If I time travel back to a random location...

[RadicalPi]

@Chronos

Precession could get you to within, say, a few hundred years, modulo the 33,000 year cycle (the easiest way to do this would be to see what star is closest to the rotational pole-- It isn’t always alpha Ursa Minoris). Then, you’d use observations of the various planets to find a time consistent with your precession measurement when all the planets are in the right locations: With low-precision equipment, this could get you to within a month or less. Finally, then, you use the phase of the moon to narrow that month down to a day. As a check, you can use observations of the directions of sunrise and sunset to tell you the time of year.

Incidentally, this seems like it would make a good challenge question for someone like myself (good at math, bad at science). Give me some star charts and whatnot for some random day 8,000 years ago and see if I can determine the exact date.

[brocks]

@RadicalPi

At least, this is how I understood the method.

Right, don’t know what I was thinking.

So, given all that, it looks like the biggest problem is determining which 33000-year precessional cycle you’re in.

Could we use the proper motion of familiar stars to figure out what the constellations would look like at various times in the past, and be able to correctly determine times much farther back than 33000 years?

[Uncertain]

@Superhal

a. a carbon dating machine that runs on nuclear power

How will that help?

[RadicalPi]

@brocks

Right, don’t know what I was thinking.

So, given all that, it looks like the biggest problem is determining which 33000-year precessional cycle you’re in.

Could we use the proper motion of familiar stars to figure out what the constellations would look like at various times in the past, and be able to correctly determine times much farther back than 33000 years?

I was just wondering about that myself. The question here is, I think, how much do the stars move over 33,000 years. Random searching online says that the average proper motion of naked-eye stars is about a second of arc every ten years, which means that over 33,000 years you get about a degree. I honestly don’t know if that’s enough or not.

[Chronos]

Stars being out of position by a degree or so (and keep in mind that they’ll all be out of position in completely different directions) would be enough to visibly distort the constellations, but I don’t know if you could get anything precise enough to be all that useful, by the naked eye. That would be a good indicator, though, for “I’m way the Hell far back”.

And carbon dating won’t tell you much of anything interesting, but if you’re in the past few tens of thousands of years, a dendrochronology record could help, and if you can find any uranium ore, you could do radioisotope dating on that to get a broad-scale picture (to within hundreds or maybe tens of millions of years).

[Ludovic]

@Uncertain

How will that help?

Indeed, that would only help if you knew where you were and some convenient ruins were nearby. Then you’d have to excavate them and determine how old they were and use your knowledge of how old they should be to determine what year it is.