On Dec. 20 the Moon appears as a very thin waxing crescent for most observers in the United States, while the New Moon instant occurs in some time zones. NASA notes the illuminated fraction reaches 0% at the New Moon instant, making the Moon effectively invisible around that moment. The next full moon falls on Jan. 3, and the Moon completes its 29.5-day lunar cycle as it moves through eight main phases.
Moon Phase Today: Thin Waxing Crescent in U.S.; New Moon Occurs in Some Time Zones on Dec. 20
An image of a full moon. - Photo by Omer Tarsuslu/Anadolu via Getty Images
Tonight the Moon appears as a very thin waxing crescent for most observers in the United States, while some time zones register the New Moon on the same night. Depending on the exact time and your location, the lunar illumination may be effectively zero at the instant of New Moon, making the Moon difficult or impossible to spot.
What to Expect Tonight
As of Saturday, Dec. 20, U.S. viewers will see a slim crescent just after sunset. NASA's Daily Moon Observations note that the illuminated fraction reaches 0% at the instant of New Moon in certain time zones, which means the lunar disk can be effectively invisible around that moment. If you want to try spotting the crescent, look low on the western horizon shortly after sunset when the sky is darkening but not yet fully night.
Upcoming Full Moons
The next full moon is expected on Jan. 3. The most recent full moon occurred on Dec. 4.
Why the Moon’s Appearance Changes
The Moon completes one orbit—and one lunar cycle—in about 29.5 days. During that time, the portion of the Moon lit by the Sun changes as the Moon moves around Earth. Although the same side of the Moon always faces us, the sunlit fraction we see grows and shrinks, producing the familiar sequence of phases.
The Eight Principal Lunar Phases
- New Moon – The Moon lies between Earth and the Sun, so the near side is dark and the Moon may be invisible from Earth.
- Waxing Crescent – A narrow sliver of light appears; the illuminated part is on the right for Northern Hemisphere observers.
- First Quarter – The right half of the Moon is illuminated; it appears as a half-moon.
- Waxing Gibbous – More than half of the near side is lit, leading up to full moon.
- Full Moon – The entire near side is illuminated and fully visible.
- Waning Gibbous – The Moon begins to lose illumination on the right (Northern Hemisphere).
- Third Quarter (Last Quarter) – The left half of the Moon is illuminated; another half-moon phase.
- Waning Crescent – Only a thin sliver of light remains on the left before the cycle returns to New Moon.
Note: The apparent side that is illuminated reverses between the Northern and Southern Hemispheres (i.e., what appears lit on the right in the north appears lit on the left in the south).
Source: NASA lunar phase data and Daily Moon Observations.
