When plotted geocentrically – from an Earth-centered perspective – there is a highly noticeable rhythm in the motion of Venus. After 8 years, it returns to the same place in the sky on the same date. This was known to, and of great interest to, ancient peoples such as the Maya, and many today know it as the famous Venus cycle, or the pentagram of Venus.
Over eight years, each phenomenon – each relative position of Earth, Venus, and the sun – occurs five times, and then over the next eight years they repeat five times almost identically.
For Venus, the tight inward loops are the inferior conjunctions, in which Venus passes between us and the sun; the wide swings are centered on the superior conjunctions, when Venus passes around the far side of the sun. So the general pattern is (as Anthony Barreiro commented):
… a lovely five-petalled rose.
The tight loops are the stamens of the rose, the wide swings are the petals.
When I tried to plot a geocentric picture over eight years (2016-2023) to show the complete rose, it was bewilderingly cluttered. It had five overlapping tracks, eight-times-twelve little Venus globes at monthly intervals – already too much without the ecliptic-plane grid and other details.
The image at the top of this post is a more simplified version: still calculated in three dimensions, but, by moving the viewpoint to the north ecliptic pole, it becomes a flat plan of Venus’s path.
Earth is in the middle; the vernal-equinox direction is to the right; the yellow spots are the sun at the beginning of each month.
The rest is the rhythmic motions of Venus.
You’ll still have trouble deciphering which part of the track is for which year (I’ve used white, cyan, magenta, yellow for 2016, 2017, 2018, 2019, and again for 2020, 2021, 2022, 2023) but it doesn’t matter greatly. You can see the five inferior conjunctions, in their five directions.
If you trace across the circle from each loop to the next, you see that they are not adjacent to each other but 2/5 pf the way around, like the five points of a pentagram.
The directions of the five inferior conjunctions determine their differing characters, by determining their places in Venus’s “true” (heliocentric) orbit, which is tilted and slightly elliptical.
2017 Mar 25: in Pisces; Venus passes 8 degrees north of the sun; distance from us 0.28 AU (astronomical units, sun-Earth distance); diameter of Venus’s (mostly dark) disk 60? (arc seconds).
2018 Oct 26: in Virgo; 6° degree south of the sun; 0.27 AU; 62?.
2020 Jun 3: in Taurus; 0.5° north of the sun; 0.29 AU; 58?.
2022 Jan 9: in Sagittarius; 5° north of the sun; 0.27 AU; 63?.
2023 Aug 13: Cancer-Leo-Hydra border; 7° degrees south of the sun; 0.29 AU; 58?.
March 2017 is the next of those wonderful occasions, like March 2009, when we in the Northern Hemisphere have a chance to see Venus pass so far north of the sun that it may be visible near to both sunset and sunrise of the days near, and even the day of, inferior conjunction.
And years of the 2023 type are the similar opportunities for Southern Hemisphere dwellers.
Having brought Venus into conjunction with petals and the southern hemisphere, I may be forgiven for remembering the limerick that rhymes in éili@.
There was a young gal from Australia
Who went to a ball as a dahlia.
When the petals unfurled
It was known to the world
That the dress – as a dress – was a failure.
Article written and published originally by Guy Ottewell at his blog.
Bottom line: The highly noticeable rhythm in the motion of Venus from an geocentric perspective is famously mentioned in The Da Vinci Code by Dan Brown, and sometimes called the pentagram of Venus. Guy Ottewell provides a beautiful chart and explains more, here.
Astronomer, artist and poet Guy Ottewell's beloved Astronomical Calendar is now in its 43rd and final year. Visit Guy’s website UniversalWorkshop.com or his blog at UniversalWorkshop.com/Guysblog. His stories and art are used here with permission. Thank you, Guy!