the dawn.
Its size foretells the time:
- A broad waning crescent normally appears between 1:00 and 2:00 a.m. but occasionally around midnight.
- A slim crescent rises in full darkness, just before morning twilight.
- A thin sliver of crescent appears only in morning twilight and always low in the sky
The Crescents of Planets
Even through the world’s most powerful telescopes, only two other crescents can be seen from Earth—those of planets Mercury (near right) and Venus (far right). The dearth of crescents is because of
Earth’s location: We can see the crescents only of planets between us and the Sun.
If we lived on Pluto, all of the planets in our solar system, as well as the numerous moons of Jupiter, Saturn, and Uranus, would be lit from behind and appear as crescents half of the time.
Image: Planet Mercury. Credit: NASA / JHUAPL / CIW
Viewing the Crescent Moon
Finding the hair-thin lunar arc each month has become a fun sport. Today, millions of people—amateur astronomers, nature enthusiasts, and casual observers—even compete to find the
“youngest” Moon. (The lunar age is the number of hours or days that have elapsed since the Moon became new. See your Moon Phase Calendar. )
The best crescent-spotting conditions in the Northern Hemisphere occur from January through March, as the Moon’s path (its day-to-day change of position) moves nearly vertically
up from the sunset point. During the rest of the year, the line follows a horizon-scraping, leftward slant.
- Since 1990, the youngest Moon sighted with the naked eye has been 15-1⁄2 hours old. Thirteen-hour-old crescents have been viewed with binoculars.
- A wee 1-day-old Moon (the orb exactly 24 hours after it was officially “new”) looks as thin as a wire, is very close to the skyline, and is usually mired in thick horizon haze. It is almost impossible to see in autumn.
- A 2-day-old Moon is easy to spot: It is relatively broad, or fat; higher above the horizon (8 degrees, on average) than it was the previous day; and viewable 15 minutes or so after sunset.
Would you like to see a slivery Moon? Find its phase time for your location at our Moon Phase Calendar.