The moon has returned to the evening sky now. You’re likely to see it in the coming evenings. Astronomers call it a young moon – a waxing crescent – when the moon appears in the west shortly after sunset.
The moon was possible to see from all of North America last night, but very thin and tough to see from the U.S. East Coast.
As Earth spun under the sky yesterday evening, the moon was moving in its orbit, putting distance between itself and the sun on our sky’s dome. In other words, the moon was waxing larger. By the time Earth’s spin had brought the moon into view for California, the moon was a bit easier to see.
We received many photos of the moon on the evening of June 14. Submit your photo to EarthSky here.
Some people think a moon visible in the west after sunset is a rising moon. But it’s not; it’s a setting moon. All objects in our sky rise in the east and set in the west, due to Earth’s spin under the sky. When you see a waxing crescent, you know the Earth, moon and sun are located nearly on a line in space. If they were more precisely on a line, as they are at new moon, we wouldn’t see the moon. The moon would travel across the sky during the day, lost in the sun’s glare.
This week, for all of us around the globe, the waxing crescent moon is just off the Earth-sun line and so appears in the west after sunset.
There are two planets in the west after sunset now, and the moon appears near them. The moon has already swept past the planet Mercury, which is now very low in the west after sunset. It’ll be passing Venus next. Watch for the moon and Venus on the evenings of June 15 and 16.
By the way … a crescent moon has nothing to do with Earth’s shadow on the moon. The only time Earth’s shadow can fall on the moon is at full moon, during a lunar eclipse. There is a shadow on a crescent moon, but it’s the moon’s own shadow. Night on the moon happens on the part of the moon submerged in the moon’s own shadow. Likewise, night on Earth happens on the part of Earth submerged in Earth’s own shadow.
What many think is Earth’s shadow on a crescent moon is really something else. It’s earthshine, the pale glow on the darkened portion (night side) of a crescent moon. It’s caused by light reflected from Earth’s day side onto the moon. After all, when you see a crescent moon in Earth’s sky, any moon people looking back at our world would see a nearly full Earth. Read more: What is earthshine?
Because the waxing crescent moon is nearly on a line with the Earth and sun, its illuminated hemisphere – or day side – is facing mostly away from us. We see only a slender fraction of the day side: a crescent moon. Each evening, because the moon is moving eastward in orbit around Earth, the moon appears farther from the sunset glare. It is moving farther from the Earth-sun line in space. Each evening, as the moon’s orbital motion carries it away from the Earth-sun line, we see more of the moon’s day side. Thus the crescent in the west after sunset appears to wax, or grow fatter each evening.
Bottom line: The June 2018 young moon has returned to the evening sky. Photos and video from the EarthSky community here.
Check out EarthSky’s guide to the bright planets.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.