With all the rainy weather we’ve had here lately stargazing has not only been difficult but also pretty low on the priority list for many of us. But if you’ve taken advantage of those infrequent occasions when the clouds have been few and you’ve looked off to the west right after sunset you may have noticed the light show that is Venus and Jupiter both burning brightly in the night. They are the brightest objects in this part of the sky right now and are about 20 degrees apart (two fist widths held out at arms length). They make a lovely pair don’t they? Well, hang on because, as the saying goes, you ain’t seen nothing yet.
As the month goes by you will see the two planets get closer and closer together in our early evening sky and by the end of June, and into the early part of July, Jupiter and Venus will appear so close that you will need a telescope to separate them apart. These close alignments of two or more planets in the sky are known as a “conjunction” and they are great spectacles to observe.
Think of the planets orbiting around the Sun as cars in a NASCAR race. The glowing ball of plasma we call the Sun sits in the center and the planets all occupy their own individual tracks as they orbit around it. They all travel at different speeds depending on their respective orbital positions. Mercury, the innermost planet, zips around the Sun in just 88 of our days while Venus takes 225 Earth days. Meanwhile, the gas giant planets are much more leisurely in their travels. Jupiter takes 12 of our years to complete one lap around the Sun while Saturn takes 29 years. Pluto, one of the most distant worlds in our solar system, takes a whopping 250 Earth years to complete one trip! Now, imagine you are out in space hovering “above” the solar system and watching this planetary NASCAR race. You will soon see that the speedy inner planets often overtake the giant, outer slow poke planets, align briefly with them, and then pass them by. This is what you are seeing when you watch Venus and Jupiter this month. No special equipment needed. With just your unaided eye you can bear witness to the awesome power of gravity and planetary motion in action.
All objects with mass exert a gravitational influence upon other objects with mass and the more mass an object has the stronger its gravitational pull. The Sun is the most massive object in our solar system so it rules the roost when it comes to gravity and all of the planets dance to its tune. The planets move in elliptically shaped orbits as they revolve around the Sun (rather than flying off in a straight line) because the Sun’s mass warps the fabric of space around it. This is, in a nutshell, Einstein’s concept of General Relativity where gravity is a property of space-time geometry rather than an ordinary force. Also, the planets don’t fall into the Sun or fly off into space because they maintain a constant velocity that keeps them within their respective orbits around our star. And, the planets all orbit the Sun in roughly the same plane. But why?
Well, the planets formed out of a flattened, rotating disc of gas and dust leftover from the Sun’s formation some 5 billion years ago. As a result, all of the planets occupy the same plane as they move around the Sun. We too are embedded within this plane and we see it edge on in our sky. We call the path through which the Sun, Moon, and planets all move across the sky the “ecliptic” and it is in fact nothing more than the plane of our solar system viewed edge on. This is why we can see planets like Venus and Jupiter come together in a conjunction like this. It’s all purely a line of sight effect, Venus and Jupiter are not really this close, they just look like it from our Earth-bound point of view. In fact, on June 30th, when they appear closest together in the sky all month, Venus is 47 million miles away and approaching Earth on our side of the Sun. Meanwhile, Jupiter is on the opposite side of the Sun and is some 559 million miles away.
Be sure and check up on these two planets on the night of June 19th because the crescent Moon gets in on the act as well and is only a few degrees below Venus on this evening.
After the pair has their apparent rendezvous at the end of the month watch them separate and go their merry way during early July.
Don’t be too surprised if you hear astrologers or doomsday prophesiers making a big deal out this alignment. Astrologers may tell you that this conjunction will hold special significance for your love life while doomsday pundits may claim the alignment will cause earthquakes, tidal waves, or the break up of Kim Kardashian and Kanye West. It’s all nonsense of course and to them I quote the famous catchphrase of my favorite fictional armchair detective, Nero Wolfe: “Phooey!” Also, when Venus and Jupiter are at their closest (and cannot be separated with the unaided eye) their combined brightness may even spark a few UFO reports.
While those folks are wringing their hands in the dark the rest of us will be outside with our eyes firmly fixed to the western sky and simply enjoying one of Nature’s grand spectacles.
Darrell Heath works at the University of Arkansas at Little Rock and is a producer and host for the UALR Television show “The Night Sky.”