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Watch for a young moon after sunset

The hunt for a young moon – a thin crescent moon visible in the west after sunset – has become a favorite activity for many of EarthSky’s moon-watching fans. Although the new moon came to pass on August 30, 2019, we’re expecting a number of people around the world to catch the whisker-thin waxing crescent after sunset August 31. If you miss the exceedingly slender young moon at dusk on August 31, give it another try on September 1, 2 or 3. Look west, shortly after sunset.

It’s best to have an unobstructed horizon in the direction of sunset for any young moon quest. If possible, find a hill or balcony to stand on, enabling you to peek just a little farther over the horizon. Binoculars come in handy, too, especially around August 31 and September 1, because it’s possible for the bright evening twilight to bleach out the tiny, ghostly lunar crescent from naked eye visibility.

Very thin crescent moon in western twilight after sunset with feathery pink clouds.
View larger. Congratulations to Jenney Disimon, who caught the young moon after sunset August 31, 2019, from Sabah, North Borneo. Thank you, Jenney!

For most of the world, the moon will be over one day old (more than 24 hours past new moon) as the sun sets on August 31. The worldwide map below shows you the line of sunset running through eastern Asia when it’s exactly one day (24 hours) past new moon on August 31, at 10:37 Universal Time (UTC). At this juncture, the moon is about 14 degrees (28 moon-diameters) east of the setting sun.

It’s usually quite difficult to see a young moon that’s less than 24 hours old. For Japan and Australia on August 31, the young moon will set roughly 50 minutes after the sun, so it may be hard to spot this skinny moon with the eye alone.

Visit Sunrise Sunset Calendars to find out when the moon sets in your sky, remembering to check the moonrise and moonset box.

Rolled-out flat map of Earth with lighted half from South America to east Asia.
The worldwide map shows the line of sunset (running across Asia) one day after new moon (August 31 at 10:37 UTC). By the time the line of sunset crosses Africa and Europe, the moon will be about seven moon-diameters farther east of the setting sun that it was at sunset in eastern Asia. When the line of sunset reaches North America, the moon will be about 18 moon-diameters farther east of the sun than it was in eastern Asia. Image via EarthView.

By the time the line of sunset reaches Africa and the Middle East on August 31, the moon will be 1 1/4 days old (on August 31 at 16:37 UTC). The moon will also be about seven moon-diameters farther from the setting sun than six hours previously (when it was one day old on August 31 at 10:37 UTC). That means a wider crescent (2.4 percent illuminated versus 1.5 percent illuminated), which, in addition, stays out longer after sunset.

By the time the line of sunset reaches North America on August 31 (local time), the young moon will be about one day and 15 hours old (on September 1 at 01:37 UTC). So, in North America, the young waxing crescent will be about 4 percent illuminated at sunset August 31, and the moon will be some 18 moon-diameters farther away from the setting sun than 15 hours previously (when the moon was one day old on August 31 at 10:37 UTC). Yes, the Americas have the big advantage for catching the young moon after sunset August 31.

Very thin young moon in western sky streaked with red and orange after sunset.
View larger at EarthSky Community Photos. | Ray Mandra from Brewster, NY, USA, caught the young moon after sunset August 31, 2019, with vivid sunset colors adorning the horizon. Thank you, Ray!

However, the world as a whole enjoys an advantage for this particular young moon hunt. The closest new moon of the year fell on August 30, 2019. With the new moon coming so close to Earth, the moon is now orbiting Earth at a maximum speed. Hence, the young moon is moving away from the setting sun on the sky’s dome at a faster clip than it usually does.

Read about the year’s closest new supermoon on August 30

Normally, the Southern Hemisphere has the advantage over the Northern Hemisphere for catching a young moon in late August or September. It is now winter in the Southern Hemisphere, and, as a general rule, late winter is favorable for a young moon hunt. In late winter, the ecliptic – the moon’s monthly pathway – hits the sunset horizon at a steep angle. Because the young moon is generally higher up at sunset in late winter, it tends to stay out longer after sundown than at other times of the year.

It is now late summer in the Northern Hemisphere, and, generally, late summer is not so favorable for catching a young moon. The ecliptic hits the sunset horizon at a shallow angle in late summer, tending to bury the young moon in the glare of evening twilight.

Very thin orange crescent in deep reddish purple sky with a bright dot to its right.
A very young moon and Jupiter on September 2, 2016, captured by Greg Hogan in Kathleen, Georgia.

Fortunately for us northerners, this particular young moon swings a maximum of five degrees (10 moon-diameters) north of the ecliptic. That pretty much cancels out the Northern Hemisphere’s disadvantage and the Southern Hemisphere’s advantage, giving the Northern Hemisphere a better-than-usual opportunity for catching a late-summer young moon.

By the way, that bright star close to the young moon is Spica, the constellation Virgo’s one and only 1st-magnitude star. This star will probably be much easier to spot with the eye alone from the Southern Hemisphere. Visit Heavens-Above to know which constellation of the zodiac is presently behind the moon.

Wherever you may reside worldwide, try catching the young moon after sunset in late August or early September. For a special treat, check out the earthshine softly illuminating the dark side of the moon with either the unaided eye or binoculars. Day by day, watch the illumined portion of the lunar crescent grow, and for the moon to stay out longer after sundown.

Bottom line: Look for the young moon on August 31, 2019, through the first days of September.

August 31, 2019
Sky Archive

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Bruce McClure

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