On June 30 and July 1, the two brightest planets in our night sky, Venus and Jupiter, will appear exceptionally close in the western sky after sunset. Their closest approach, at about 1/3 of a degree, will appear less than the size of the nearly full Moon rising in the east at the same time. (The moon's apparent diameter is about 1/2 of a degree. That’s about the width of pencil held at arm's length. Try it!) Though the event is technically an appulse, when planets appear to pass each other in the sky, we call it a conjunction.
You may think the brighter of the two would be the enormously more massive and nearly fully illuminated gas giant Jupiter, but it’s actually the crescent of our moonless, CO2 drenched, terrestrial neighbor Venus, which is much closer, both to the Sun and to us. After the Sun and Moon, Venus is the brightest object in the night sky, followed by Jupiter.
Venus, Jupiter, and Mercury on May 26, 2013. (Adam Esposito/Exploratorium)
But what’s so special about conjunctions? I like conjunctions because they’re one of the best and simplest chances you have to experience the layout of our solar system. By tilting your head and eyes parallel to the ecliptic, your spatial perception of our orbiting racetracks seems to "click in," and the depths, distances, and appearances of the sky's brightest objects become easier to fathom. Instead of being hobbled by the fallacy of the nightsky as "pinpoints of light on a dome," conjunctions and appulses (also: occultations and transits) make space feel more...spacious.
So grab a chair and enjoy the beginning of the warm skywatching season with this brilliant pair in the west.