Tonight – January 18, 2018 – look for the slender young moon in the southwest sky at dusk. It’ll set shortly after the sun, at or around nightfall. If you miss the moon on January 18, try again on January 19. Day by day, the moon will move farther east of the setting sun, to appear higher up after the sun goes down.
But why stop there? Try catching earthshine on the dark side of the moon. Whenever the moon appears as a slender crescent in Earth’s sky, the Earth appears as an almost-full waning gibbous Earth in the moon’s sky. Earthshine is twice-reflected sunlight – sunlight reflected from the Earth to the moon, and then from the moon back to Earth.
On the average, the moon moves some 13o eastward per day in front of the backdrop stars of the zodiac. Meanwhile, as seen from Earth, the sun appears to move one degree eastward per day along the ecliptic. In other words, the moon moves an average 12o east of the sun daily. For reference, the angular diameter of the sun and moon span about one-half degree of sky. This movement of the moon on our sky’s dome is, of course, due to the moon’s motion in orbit around Earth.
The January new moon happened on January 17 at 2:17 Universal Time. For us in the United States, that translated to January 16 at 21:17 (9:17 p.m.) EST, 20:17 (8:17 p.m.) CST, 19:17 (7:17 p.m.) MST and 18:17 (6:17 p.m.) PST.
So, after sunset on February 19, the moon will be nearly two days old for us in the Americas.
At comparable latitudes in the world’s Eastern Hemisphere – Europe, Africa and Asia – the January 18 young moon will exhibit a thinner crescent hovering closer to the horizon. Click here for an almanac giving you the time of moonset in your sky.
Given an unobstructed horizon in the direction of sunset, and a clear sky, the thin waxing crescent moon will appear low in the sky and close to the horizon around one hour (or sooner) after sunset on January 18. Because the view is sometimes murky near the horizon, binoculars might come in handy for seeking the January 18 young moon near the sunset horizon.
Bottom line: Given an unobstructed horizon in the direction of sunset, and a clear sky, the thin waxing crescent moon should appear low in the sky and close to the horizon around one hour (or less) after sunset on January 18, 2018.