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Comment by gumby | Hacker News Reader

Couldn't a zodiac be dated through the configuration of the stars?

Probably not. It's not really a star chart and astrologers tend to not update their zodiac as precession causes drift over time.

https://earthsky.org/astronomy-essentials/what-is-the-zodiac...

That’s a good link. Sidereal time is interesting. Like a Mercury day is longer than it’s year. Wild

This intrigued me, so I looked it up. Sadly, your memory doesn’t seem to be correct. Mercury’s day is 59 earth days and its year is 88 earth days.

https://www.nhm.ac.uk/discover/planet-mercury.html

It depends on the definition of a “day” that you use, but due to Mercury’s elliptical orbit sunrises and sunsets are weird. [1] It takes 59 Earth days for the planet to revolve once around its axis, but from the surface it takes 176 Earth days to observe the sun making a complete circuit of the sky.

https://solarsystem.nasa.gov/planets/mercury/in-depth.amp

This is the weirdest thing at that link:

> But when Mercury is moving fastest in its elliptical orbit around the Sun (and it is closest to the Sun), each rotation is not accompanied by sunrise and sunset like it is on most other planets. The morning Sun appears to rise briefly, set, and rise again from some parts of the planet's surface.

There are two different definitions of "day". The sidereal day is the time it takes for a body to complete a full 360° rotation about its axis. The synodic day is the time between success zenith passings of the parent body. If the body rotates in the same direction as its orbits, the synodic day is longer than the sidereal day; if its rotation is in the opposite direction, the sidereal day is longer.

On Earth, the synodic day is 24 hours long, and the sidereal day is about 4 minutes shorter. In the case of Mercury, the sidereal day is 59 Earth days and the synodic day is 176 Earth days. Note that the synodic day is the one we on Earth use to define the length of a day for timekeeping purposes--it's a lot easier to measure synodic time than sidereal time.

Your wikipedia link indicates that the current dating of the Dendera zodiac is based on the configuration of the planets within it.

I didn't read it. I was interested in a better image.

Though planets used to be called wandering stars, stars and planets are not the same thing. If this piece actually contains a planetary configuration, that's a fairly reliable means to identify a timeframe, yes.

At least one article about exactly that process has appeared on HN before.

https://news.ycombinator.com/item?id=33943509

Zodiac is the wheel of signs based on constellations and the word is not synonymous with "astrological chart."

Reply on news.ycombinator.com