The year’s finest conjunction is upon us. Chances are you’ve been watching Venus and Jupiter at dusk for some time.

Like two lovers in a long courtship, they’ve been slowly approaching one another for the past several months and will finally reach their minimum separation of  just over 1/4° (half a Full Moon diameter) Tuesday evening June 30.

The view facing west-northwest about 50 minutes after sunset on June 30 when Venus and Jupiter will be at their closest. If bad weather moves in, they’ll be nearly as close tonight (June 29) and July 1.  Two celestial bodies are said to be in conjunction when they have the same right ascension or “longitude”and line up one atop the other. Source: Stellarium

Most of us thrill to see a single bright planet let alone the two brightest so close together. That’s what makes this a very special conjunction. Conjunctions are actually fairly common with a dozen or more planet-to-planet events a year and 7 or 8 Moon-planet match-ups a month. It’s easy to see why.

From our perspective in the relatively flat plane of the Solar System we watch the planets cycle around the Sun projected against the backdrop of the zodiac constellations. They – and the Moon – follow the ecliptic and occasionally pass one another in the sky to make for wonderful conjunctions. Credit: Bob King

All eight planets travel the same celestial highway around the sky called the ecliptic but at different rates depending upon their distance from the Sun. Distant Saturn and Neptune travel more slowly than closer-in planets like Mercury and Mars. Over time, we see them lap one another in the sky, pairing up for a week or so and inspiring the gaze of those lucky enough to look up. After these brief trysts, the worlds part ways and move on to future engagements.

Venus and Jupiter above St. Peter’s Dome in Rome on Sunday June 28, 2015. Details: Canon 7D Mark II DSLR, with a 17-55-f/2.8 lens at 24mm f/4 and exposure time was 1/40″. Credit: Gianluca Masi

In many conjunctions, the planets or the Moon and planet are relatively far apart. They may catch the eye but aren’t exactly jaw-dropping events. The most striking conjunctions involve close pairings of the brightest planets. Occasionally, the Moon joins the fray, intensifying the beauty of the scene even more.

As Venus orbits interior to Earth’s orbit, its apparent distance from the Sun (and phase) changes. Since June 6, the planet’s separation from the Sun in the sky has been shrinking and will reach a minimum on August 15, when the planet is directly between the Sun and Earth. Credit: Bob King

While moving planets are behind many conjunctions, they often don’t do it alone. Earth’s orbital motion around the Sun helps move things along. This week’s event is a perfect example. Venus is currently moving away from Jupiter in the sky but not quickly enough to avoid the encounter. Each night, its apparent distance from the Sun decreases by small increments and the planet loses altitude. Meanwhile, Jupiter’s moving away from Venus, traveling east toward Regulus as it orbits around the Sun.

So how can they possibly get together? Earth to the rescue! Every day, our planet travels some 1.6 million miles in our orbit, completing 584 million miles in one year. We see this movement reflected in the rising and setting times of the stars and planets.

View of Earth’s orbit seen from above the northern hemisphere. As our planet moves to the left or counterclockwise around the Sun, the background constellations appear to drift to the right or westward. This causes constellations and planets in the western sky to gradually drop lower every night, while those in the east rise higher. Credit: Bob King

Every night, the stars rise four minutes earlier than the night before. Over days and weeks, the minutes accumulate into hours. When stars rise earlier in the east, those in the west set earlier. In time, all stars and planets drift westward due to Earth’s revolution around the Sun.

It’s this seasonal drift that “pushes” Jupiter westward to eventually overtake a reluctant Venus. Despite appearances, in this particular conjunction, both planets are really fleeing one another!

Johannes Kepler’s depiction of the conjunction of Mercury (left), Jupiter and Saturn shortly before Christmas in the year 1603. He believed a similar conjunction or series of conjunctions – the Christmas Star – may have heralded the birth of Christ.

We’re attuned to unusual planetary groupings just as our ancestors were. While they might have seen a planetary alignment as a portent of kingly succession or ill fortune in battle, we’re free to appreciate them for their sheer beauty. Not to say that some might still read a message or experience a personal revelation at the sight. There’s something in us that sees special meaning in celestial alignments. We’re good at sensing change in our environment, so we sit up and take notice when unusual sky events occur like eclipses, bright comets and close pairings of the Moon and planets.

Venus and Jupiter over the next few nights facing west at dusk. Times and separations shown for central North America at 10 p.m. CDT. 30 minutes of arc or 30′ equals one Full Moon diameter. Source: Stellarium

You can watch the Jupiter-Venus conjunction several different ways. Naked eye of course is easiest. Just face west starting about an hour after sunset and drink it in. My mom, who’s almost 90, will be watching from her front step. Binoculars will add extra brilliance to the sight and perhaps show several moons of Jupiter.

The view through a small telescope of Jupiter (top) and Venus on June 30 around 9:30 p.m. CDT. Jupiter’s moons are G = Ganymede, E = Europa, I = Io and C = Callisto. Source: Stellarium

If you have a telescope, I encourage you to point it at the planetary doublet. Even a small scope will let you see Jupiter’s two dark, horizontal stripes — the North and South Equatorial Belts — and several moons. Venus will appear as a pure white, thick crescent 32 arc seconds across virtually identical in apparent size to Jupiter. To tame Venus’ glare, start observing early when the sky is still flush with pale blue twilight. I think the best part will be seeing both planets in the same field of view even at moderate magnification — a rare sight!

To capture an image of these shiny baubles try using your cellphone. For many, that’s the only camera we have. First, find a pretty scene to frame the pair. Hold your phone rock-solid steady against a post or building and click away starting about an hour after sundown when the two planets have good contrast with the sky, but with light still about. If your pictures appear too dark or light, manually adjust the exposure. Here’s a youtube video on how to do it with an iPhone.

Jupiter and Venus at dusk on June 26. This is a 6-second exposure at f/2.8 and ISO 80 taken with a basic point-and-shoot digital camera. I braced the camera on top of a mailbox and stuck my phone underneath to prop up the lens. Credit: Bob King

Point-and-shoot camera owners should place their camera on a tripod, adjust the ISO or sensitivity to 100, open the aperture or f/stop to its widest setting (f/2.8 or f/4), autofocus on the planets and expose from 5-10 seconds in mid-twilight or about 1 hour to 90 minutes after sunset. The low ISO is necessary to keep the images from turning grainy. High-end digital SLR cameras have no such limitations and can be used at ISO 1600 or higher. As always, review the back screen to make sure you’re exposing properly.

I’m not a harmonic convergence kind of guy, but I believe this week’s grand conjunction, visible from so many places on Earth, will stir a few souls and help us appreciate this life that much more.

Bob King

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.

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