How many of you have been watching the dazzling planet Venus – third-brightest celestial object, after the sun and moon – in the west at dusk and nightfall? If you haven’t seen it yet, just look in the sunset direction for this brilliant beauty to pop out some 45 minutes to an hour after the sun goes down. People with excellent vision might see Venus earlier, almost immediately after sundown.
And while you’re out there gazing at the moon and Venus, be aware of this. There are two other worlds in the west after sunset now.
First, look for Mercury, below Venus. Will you see Mercury? Maybe. It’s not as bright as Venus, and it’s closer to the sunset glare. You’ll need to look for very shortly after the sun goes down. Read more.
The third planet is Neptune. It’s very close to Venus on late January 2020 evenings, but not visible to the eye alone. On January 27, 2020, Venus and Neptune will stage the closest conjunction of any two planets this year. Read more.
So Mercury … maybe. Neptune … for those with telescopes. Meanwhile Venus and the moon will be easy to see. The picturesque sky scene begins on January 26, when the young moon will come into view close to the western horizon, below Venus. That’ll be a sweet scene to catch. Especially on January 26, don’t dally. The whisker-thin waxing crescent moon will set before nightfall on that date. In fact, from some places worldwide, you might need binoculars to tease out the lunar crescent from the glare of evening twilight on the 26th. No matter where you are on Earth, though, given an unobstructed horizon and clear skies, you shouldn’t have any trouble spotting the young moon at dusk/nightfall after the sun sets on January 27 or 28.
Want to know when the moon sets in your sky? Click on this Moonrise and Moonset Calculator.
From the Southern Hemisphere, the ecliptic (green line on our chart) will be slanted from upper right to lower left. Use Stellarium online to get your location’s precise view.
Will you spot Mercury? On all of these evenings – January 26, 27, 28 and 29 – use the lit side of the lunar crescent to spot Mercury, the innermost planet of the solar system. The crescent will be pointing to Mercury, which is just now coming into view after sunset. You’ll likely need binoculars to spot it at evening dusk in late January 2020. Some people assume Mercury is very faint; that’s not so. Mercury is brighter than a 1st-magnitude star; it just seems faint because we nearly always see it against a bright twilight background.
Mercury will reach its greatest elongation from the sun on February 10, 2020. Use binoculars to spot Mercury all the sooner after sundown. Then try to spot it without your binoculars. Visit timeaddate.com and enter your location to find out when Mercury sets in your sky.
At this evening apparition of Mercury, the Northern Hemisphere enjoys a more favorable view than the Southern Hemisphere. From temperate latitudes in the Southern Hemisphere, Mercury will likely be particularly difficult to see, because this world sits deeper in the glare of evening twilight and sets sooner after sunset.
The Venus-Neptune conjunction on January 27, 2020. As you enjoy the moon and Venus on these late January evenings, be aware that Venus, the sky’s brightest planet, is now paired up with Neptune, the sky’s faintest planet. Neptune is the most distant major planet in our solar system. It’s the only solar system planet that you absolutely cannot see without an optical aid. This world is some six times fainter than the faintest star that’s visible to the unaided eye.
So you won’t see Neptune with the eye. But amateur astronomers with small telescopes have had them trained on Venus for some time, watching for Venus and Neptune to stage the closest planetary conjunction of the year on January 27, 2020. At conjunction, these two worlds are spaced only 1/12th of one degree apart. Photo opportunity indeed (for those with telescopes)! For reference, the angular diameter of the moon spans about 1/2 degree, which is some six times greater than the tiny gap between Venus and Neptune.
Given that Venus outshines Neptune by about 60,000 times, it might be hard to glimpse Neptune in Venus’ glare at conjunction even with an optical aid. Venus will also be stunningly close to the 4th magnitude star Phi Aquarii at this time. Don’t mistake Phi Aquarii for Neptune. Phi Aquarii, though rather faint, is a good 30 times brighter than Neptune and can be seen by the eye alone on a dark night.
For many of us, it’ll be easier to view Neptune with an optical aid several days to a week after the January 27 Venus/Neptune conjunction. Venus will have moved away from Neptune, yet Neptune and the star Phi Aquarii will remain close together. This dim star will allow you locate Neptune, absent the glare of Venus.
Watch for earthshine, too. As you enjoy the lunar crescent on these late January 2020 evenings, note the soft glow of earthshine on the darkened portion of the moon. A moon with earthshine is not a moon in eclipse; no shadow or world in space is obscuring any other. Instead, you’re simply seeing the nighttime side of the moon, and, as it happens, the lunar night is covered over with earthshine: sunlight reflected from Earth to the moon. You know how a bright full moon can light up an earthly landscape? It’s the same on the moon, where a nearly full Earth shines now in the lunar night sky. On the moon, though, it’s earthlight that illuminates the scene. It’s that same earthlight (or earthshine, as we earthlings call it) you’re seeing on a waxing crescent moon.
Bottom line: After sunset on January 26, 27 and 28, 2020, watch for the young moon and planet Venus in the west at dusk and nightfall. Use the lit side of the moon to locate Mercury, the innermost planet. If you have a telescope, use Venus to locate Neptune, the farthest planet.