Venus Speed-dates Mercury En Route To Transit

Venus and Mercury approach each other earlier this morning as seen in this photo taken by the Solar and Heliospheric Observatory (SOHO) coronagraph. The sun is blocked by the blue disk so we can see its corona. Credit: NASA/ESA

As if we haven’t had enough excitement with the recent partial solar eclipse and coming transit of Venus and partial eclipse of the moon, you can now add one more event to your calendar – a conjunction of Venus and Mercury. That happens today at 3 p.m. Central time when the sun is high in the sky over the U.S. The two planets will be only 1/5 of a degree apart at the time. Very close!

Venus and Mercury are two peas in a pod today. Telescopes users who take special precautions to avoid the sun can see them both in daylight. They'll also be visible very low in the west in binoculars right after sunset. Created with Stellarium

Amateur astronomers who have the ability to precisely point their telescopes at a particular spot in the sky day or night can attempt to see the planetary pair in broad daylight. Once Venus is found, Mercury will be in the same field of view just north of the much brighter planet.

Take great care to avoid the sun, which will be only 6 degrees to the west. If you succeed, you’ll also witness one of the thinnest Venus crescents ever. A mere 0.7 % of the planet will be illuminated by the sun at the time. A word of caution: Do not attempt to find this with binoculars or you may accidentally point them at the sun and damage your eyes.

Through a scope, Venus will look wire-thin today. If the air is especially clear and your scope has good optics, you might be able to trace the crescent around the entire disk of the planet. It's visible from sunlight backlighting the planet's atmosphere - a rare sight! Created with Chris Mariott's SkyMap software

European observers are more fortunate. The conjunction happens around the time of sunset with the sun safely out of the picture. A wide-open horizon to the northwest, haze-free skies and a pair of binoculars will show brighter Venus, and next to it, the planet Mercury, shining at magnitude -1.6. That’s as brilliant as Sirius, the brightest star, but being so near the sun, the planet will appear much fainter.

U.S. observers can also watch the pair shortly after sunset; they’ll still be close together though not as tight as during the afternoon. Venus’ big crescent should be plain in almost any pair of binoculars.

Cruddy photo of Venus and Mercury (top) this morning June 1 through a 4-inch scope. Photo: Bob King

I found slender goddess and star-like Mercury with my 4-inch refractor earlier this morning by using a solar filter to center the sun and then offsetting from it the appropriate distance. Venus was amazing as you might imagine, with Mercury easily visible to the west in the same field of view.

Although the two planets look like they might bump into each other, Venus is in the foreground in front of the sun 27.3 million miles from Earth, while Mercury’s in the background on the opposite side of the sun 120.5 million miles away. Their different locations in relation to sun and Earth also mean their phases aren’t the same: Venus is a crescent, Mercury looks like a tiny full moon through a telescope.

Transits would be much more common if it weren't for Venus' orbit, which is tilted 3.4 degrees relative to Earth's. The tilt is exaggerated here for clarity. Illustration: Bob King

With each passing day, Venus gets closer and closer to transit time. We’re all excited about the event as we anticipate the rare and curious sight of a planet silhouetted against sun. The last pair of transits happened in 1874 and 1882, and most of us won’t be around for the next pair in 2117 and 2125. If Venus’ orbit were exactly in the same plane as Earth’s, we’d have a transit every 8 years when the planet passed through inferior conjunction. That’s when the two planets lie on a line on the same side of the sun.

Instead, the planet’s tilted orbit guarantees that most of the time Venus misses the sun when we line up, passing a little north (above) or south (below) it. How nice to finally hit the nail on the head next Tuesday.

8 Responses

  1. john

    Bob, I’m heading up to the northshore next week… any possiblity of solar activity and northern lights???

    1. astrobob

      Hi John,
      While there have been a fair number of sunspot groups lately, most have been smaller and quiet. Nothing in the forecast I can see next week. Good news is that the moon will soon be out of the evening sky.

  2. caralex

    Bob, I’ve never been able to find an explanation of the timing of the transits. Can you explain, maybe with a diagram, how a very short interval, just 8 years, is followed by such a long one, either 105 years or 121 years, on a regular basis. I’ve never found a website that spells it out precisely! Thanks!

    1. astrobob

      Hi Carol,
      It is a bit complicated. In a very general way, we get two in a row because Venus and Earth are in the same flat plane for two inferior conjunctions of Venus in a row or about 16 years. Before that, Venus is too far south of the Earth’s plane, and after that, Venus strays too far north. Here’s a much more thorough explanation that I hope will help: http://www.rasnz.org.nz/2012Transit/Transits.html

  3. Pallavi

    Hi, need your expert advice we r at ely, mn and the kp index is 3 now, do you think I should camp out to see the northern lights? The horizon is pinkish.. It could be my optimism .. Any advice will help thanks!!!!

    1. astrobob

      Hi Pallavi,
      Nothing out for N. Minn. yet. Any aurora is still further north in Canada. The Kp is up a little, at level 3 of of 10 p.m. Stronger activity is now expected for tomorrow night and Monday. It’s clear in Duluth also, so I’ll be on the lookout, but with a bright moon, I don’t expect to see much unless there’s a big spike.

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