March 25, 2017

Venus: A Pre-Transit Spring Showcase.

Venus in 2003. (Photo by Author)

The planet Venus is putting on quite a show for the spring of 2012, fresh off of its close conjunction with Jupiter on March 13th and enroute as to a starring role in the astronomical event of the year, its final transit in front of the Sun for this century on June 5th-6th. As the brightest and nearest planet to our own is now prominently placed high in the dusk sky for northern hemisphere viewers, we thought we’d take this week to look at all things Cytherean coming up this spring and insider’s guide of what to watch out for;

The passage of the crescent Moon past Jupiter & Venus March 25th-26th,

(Created by the Author in Starry Night).

First up on the night of March 25th and 26th, the 3-day old crescent Moon completes a nice grouping with Jupiter and Venus in the dusk skies. Now is a great time to try your hand at daytime Venus-spotting and amaze (or disturb) your neighbors with feats of visual prowess. Close passes also occur later this spring on the nights of April 25th and May 22nd.

Jupiter & Venus Attack! The close conjunction of March 13th. (Photo by Author).

On March 27th, Venus reaches greatest eastern elongation, just six days after perihelion. Venus is a maximum of 46° degrees east of the Sun high to the west. This is the most northern elongation of this entire eight year cycle.

On March 29th, Venus reaches a point of theoretical dichotomy or half phase as viewed from Earth. A strange factoid about dichotomy is that it often appears to occur up to 10 days prior to the predicted date; is this a result of atmospheric refraction along the terminator, or an illusion stemming from starring at a dazzling, featureless globe? On what date does Venus appear like a half moon through a telescope to you?

The Passage of Venus by the Pleiades in early April. (Created by the Author in Starry Night).

On April 2nd-5th, Venus passes the Pleiades open star cluster, a great photo-op! This pairing is the latest in a set that is occurring on an 8-year cycle, first occurring in April 2004 and next occurring in April 2020. Venus won’t, however, begin passing between any bright stars in the Pleiades until 2028!

On April 30th, Venus reaches a greatest brilliancy of magnitude -4.5 and displays its maximum illuminated area for this apparition. Can you see or photograph a shadow cast by its light? The next week or so is a good time to try!

On May 1st, Venus reaches greater than 40” in size and is a noticeable crescent in a small telescope. An elusive phenomenon to watch for around crescent phase is known as the “Ashen light of Venus” on its nighttime side, a ghostly glow similar to that seen on the crescent Moon. How can this be, you ask, since Venus has no moon? Various explanations have cropped up over the years, from aurorae to lightning to airglow. Other suggestions are a simple optical illusion (we expect to see a faint night side, which our brain promptly fills in) but the observation has been an enduring one over the years. A current contender is the near-Infrared glow of the dissipating heat from the surface diffusing though the clouds. At 860° Fahrenheit, it is really hot down there! The advent of amateurs actually catching detail on Venus via ultraviolet and infrared photography may go a long ways towards solving this mystery.  Venus will continue to grow in visual size until it reaches 58” arc seconds in diameter during the June transit. This is the largest that any planet can appear from the Earth. And this also begs the question; can anyone observe the crescent with the naked eye? There are many reports of successfully spotting the tiny crescent Venus, but of course, like many things Venusian, it is easy for the mind to fool us. Attempting this sighting when Venus is high in the sky during the daytime or using a polarizing filter may help… but no magnification; that’s cheating! Personally, I would be convinced if someone could correctly note the orientation of the crescent that had no astronomical knowledge of which way it should be oriented. It is also interesting to note that few reliable pre-telescopic mentions of a crescent Venus exists prior to Galileo’s first observations of the planet in 1610.

The changing phases of Venus leading up to the last transit in 2004.

(Credit: ESO-Southern Observatory: Statis Kalyvas – VT-2004 programme).

On May 4th, Venus reaches its most northern declination for the remainder of the century, at just over +27° degrees and 49’ arc minutes north. In fact, it will not surpass this feat until May 7th, 2239 A.D.! This means that from latitude +63° degrees northward (Anchorage, Alaska is just below +62°) Venus will become “circumpolar!” Even from middle northern latitudes, Venus won’t set until past 11 PM local.

On May 20th, an annular solar eclipse will cross the Pacific Rim from Japan to the U.S. West Coast. An interesting phenomena to watch out for during annularity will be the appearance of a -4.3 magnitude Venus about 24° degrees east of the 94.4% eclipsed Sun… can you spot it in the “counterfeit twilight?”

On June 1st, Venus will pass only 0.26° degrees SSW of Mercury, in the closest planet-planet conjunction of the year. This all occurs, however, only seven degrees east of the Sun low in the dusk, just a scant four days before the big ticket event of 2012;

The June 5th-6th: transit! We’ll have a special dedicated post on this unique event, how to see it, and other factoids of transit bizarre-ness that you’ll only find here, as we follow one of the greatest floor-shows in the solar system!



  1. [...] 3rd: Venus is near the Pleiades at sunset, on a cycle of transits in front of the open cluster occurring every 8 years until [...]

  2. [...] of the best the sky has to offer. But as the Moon remains at slender crescent phase this week and Venus makes its dive sunward for its last transit of the 21st century, we thought we’d take a look at two [...]

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