Young moon: can you see one under 24 hours old?
New moon – when the moon will be between the Earth and sun – comes about every four weeks. That means the next evening you have an opportunity to spot an exceedingly young moon. By the way, seeing a moon within a day of new phase is very rare. At such times, the moon is still close to the sun along our line of sight. And its lighted portion turns almost entirely away from us. Whether you’ll see a very young moon depends on where you are on Earth’s globe, and on your sky conditions.
Catching a young moon
What’s the youngest moon it’s possible to see?
Definitely, it’s rare to see a moon within about 24 hours of the new phase. But it turns out, if you use optical aid, you can see the moon all the way until the moment of new moon. However, always avoid looking directly at the sun!!
On July 8, 2013, a new record was set for the youngest moon ever photographed (see photos on this page). Thierry Legault – shooting from in Elancourt, France – captured the July 2013 moon at the precise instant it was new. Or most nearly between the Earth and sun for this lunar orbit. Legault’s image (below) shows the thinnest of lunar crescents, in full daylight, at 7:14 UTC on July 8, 2013. Legault said on his website:
It is the youngest possible crescent, the age of the moon at this instant being exactly zero. Celestial north is up in the image, as well as the sun. The irregularities and discontinuities are caused by the relief at the edge of the lunar disk (mountains, craters).
Are you likely to see a young moon with your eye alone?
How young a moon you can expect to see with your eye depends on the time of year and on sky conditions. It’s possible to see the youngest moons – the thinnest crescents, nearest the sunset – around the spring equinox.
When Legault captured the image above, the sun and moon were separated only 4.4 degrees. Or about 9 solar diameters on the sky’s dome. It is extremely difficult, and risky, to try to capture the moon at such a time. Because bright sunlight will drown out the sight of our companion world. And there is also a risk of unintentionally glimpsing the sun and thereby damaging your eyesight.
That’s why Legault used a special photographic setup to capture this youngest possible moon. He wrote:
In order to reduce the glare, the images have been taken in close infrared and a pierced screen, placed just in front of the telescope, prevents the sunlight from entering directly in the telescope.
The record for seeing a very young moon
A longstanding, though somewhat doubtful, record for youngest moon seen with the eye is by two British housemaids. They said they saw the moon 14 3/4 hours after new moon in the year 1916.
Stephen James O’Meara achieved a more reliable record in May 1990. When he saw the young crescent with the unaided eye 15 hours and 32 minutes after new moon.
The record for youngest moon spotted with the eye using an optical aid passed to Mohsen Mirsaeed in 2002, who saw the moon 11 hours and 40 minutes after new moon.
But Legault’s photograph at the instant of new moon? That record can only be duplicated, not surpassed.
Tips for observing very young moons
Young moons are located some distance east of the sun on the sky’s dome (because the moon always moves eastward in orbit). Young moons appear to our eye as exceedingly slim crescents. And likely illuminated by earthshine, seen low in the western sky for a brief interval after sunset.
No matter where you are, remember to wait until the sun has completely set before scanning the horizon with optical aid! You’ll also need a flat, clear horizon to the west. Start looking shortly after the sun disappears. So, when bright twilight still fills the western sky look for the infant moon that’s barely illuminated!
And, of course, optical aid enhances your young moon possibilities even more.
Bottom line: Occasionally you get the chance to look for a very young moon, less than 24 hours old. Look just after sunset.