A slender crescent Moon is a beautiful and inspiring sight. December and January offer several opportunities to see these exceptional slices in the sky.
When it comes to seeing a young lunar crescent, my personal best is a 21.5-hour-old Moon. That's a far cry from the record, but what a sight. The Moon was fine china, so fragile you might crack it with the slightest touch. Crater shadows took little bites out of the delicate lunar arc, adding to the exquisite view.
This December and in the coming months, we'll have several opportunities to catch youthful crescents at dusk or senior ones at dawn. A few of these will be extremely challenging, others easier but just as remarkable to behold.
A day-old crescent isn't too difficult to see and a worthy goal for the naked-eye observer. The visibility of young (or old) crescents has much to do with the angle the Moon's path makes to the horizon.
The Moon basically follows the ecliptic, the same path traveled by the Sun and planets. From mid-northern latitudes in late summer and fall, the ecliptic tilts upward at a very shallow from the sunset horizon, so thin crescents barely escape the solar glow and are difficult or impossible to see.
From winter through mid-spring, however, the lunar byway tilts upward at an ever-steeper angle from the western horizon, placing the Moon higher up in the sky and offering us a better view. The opposite situation rules at dawn, with summer and fall the best times to seek the waning crescent.
Because the Moon's orbit is tipped relative to the plane of Earth's orbit, it can range up to 5° north or south of the ecliptic. If the crescent occurs around the northern extreme, visibility is improved for mid-northern latitude observers and similarly for southern observers at its southern extreme.
Essential to seeking young and old crescents is knowing the date of New Moon and time of sunset / sunrise. This month, new Moon occurs at 1:30 a.m. Eastern Standard Time (6:30 UT) December 18th. Because a crescent's age depends on your location, in this article we'll feature its visibility across North American time zones. I ask forgiveness from European and other observers and encourage you to use the listed times of new Moon at the end this article to determine your own best crescents.
On the December 17th, the morning prior to new Moon, observers in the central and southern U.S. might see a micro-thin waning crescent just 2° to 3° high in the southeastern sky 35 to 20 minutes before sunrise. From the eastern U.S., the Moon would be just 18.5 hours before new phase. From the Central time zone, 17.5 hours; 16.5 from the Western states; and 15.5 from the West Coast. The farther east you live the easier it will be to see the early new Moon. To attempt this tantalizing challenge, you'll need clear, haze-and-cloud-free skies, a completely open view to the southeast, and a pair of binoculars. If you have access to a mountaintop or a tall hill, all the better.
Prefocus the binoculars at infinity on a bright star earlier that night or point them at the planet Jupiter, well up in the southeastern sky in morning twilight. Start your sweeps to the right of the brightest twilight glow (where the Sun will soon rise) to seek the skinny curve of the lunar crescent. Once you've found it, slowly lower the binoculars while focusing your gaze at the Moon's location to see if you can discern it without optical aid.
For a shot at the evening crescent on December 18th, find a location with a view as close to the southwestern horizon as possible and start searching about 20–25 minutes after sundown. Here are the Moon's ages (give or take) depending on where you live — East Coast: 15.5 hours; Central: 16.5 hours; Mountain: 17.5 hours; and West Coast: 18.5 hours.
During both events, the Moon's distance from the Sun varies from about 7.5° to 8.5°. Research done by Louay J. Fatoohi and his colleagues at the University of Durham (paper here) have shown that when the Moon is fewer than 7.5° from the Sun, it's impossible to see due to atmospheric extinction, physiological factors, and the shrinkage of the crescent's length caused by crater and mountain shadows clipping the ends. In December, the waning crescent will be an easier sight for the eastern half of the country with the evening crescent easier for the western half.
Other factors influencing the Moon's visibility include perigee timing. If the crescent occurs around the time of perigee (closest to the Earth), it will move up and away from the Sun into the evening sky more quickly, enhancing its visibility compared to the more "sluggish" apogee Moon.
The record for the youngest Moon sighted with the naked eye goes to amateur astronomer Steven James O’Meara, who nabbed a 15 hour-32 minute crescent in May 1990. Mohsen G. Mirsaeed of Tehran broke the record for youngest Moon ever seen with optical aid on September 7, 2002. He observed from a mountain site using giant 40×150 binoculars and held a razor slice of crescent in view for one minute. At the time, the Moon was just 11 hours, 40 minutes past new and 7.5° from the Sun.
The ultimate record was set on July 8, 2013, by French astrophotographer, Thierry Legault, who photographed the moment of new Moon. The Moon lay just 4.4° south of the Sun at the time, so its extreme northern edge caught enough sunshine to show as a crescent. Only the camera recorded the historical moment as the sky was much too bright to see the Moon even through a telescope.
Keep the following list of exceptionally young Moons handy, so you can try again on other occasions. It's one thing to set a new record for yourself, but in doing so, you'll witness one of the sky's most inspiring sites — a barely-there Moon.
Below is a list of sub-24 hour crescent moons to watch for across North American time zones from mid-northern latitudes (default is 40° N). To help in determining exactly where to look for the evanescent sight in your local landscape, I recommend the Photographer's Ephemeris app for Android and iPhone. You can also create realistic simulations of the Moon's phase and position with a free sky-mapping program like Stellarium.
- New Moon, January 16, 9:18 p.m. EST (2:18 UT January 17). Excellent evening window 30–40 minutes after sunset on January 17th in the southwestern sky. The Moon's age East Coast to West Coast will be 20 hours to 24 hours. This is a great chance to spot a sub-24-hour Moon! Don't forget your camera 🙂
- New Moon, February 15, 4:06 p.m. EST (20:06 UT). No sub-24-hour Moon visible morning or evening.
- New Moon, March 17, 9:14 a.m. EDT (13:14 UT). No sub-24-hour Moon visible morning or evening.
- New Moon, April 15, 9:59 p.m. EDT (1:59 UT April 16). The viewing window is 20–30 minutes after sunset on April 16th for the western sky. The Moon's age East Coast to West Coast will be 21.5 hours to 24.5 hours.
- New Moon, May 15, 7:49 a.m. EDT (11:49 UT). No sub-24 Moon visible morning or evening.