Abri Blanchard Calendar: Yíngshì Two

If we look at the position of Yíngshì above the horizon, we might better understand how it could be used to mark the start of a new era.

Image: Your Sky
Image: Your Sky

The Abri Blanchard faces west. In the view of the horizon (left), as at UTC 16:43 on 2 February 2013, just before sunset, you can see the sun setting. The sun’s position is at 315° longitude on the ecliptic. Higher up, you can see the constellation Yíngshì, which is currently positioned between longitudes 0°; the vernal equinox, and around 352.5°. Yíngshì takes up about 7.5° of the sky when measured along the ecliptic.

Yíngshì precesses (appears to move) along the ecliptic at the rate of one degree every 71.566 years. The sun, moon and planets appear to move at rates determined by their individual orbits.

Image: Your Sky: Additional Annotation: Lynn Fawcett
Image: Your Sky: Additional Annotation: Lynn Fawcett

If we take what Liú Xiàng said literally, we can create an imaginary view of the horizon that marks the start of a new era. To illustrate, I have taken the start of spring to be the 2 February. On this date, Yíngshì would have been in the correct position in 1201 BCE. On the left, is a simulated view of the horizon at UTC 16:43 on 2 February 1201 BCE, which shows Yíngshì just above the 315° longitude mark. I have added the Sun and the New Moon coming in to set followed by the five planets.

If we decided to use the vernal equinox to mark the beginning of spring, Yíngshì would be located at 0° longitude on the ecliptic. It is possible to create a similar imaginary scenario there, but in a different calendar year.

Regardless of where we place Yíngshì, precession means that there is a very small window of opportunity within each 25,764 year cycle in which such a conjunction could occur. The likelihood therefore of a conjunction of the Sun, the Moon and the five planets at the start of spring in an area of the sky marked by the constellation of Yíngshì is very tiny indeed.

In deciding on Yíngshì’s contribution to the almanac, I think that it is necessary to apply a little common sense. Something that is highly unlikely to occur, even within a cycle of 25,764 years, is not going to be the subject of a pocket almanac. I therefore think that perhaps Liú Xiàng was referring to the layout of a calendar or almanac, and not to the remote possibility of a conjunction with Yíngshì as the backdrop.

Reference

Image Credits:

View of the horizon for an observer at the Abri Blanchard on 2 February 2013: Your Sky by John Walker: http://www.fourmilab.ch/yoursky/: Accessed: July 2013

View of the horizon for an observer at the Abri Blanchard based on a sky map for 2 February 1201 BCE: Your Sky by John Walker: Simulated conjunction of the Sun, the Moon and the five planets by Lynn Fawcett: http://www.fourmilab.ch/yoursky/: Accessed: July 2013