You may have spotted Venus low in the northwestern sky at dusk. But I bet you haven't seen Mars in weeks. There's a reason for that. The planet is currently moving to the far side of the sun nearly opposite the Earth. With 231 million miles (372 million km) between us, Mars is almost seven times more distant and 100 times fainter than when it's closest to Earth.
Venus shines about 250 times brighter than the Red Planet with a magnitude of -3.9 vs. 1.8 for Mars. Normally, a second magnitude planet would be easily visible in a dark sky. Therein lies the problem. Mars is only visible at dusk right now and very low in the sky to boot. This makes it appear usually faint. So why bother looking at all?
Because it's on a collision course with Venus! Not a real smashup, of course, but the line-of-sight kind we call a conjunction. On July 7, they were 3.2° apart, equal to about six full-moon diameters. The two are drawing closer every day as Mars creeps closer to the western horizon, and Venus slides eastward to meet it.
On Thursday evening (July 8), they'll be 2.6° apart and squeeze closest together on Monday, July 12, separated by just 0.5° or one moon diameter. Unfortunately, Mars is too faint to see with the unaided eye for the reasons described above, so you'll need to watch it happen through binoculars. My 8x40 and 10x50 pairs show Mars with ease. It's amazing how much fainter it is than Venus — a spark compared to a bonfire.
On Sunday, July 11, the day before the conjunction, a stunning 2-day-old moon will add a touch of its own magic to the celestial scene, appearing about 5° to the right of the planet-pair. All three objects will lie along a line approximately level with the western horizon. Be sure to bring a camera. And don't forget those binoculars!
To see it all happen, you'll need a clear, unobstructed view as far down to the west-northwest horizon as possible. The planets will appear about two fists to the left of the sun's setting point. Venus should be obvious starting about 45 minutes after sunset and remain visible for about a half-hour. Find your local sunset time here.
When you spot Venus, aim your binoculars at the planet and focus it to a point, then look for fainter Mars to its left. You can start watching the very next clear night. The sooner you begin, the greater the pleasure of anticipating their July 12 embrace.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.