What's Up: December 2019 Skywatching Tips from NASA (VIDEO)

December 1, 2019 – What’s Up for December? Venus, Saturn, the crescent Moon and Mars make close passes at dusk and dawn throughout the month.

On December 1st, Jupiter, Venus, Saturn and the crescent Moon form a lineup at dusk. You’ll need a pretty clear view toward the horizon to see Jupiter, which is setting soon after the Sun these days. Look for an unobscured view toward the southwest about half an hour after sunset.

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NASA tips on things to see in the December sky. Credit: NASA/JPL-Caltech

In the middle of December, watch each evening from the 9th through the 13th, as Venus and Saturn just skim past each other, with brilliant, cloud-swaddled planet Venus rising higher in the sky each day. (Sky Chart)

Early risers can catch a glimpse of the Red Planet being visited by the slim crescent of the Moon on December 22nd and 23rd. To see them, look toward the southeast about 45 minutes before sunrise. You’ll see the Moon above Mars on the 22nd. By the 23rd, it’s moved below Mars and a bit toward the east. (Sky Chart)

At the end of December, you won’t want to miss a dazzling pair-up of Venus and the crescent Moon. On the 28th, look low in the southwest sky at dusk to find Venus hovering in twilight just above a slim lunar crescent. (Sky Chart)

What is a Conjunction?

When two or more stars or planets appear to come close together in the sky, it’s often referred to as a conjunction. By “close” we mean objects separated by no more than a few degrees, or a few finger widths. This is an informal use of the term conjunction; technically, a conjunction occurs when two objects have the same right ascension.

Since the stars are fixed and don’t move appreciably, it’s the monthly wanderings of the planets and the Moon that create these occasional groupings in the sky. Since the Moon orbits Earth every month, groupings of the Moon and one or more bright stars and planets are the most common sort of conjunction. They also occur between the Moon or planets and clusters of stars, like the Pleiades.

It’s worth noting that some of the motion of the planets in the sky is due to Earth’s own motion around the Sun rather than the planets’ motions themselves.

When two or more stars or planets appear to come close together in the sky, it’s often referred to as a conjunction. By “close” we mean objects separated by no more than a few degrees, or a few finger widths. This is an informal use of the term conjunction; technically, a conjunction occurs when two objects have the same right ascension.

Since the stars are fixed and don’t move appreciably, it’s the monthly wanderings of the planets and the Moon that create these occasional groupings in the sky. Since the Moon orbits Earth every month, groupings of the Moon and one or more bright stars and planets are the most common sort of conjunction. They also occur between the Moon or planets and clusters of stars, like the Pleiades.

It’s worth noting that some of the motion of the planets in the sky is due to Earth’s own motion around the Sun rather than the planets’ motions themselves.

This Month’s Moon Phases

Here are the phases of the Moon for December.

Chart showing phases of the Moon: 1st quarter Dec. 3, full Moon Dec. 11, 3rd quarter Dec. 18 and New Moon Dec. 25.
The phases of the Moon for December 2019. Credit: NASA/JPL-Caltech

The Earliest Sunset of the Year

For the Washington, DC area (and similar latitudes at least), the earliest sunset of the year will occur on Saturday, Dec. 7, 2019.

The length of a solar day varies throughout the year. Around the solstices the solar day is slightly longer than the 24 hour average that our clocks use. Because of this, the earliest sunsets of the year occur before the winter solstice and the latest sunrises of the year (ignoring Daylight Savings Time) occur after the solstice. For the Washington, DC area, the darkest evenings and earliest sunsets of the year will occur on the 13 days from Sunday, Dec. 1 through Friday, Dec. 13, 2019. Rounded to the minute, these sunsets will be at 4:46 PM EST across these dates.

Sky Charts

The sky charts presented here show a field of view of 90 degrees — that is, an area on the sky that goes from the horizon up to the top of the sky (also called the zenith).

Daily Guide

December 4

On Wednesday morning, Dec. 4, 2019, the Moon will appear half-full as it reaches its first quarter at 1:58 AM EST.

Wednesday night, Dec. 4, 2019, at 11:09 PM EST, the Moon will be at apogee, its farthest from the Earth for this orbit.

Sometime around the first half of December, 2019 (2019-Dec-06 16:26 UTC with 7 days, 22 hours, 54 minutes uncertainty), Near Earth Object (2016 XA2), between 127 and 284 meters (417 to 933 feet) in size, will pass the Earth at between 0.9 and 133.1 lunar distances (nominally 66.9), traveling at 28.76 kilometers per second (64,330 miles per hour).

December 7 – 8

Sometime on Saturday or Sunday, Dec. 7 or 8, 2019 (2019-Dec-07 20:32 UTC with 10 hours, 48 minutes uncertainty), Near Earth Object (2009 WY7), between 40 and 90 meters (132 to 295 feet) in size, will pass the Earth at between 2.9 and 90.2 lunar distances (nominally 37.7), traveling at 16.54 kilometers per second (37,000 miles per hour).

December 10 and 11

On the evenings of Tuesday and Wednesday, Dec. 10 and 11, 2019, bright Venus will appear less than two degrees from Saturn. Try looking in the southwest as evening twilight ends (around 5:50 PM EST for the Washington, DC area).

On Tuesday evening into Wednesday morning, Dec. 10 to 11, 2019, the bright star Aldebaran will appear near the full Moon. As evening twilight ends on Tuesday evening, Aldebaran will appear about 6.5 degrees below and to the left of the Moon in the east. By the time morning twilight begins on Wednesday morning, Aldebaran will appear about 2.5 degrees to the left of the setting Moon in the west-northwest.

December 12

The full Moon after next will be Thursday morning, Dec. 12, 2019, at 12:12 AM EST.

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