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.
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.
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.
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.
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.