Catch the Conjunction!

Take a moment from your busy day to step outside after sunset tonight and the next few nights and check out the close conjunction of Venus and Jupiter in the western sky.  They make quite a pretty sight in the gathering twilight. I heard someone describe them as “hugging in the sunset” and that’s a very poetic way to see them.

“Conjunction” is an astronomy term that means “two objects look fairly close together in the sky”.  The formal definition is “when two objects in the sky have the same right ascension or ecliptical longitude when observed from Earth.” These astronomical events can include specific bright stars, as well, so occasionally you might see one or more of the planets in conjunction with a star such as Spica (in Virgo) or Regulus (in Leo).

What’s Really Happening?

As planets orbit the Sun (and as the Moon orbits Earth), they appear against a backdrop of stars, and occasionally other planets are in the view, too.  Think of it like being on a merry-go-round and looking out at the scenery as it goes by. People standing near the carousel appear against a backdrop of other people or trees or parking lots or whatever is out there.  They may all look close together, but in reality, they’re not. This is because we live in a 3D universe where objects are distributed throughout space.  From your perspective, however, they seem to be close together.

So, how far apart are they?  Right now Venus is about  670,198, 462 kilometers (416,442,017 miles) from Jupiter. (That’s 4.48 times the distance from Earth to the Sun.) If one of the planets happened to be in conjunction with the star Regulus, they would be 77.6 light-years apart! So, conjunctions are something of an optical illusion, collapsing the reality of space between them.

Conjunctions can happen on other worlds, and someday when we’re all living on Mars, we’ll be able to see events like this one that include Earth in the view. Until then, however, let’s make the most of the view from our planet! The planets are visible right after sunset and will slowly move toward the western horizon over the next few hours. Take out your telescope or binoculars to get a more detailed look at Jupiter. Happy gazing and clear skies!