Be The First On Your Block To See Venus

Try for Venus tonight if it’s clear. Find a place with a wide open view to the west and sweep back and forth just above the horizon with binoculars to find the planet. 20 minutes after sunset Venus stands just about 2° high in the west and 18° (two fists) to the lower right of the 2-day-old crescent moon. Click here to find the time of local sunset to plan your observation. Stellarium

Hey, look who’s back! Venus has spent a lot of time near the sun in the sky. But as the leaves drop and the trees go bare in the coming weeks, the planet returns to bring cheer to the evening sky. For now it’s very low in the west shortly after sunset. If you live in the U.S. you’ll need a cloudless western sky and binoculars to spot it. I’m itching for a first look later this week after the rains pass. Click here for your sunset time.

Piqui Díaz of Ezeiza, Argentina (near Buenos Aires, latitude 35° S) climbed up on her roof to capture this image of Venus perched momentarily atop a radio antenna minutes after sunset on Sept. 23. She used a cellphone and binoculars. Piqui Díaz

I recommend finding a location with a view as far down to the western horizon as you can get. Start looking about 10 minutes after sunset. The crescent moon has returned to the evening sky as well. Use it to help guide you to the planet. The moon can be helpful in another way. Once you focus it sharply in the binoculars Venus will also be focused. Focus is important. If you don’t do it, Venus will be a blob of light instead of a point and much more difficult to find. So look at the moon first and then slowly sweep back and forth along the horizon. The planet will be located just above the bright “sunset hump”, marking the location at the horizon where the sun just set.

You may not see Venus on the first try, but keep at it. If you check now and again you can be the first in your neighborhood to greet our sister planet this fall. I enjoy the modest challenge spotting Venus early presents. Planets are just fun to watch but seeing them under less than ideal circumstances hones our sky observing skills. We learn to see into the world, not just at it.

From mid-northern latitudes the path Venus follows (the ecliptic) makes a shallow angle to the horizon, so the planet hovers low in the west. Compare to the view from Bogota, Colombia (below). Stellarium

What makes Venus tricky right now is its small solar elongation. That just means it’s not far from the sun. No matter where you live on the Earth, the apparent distance of Venus from the sun is the same. A week ago, when its elongation was only 11° or about one fist to the east of the sun, equatorial and southern hemisphere observers made the first sightings of the planet about 10 minutes after sundown.

Now it our turn. Skywatchers in mid-northern latitudes needed to wait longer for Venus to move away from the sun’s glare. That has to do with the tilt or inclination of Venus’s path across the sky. The planets, moon and sun travel across the sky on a single highway called the ecliptic. In autumn, the angle the ecliptic makes to the western horizon at sundown is very shallow. Right now, Venus lies 13° (a little more than one fist) east of the sun, but because the angle it makes to the sun is so slight, it’s only about 3° high in the west 10 minutes after sunset.

Look at the difference the tilt makes in Bogota! There, Venus will stand twice as high above the western horizon tonight compared to the central U.S. Most of the 13° elongation “lifts” Venus above the sun instead of moving it off to the side as viewed from mid-northern latitudes. Stellarium

But in Bogota, Colombia, located just 5° north of the equator, the ecliptic makes a much steeper angle to the horizon. Most of that 13° goes toward elevation. In Duluth, Minn. (latitude 47° N) very little of it goes to elevation. From the diagram you can that most of it just increases the horizontal distance between Venus and the sun, not its altitude.

As Venus orbits the Sun interior to Earth’s orbit, its apparent distance from the Sun (and phase) changes. It’s currently on the other side of its orbit from Earth and appears near the sun in the sky. Wikipedia with additions by the author

We need altitude to see stuff. The higher up something is, the easier it is to spot. In the coming weeks and months as the apparent distance of Venus from the sun increases we’ll see the planet slowly rise higher in the western sky. The angle the ecliptic makes to the horizon will also steepen and loft Venus to the heights. A month from now the planet will still be low but obvious, and by Christmas it hang like an ornament above the forests and freeways of the planet, visible to all.

2 Responses

  1. I haven’t seen Venus with the unaided eye yet.
    Our Westchester (NY) Astronomers’ observing site at Ward Pound Ridge Park has a mostly clear western horizon. When I arrived at our Sat Sept 21 Starway to Heaven, I plunked down my 8-inch dob and mucked around near the western horizon until I spotted Venus. Venus was listed as 3 degrees above the horizon and the Sun as 3 degrees below (Mobile Astronomy Android app). Venus was 11 degrees to the upper left of the Sun at that time. Venus just looked like a tiny, very bright sparkle. Several people got to see Venus through the scope before it was obscured by distant clouds and set. (The 40mm 2-inch eyepiece helped a lot.)
    The inclination aspect is going to make Venus hard to find for those of us without a good western view. It will be a surprise to those who have a clearing and suddenly sight it. Contrast that with seeing our Moon so well this past month as its path had a large inclination in the morning sky (and will next month). bob kelly

    1. astrobob

      Yes, it certainly is a challenge at the moment, Bob. Binoculars should capture it, but it will be a few weeks before we see it naked-eye.

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