Astro Bob: Razor-thin moon complements Venus-Saturn conjunction

On Sunday, Jan. 22, at dusk, Venus and Saturn pair up in a close conjunction in the company of a slender moon.

Venus Saturn crescent
Venus and Saturn will be 0.4 degrees apart — two-thirds of the full moon's width — on Sunday evening, Jan. 22. While the pair should be a wonderful sight especially in binoculars, the nearby lunar crescent will make it even better. Find a place with an open view to the southwest and start watching about a half-hour after sunset. Saturn will become more obvious to the unaided eye as the sky darkens.
Contributed / Stellarium

Every star and planet in the eastern sky moves westward during the night because of Earth's rotation. Superimposed on this daily motion is something called seasonal drift. Over time, stars in the east drift westward. Months after their first appearance, they disappear in the glow of evening twilight, then return to the morning sky to begin the cycle anew.

Think of Orion. First visible in the east at dawn in August, this distinctive constellation slowly slips westward until it stands high in the southern sky at nightfall in January. By late April, the Hunter hovers low in the western sky and soon fades from view, lost in the twilight glow.

Now it's Saturn's turn to exit the stage. And lucky for us it does it with fanfare.

Orion seasonal drift
As the Earth revolves around the sun, stars and planets rise 4 minutes earlier each night, gradually sliding to the west over time. In this example, we see Orion at the same 10 p.m. time but in different months. In November Orion appears in the east, stands due south in January and tips westward in March. Seasonal drift is distinct from Earth's daily rotation which causes celestial objects to circle around the entire sky every 24 hours.
Contributed / Stellarium with additions by Bob King

Like Orion, the ringed planet has slowly drifted westward since the summer months. Right now it's only visible at dusk, setting just as the sky turns dark. Earth's orbital motion causes this gradual or seasonal drift of the stars and planets from east to west.

The constellations and planets slowly march from east to west across the sky during the year as Earth orbits the sun. In January we face Orion, so it appears high up in the southern sky. Two months later in March, Orion appears off to our right — to the west — and we face the constellation Leo instead.
Contributed / Bob King

As slower, outer planets like Saturn circle the sun, the faster Earth passes them up during our yearly, orbital journey. Earth also passes up the stars because they're so far away they appear motionless from our perspective.


It goes like this. First, a planet will appear ahead of us (in the eastern sky) just like a car we plan to pass on the freeway, then at our side (southern sky) as we pass it, and finally in the rear view mirror (west) after we zip by.

On Sunday evening (Jan. 22), before Saturn bids farewell, it will run almost directly into Venus. Not a real hit, of course, but the two will appear to nearly merge along the same line of sight. We say they're in conjunction. A conjunction is a temporary union of two celestial bodies and very pleasing to the eye.

Venus Saturn scope view
In a small telescope you'll be able to make out Saturn's rings and the gibbous phase of Venus. Both planets will fit in the same low-to-medium magnification field of view.
Contributed / Stellarium

Venus will be easy to spot low in the southwestern sky starting a half-hour after sunset. In binoculars you'll be able to make out Saturn to the upper right of the bright planet. As the sky gets darker, Saturn will show without optical aid. The difference between them is remarkable, with Venus beaming nearly 100 times as bright!

Both are covered in clouds, which are great reflectors of sunlight. Venusian clouds are not only whiter, but Venus is much closer to both the sun and Earth than Saturn, so it reflects brightly. Sunday night, we'll be 143 million miles from the Evening Star compared to 997 million miles for Saturn (143 million km and 1.6 billion km).

After Sunday night, the two will drift apart. Saturn continues its westward journey, moving deeper into the solar glare, while Venus moves the opposite direction — up and to the east. Venus defies seasonal drift because it's an inner planet. Not only does it move faster than the Earth, but its apparent distance from the sun is currently increasing as it swings to one side of its orbit from our perspective.

Crescent moon  1 day March 7_2019 CROP.jpg
This day-old crescent moon adds spice to the dusk sky in March 2019.
Contributed / Bob King

At the same time as the conjunction, look for the hair-thin crescent moon dangling below the pair. Try taking a photo with your cell phone. Twilight provides enough light to capture both bright celestial objects and a silhouetted foreground scene.

Only 1.3 days "old," the moon is barely out of the barn and will look as thin as if a spider spun it. Find a location with an unobstructed view to the southwest and plan the best time to be there using this sunset calculator . Then simply enjoy. Clear skies!

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at
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