Assumption Day

For Venus, this year falls into two acts, and August 15 is the date that divides them.

Imagine a performer, a “star”, who for the first seven months has been exhibiting herself on the stage in the west, that is, the stage of the sunset horizon. Then she slips out of view, as if ducking down from the stage, and reappears to perform for the rest of the year on an opposite stage, in the east, around the dawn of each day.

The slipping from stage to stage actually consists of sprinting by in front of the Sun: a maneuver called Venus’s “inferior conjunction.”

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For a few days, Venus is not really out of view, but is too close to the Sun’s glare to be detectable.

Venus’s orbit is not quite in the same plane as Earth’s (the ecliptic) but tilted to it at about 3 degrees. The result is that at these inferior conjunctions, which happen about every 19 months. Venus sometimes passes north of the Sun, sometimes south of it, rarely right in front of it (a transit, as in 2012).

In the famous eight-year Venus cycle (recognized by the sky-watchers of several ancient civilizations), years of the 2007-and-2015-and-2023 type are years when Venus at its inferior conjunction passes south of the Sun, by as wide a clearance as it can – about 8 degrees. (This is, very roughly, the span covered by your fingers and thumb held together at arm’s length.)

The result of this is that, for observers in northern latitudes such as the US and Europe, Venus disappears from sight for quite a long time. It gets so low in the sunset sky that by August 1 it is only 5 degrees higher than the Sun, and on August 8 sets with the Sun, so that over the next couple of weeks it is underground at sunset. It won’t be seen again till the mornings of about August 23 onward.

Here are adapted parts of the pictures from the “Mercury and Venus horizon scenes” section of Astronomical Calendar 2015. First, at left, you see Venus getting lower in the western sky. (Its size is magnified 480 times to show, as in a telescope, its long thin crescent shape as it moves between us and the Sun; its real size is more like one of the dots.  The Sun is at true scale.) Venus dips below the horizon and passes south of the Sun on Aug. 15. Then it emerges into the right-hand picture – that is, into the pre-dawn eastern sky.

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But for people in the southern hemisphere, for whom south is up, Venus passes that much above the Sun. Here is how the same motions appear, very differently, for a South African or New Zealander. On the right is Venus’s progress down the evening sky. On August 15, being 8 degrees south of the Sun means being that much above it. Venus never disappears, because already on the morning of that day, or even a day or two earlier, it is findable with skilfullu used binoculars or telescope above the part of the horizon where the Sun will soon rise.

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That is the feat of seeing Venus at or very near inferior conjunction, even in both the morning and evening of the same day. There is something as magical about it as the feat of seeing the New Moon at an eclipse. You catch the performer during her secret tunneling from stage to stage.

And, you may ask, is there a kind of year in the Venus Cycle when we northerners get to see Venus passing widely above the Sun? Yes: 2001, 2009, and 2017, each time in March. Venus even clears the Sun by a slightly larger angle than it vouchsafes for southerners.

August 15 is also a birthday, but the lady who told me not to mention this suggested mentioning instead that it is Assumption Day. Yes, it is the Feast of the Assumption of the Virgin Mary into Heaven. We could say that it marks her (or Venus’s) passing from a plainly visible life in one world to a less obvious life in another. On looking this up, I found that the day is “contemporarily” to be called not the Feast but the Solemnity of the Assumption. “Feast,” it seems, is too frivolous for the Holy Days in the calendar.

Good King Wenceslas looked out
On the solemnity of Steven…

 

 

3 thoughts on “Assumption Day”

  1. I saw Venus this morning for the first time during her current morning apparition. I walked up a nearby hill before dawn to get a clear view to the east over San Francisco Bay. Venus was a brilliant light well above the cloudy horizon 45 minutes before sunrise, and a beautiful crescent through mounted 11×56 binoculars. After spending so much time with her when she was an evening planet, it felt a bit strange that the view got better over time (rather than worse), as she rose higher and the sky brightened. I enjoyed showing Venus to a few early morning dog walkers, and three young Polish tourists who were in San Francisco for the first time — they had walked up the hill to watch the Sun rise. It was fun to point out the prominent landmarks, and to commiserate about our respective reactionary demagogue politicians.

  2. Thanks Guy. 2017 will be an interesting year for seeing our sister planets passing in front of the Sun: Venus with a wide inferior conjunction in March, and the Moon eclipsing the Sun in August.

  3. I think the lady doth protest too much. Maybe that’s why I had to click on the spot to view this episode of your ever so dear blog, especially for something as exciting as an inferiour conjunction of venus. I consider myself extremely blessed by seeing both transits, the 2004 one from Switzerland, with my friend whom I met during the grand 7/11/91 eclipse of the sun in Baja, CA, and the 2114 on in Maui with a college buddy of mine who happened to be living in Shanghai when I took a tour for another eclipse of the sun in July 2009. Happy Birthday!

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