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Watch for young moon and Venus

Fresh from Sunday’s eclipse, the moon is now waxing, visible after sunset, sweeping up past Venus and Mars in the evening twilight sky.

Martin Marthadinata in Surabaya, a port city on the Indonesian island of Java, captured this image of Venus and the moon on February 28, 2017.

A waxing crescent moon – sometimes called a young moon – is always seen in the west after sunset. The late February/ early March 2017 young moon appears nears Venus and Mars.

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.

But a waxing crescent moon is far enough away from that Earth-sun line to be visible near the sun’s glare – that is, in the west after sunset. Watch for the moon near the planets this week!

At the end of February and the beginning of March, the waxing crescent moon swings by the planets Venus and Mars. Do you have binoculars? Then seek for the planet Uranus in the same binocular field with Mars! Read more.

And, by the way, if you could view Venus through a telescope now, you’d find it in a crescent phase, too. It’s look just like a tiny crescent moon. Telescopes reveal Venus as a crescent in our sky now because the planet is about to sweep (more or less) between the Earth and sun at inferior conjunction on March 25. Hence, the day side of Venus is mostly aimed away from our direction now, and Venus will continue to wane in phase until it passes inferior conjunction and enters the morning sky.

As for the moon, although there are seasonal effects, in general a waxing moon is seen one day to several days after new moon. It’s always seen in the evening, and it’s always seen in the west. On these days, the moon rises one hour to several hours behind the sun and follows the sun across the sky during the day. When the sun sets, and the sky darkens, the moon pops into view in the western sky.

The moon is now waxing toward first quarter. Next first quarter moon will be March 5, 2017 at 11:32 UTC.

Next full moon is March 12 at 14:54 UTC.

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2017 started out with a beautiful waxing crescent moon. This day-lapse composite image combines the earthshine moon from New Year’s Day with the crescent moon from the following day. A wide-field image with Venus at sunset and more information on how to make day-lapse images is available from Robert Pettengill of Austin, Texas.

Note that 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.

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.

The pale glow on the darkened portion (night side) of a crescent moon is called earthshine. Is 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?

Steven Arthur Sweet of Lunar101-MoonBook caught earthshine on the February 27, 2017 moon. He wrote: “Thin waxing crescent 1-day young moon in Pisces, captured from Centennial Hill, Toronto.”

As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.

Four keys to understanding moon phases

Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase

Check out EarthSky’s guide to the bright planets.

Deborah Byrd