Go young moon hunting in late October

Please be mindful that it’ll be considerably easier to spot the young moon after sunset on October 29 than on October 28. However, some young moon aficionados have shown a uncanny knack for catching a tiny crescent that’s all but invisible in the western evening twilight. On October 28, the extremely-thin lunar crescent sits low in the sky at sunset and then follows the sun beneath the horizon shortly thereafter. In short, don’t be too surprised if you miss the moon after sunset October 28!

Click here to find out the moon’s setting time in your sky, remembering to check the moonrise and moonset box.

It is difficult to catch any young moon that’s less than one day (24 hours) after new moon, and nearly impossible to spot one that’s less than 18 hours after new moon. The new moon comes to pass on October 28, 2019, at 3:38 Universal Time, at which juncture the moon leaves the morning sky to enter the evening sky. By the time that sunset comes to the West Coast of North America on October 28, 2019, the moon will be 21 hours old (21 hours past new moon). See worldwide map below. You’ll have a better chance of spotting the young moon on October 28 from the North American Pacific Coast than at more easterly longitudes (Eastern United States, South America, Europe, Africa and Asia). Nonetheless, it’ll still be a big challenge, as the pale and whisker-thin crescent sets well before nightfall.

The sun sets over the North American Pacific Coast 21 hours after new moon.

As the sun sets on October 28, 2019, near the North American West Coast, the moon will be 21 hours past new moon. As the sun sets at more easterly longitudes (Eastern United States, South America, Europe, Africa, Asia, Australia and New Zealand), the young moon will be younger yet and more difficult to see.

All else being equal, a young moon is easier to spot on a spring evening than an autumn evening. That’s because the tilt of the ecliptic – the moon’s approximate path in front of the constellations of the zodiac – is steep to the sunset horizon in spring but shallow in autumn.

It’s now spring in the Southern Hemisphere and autumn in the North Hemisphere, so normally the Southern Hemisphere enjoys the advantage. Yet, this October new moon is nearly at its maximum distance north of the ecliptic, which pretty much cancel’s out the Southern Hemisphere advantage and the Northern Hemisphere’s disadvantage.

The slender crescent moon joins up with the planets Venus and Mercury.

The moon joins up with Venus and Mercury as seen from Cape Town, Africa, at dusk October 29, 2019. The steep tilt of the ecliptic gives the Southern Hemisphere a big advantage over the Northern Hemisphere for catching the planets Mercury and Venus after sunset.

But the Southern Hemisphere definitely has the ringside seat for catching the inferior planets Mercury and Venus after sunset, while we at northerly latitudes are relegated to the bleachers. Mercury resides to the south of the ecliptic whereas Venus aligns with the ecliptic, so there are no mitigating factors for us at northerly latitudes. In a nutshell, the farther south you live, the longer that Mercury and Venus stay out after sunset. Here are the approximate setting times for these planets at various latitudes for the next several days (presuming an absolutely level horizon in the direction of sunset).

35 degrees north latitude
Mercury sets a bit less than 1 hour after the sun
Venus sets about 1 hour after the sun

Equator (0 degrees latitude)
Mercury sets a bit more than 1 1/3 hours after the sun
Venus sets a bit less than 1 1/3 hours after the sun

35 degrees south latitude
Mercury sets nearly two hours after the sun
Venus sets over 1 1/2 hours after the sun

Click here for a sky almanac that gives you the setting times of the planets in your sky.

Two more bright planets light up the evening sky, both of which stay out till after nightfall. The brighter of the two is Jupiter, the 4th-brightest celestial object to light up the sky, after the sun, moon and Venus, respectively. Watch for the moon to meet up with the dazzling planet Jupiter around October 30 and 31, and to rendezvous with Saturn in early November.

Young moon, Jupiter and Saturn at dusk.

Day by day, watch for a wider lunar crescent to climb higher up at sunset and to stay out longer after dark.

Day by day, watch for a wider lunar crescent to climb higher up at sunset and to stay out longer after dark. In the next few days, you may note that the dark side of the moon is covered over by the soft glow of earthshine – sunlight reflected from Earth to the moon, and then from the moon back to Earth.

By the way, when Mercury goes back into the sun’s glare – and passes between the Earth and sun – it will cross directly in front of the sun, creating what’s called a transit of Mercury. Although much more common than transits of Venus, a transit of Mercury happens only 14 times in the 21st century (2001 to 2100). Read more about the Mercury transit on November 11, 2019.

Bottom line: To maximize your chances of catching the young moon after sunset in late October 2019, find an unobstructed horizon in the direction of sunset. If you’re in the Northern Hemisphere, binoculars might come in handy!

Bruce McClure