View Full Version : Seeing in the Dark

2003-Feb-25, 02:43 PM
I'm half way through the book Seeing in the Dark, by Timothy Ferris. Excellent book, as Chip has mentioned before, I highly recommend it. Even on topics about which I've read a dozen articles, I've found new and interesting details in Ferris's book.

I do have a nit (of course!). On page 90, he discusses the Calendar Rounds of the Mayans, which repeats every 52 years, and says that "Venus appears in the same spot in the sky, on the same date, that it did 52 years earlier."

He goes on to discuss the orbital periods of Venus and the Earth and the early Mayan observatories, but...that statement is wrong. The Calendar Round is 52 years because the Mayans used two different calendars, one of 13 20-day periods and another of 12 30-day months plus five days, and 73 copies of the first exactly equaled 52 copies of the second. Although each may have been based upon the Venus and Earth orbital periods, neither closely matches the actual orbital period of Venus (224.701 days) or Earth (365.256 days), and Venus does not return to the same spot on the same date after 52 years, whether you use our calendar or one of the Mayan's calendars.

Actually, the ratio of the Earth/Venus periods is 1.6255, very close to 13/8, so that after 8 of our years, Venus is just a tad past where it was 8 years before, having just completed 13 (13.004) of its own revolutions about the Sun. 52 is not divisible by 8--in fact, after 52 of our years, Venus is about as far away from where it started as it can get.

At least, according to my calculations, which haven't gone too well as of late... /phpBB/images/smiles/icon_smile.gif

2003-Feb-26, 12:54 AM
I agree with your math. If Venus does 1.6255 revolutions for 1.0 Earth revolution, then in 8 Earth years, Venus has done 13 revolutions and should be in the same place in the sky.

Since 4 times 13 is 52, I wonder if Mr. Ferris got his math backwards. Lord knows, I do quite often.

2003-Feb-26, 05:11 AM
No, he was using the Calendar Round of the Mayans--52 years.

Most of the rest of the book is very good.