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Moon and Venus December 2 to 5

UPDATE DECEMBER 4, 2018: Venus has been been near the waning moon these past few mornings (photos here), and it’ll be near the moon today and December 5, too. We’ve also been hearing from people who have seen the planet Mercury below the moon and Venus! To see them all, you’ll need a clear sky to the east before sunrise. The moon and Venus are always the brightest and second-brightest celestial objects in the night sky. Plus, Venus has been shining near its maximum brightness for this morning apparition, with its greatest illuminated extent falling around December 2.

The planet Mercury is much fainter, lower in the sky than Venus, near the exceedingly thin crescent moon on Wednesday morning, December 5. To see them on this morning, unless you’re eagle-eyed and have a very clear sky, you might need binoculars. Mercury is brightening day by day now. It’s also coming up earlier by the day. By the middle of December, Mercury will be a fine morning object. It would be lots of fun to spot it now and watch it brighten!

The moon and Venus are so bright and beautiful that you’ll easily spot them at morning dawn. And, if you’re willing to get up an hour or two before sunrise, you can also see the bright star Arcturus to the north (left) of the moon and Venus, and the star Spica close to Venus.

The December 3, 2018, waning moon, planet Venus and bright star Spica via Lunar 101-Moon Book.

If you peered at Venus through a telescope now, you’d find it in a waxing crescent phase. That’s because Venus passed between us and the sun on October 26, and its lighted half – or day side – is still facing mostly away from us.

In early December 2018, meanwhile, the moon is waning, and the phase of the waning crescent moon and waxing crescent Venus are almost identical. Both worlds are now showing us disks that are about one-quarter (25 percent) illuminated by sunshine. If you have a telescope, remember … you’ll get a crisper telescopic view of Venus’ phase at dawn, when this brilliant world has climbed higher above your horizon and its glare has been reduced by the breaking day.

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Venus in the predawn Tucson, Arizona, sky on November 27, 2018. Eliot Herman wrote: “Venus is currently about as bright as it will be for this cycle, glowing in the eastern morning sky. Venus is amazingly bright! Crescent Venus inset captured with a Questar telescope, 50 mm lens and a Nikon D850.”

After December 4 and 5, the moon’s phase will continue to wane (get smaller) as the moon falls closer to the sunrise. New moon is December 7. Afterwards, the moon will go back to being in the evening sky.

And, as the moon pursues its faster cycle and endless orbit around our world, Venus will be racing ahead of Earth in orbit around the sun. Its phase will be waxing, as this world pulls ahead of us in its smaller, faster orbit, causing its illuminated or day side to slowly turn our way.

When Venus’ disk reaches its half-lit waxing quarter phase on January 6, 2019, this planet will be at its greatest elongation of 47 degrees west of the sun.

After Venus attains that milestone in the morning sky, this planet will begin slowly but surely sinking toward the sunrise. It’ll take many months to do this, as it moves ahead of us in orbit. Venus will finally pass more or less behind the sun from Earth – at what astronomers call superior conjunction – on August 14, 2019. At that juncture, Venus will transition out of the morning sky and into evening sky. See the diagram below.

Earth's and Venus' orbits

The Earth and Venus orbit the sun counterclockwise as seen from the north of the solar system plane. When Venus is to the east (left) of the Earth-sun line, we see Venus as an evening “star” in the west after sunset. After Venus reaches its inferior conjunction, Venus then moves to the west (right) of the Earth-sun line, appearing as a morning “star” in the east before sunrise.

Mercury and Venus are called inferior planets because they orbit the sun inside of Earth’s orbit. Although Venus is about twice Mercury’s distance from the sun, Venus is nevertheless the hotter of these two worlds. Climate does not depend on the sun alone but also on a planet’s atmosphere. Venus’ thick atmosphere creates a greenhouse effect that brings Venus’ surface temperature to 864 degrees Fahrenheit (462 degrees Celsius). Read more here.

Even though the moon and Earth are virtually the same distance from the sun, the moon’s daytime temperature is much hotter, and its nighttime temperature is much colder, than here on Earth. That’s because Earth has a protective atmosphere whereas the moon has no atmosphere of significance. Read more.

Bottom line: Will you see Mercury near the moon on Tuesday or Wednesday morning, December 4 or 5? It’s possible. If you don’t see it, try scanning with binoculars, low in the eastern twilight. If your sky is clear to the east before sunup, you’ll surely see bright Venus!

Bruce McClure

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