You could only determine the time period from stellar observation of stars in nearby neighborhood a few million years at most with increasing uncertainty out past a few hundred thousand years. A potentially better estimate over longer periods would be of the Magellenic clouds (actually dwaft galaxies) which orbit the Milky Way, but there is significant disagreement over their orbital parameters, or indeed, if they are actually in a regular closed orbit at all. Trying to determine the period from relative positions of the planets alone beyond a few tends of thousands years is not really workable; there are too many essentially identical permutations, and we’ve come to understand that the orbits of planets may be more perturbative than we previously expected.
The best way to estimate the time period over a very long period is not to look outward but rather inward, looking at the ratios of long half-life isotopes. Clair Patterson accurately estimated the age of the Earth as 4.55 Bya +/-70 Mya or within about +/-1.5% of the age of the Earth. (As an aside, he also discovered the hazards of environmental comtamination from the use of tetraethyl lead in gasoline and spent more than three decades campaigning for its removal.). You could also make rough estimates by looking at the temperature of the cosmic microwave background and or the redshift Cepheid variables, but these aren’t going to be very precise, on the order of hundreds of millions of years.
Darren Garrison, if I’m not mistaken, that would just tell you when the meteoroid formed, but not anything about how long it was floating around in space before you found it.
Stranger, can you show your work for “hundreds of millions of years” for the CMB? The temperature of the Universe is roughly inversely proportional to its age, and we can currently measure the temperature to about 1 part in 10^4, so we should be able to get time to about 1 part in 10^4 of the Universe’s entire age, or about a million years.
When you do an isochron on a primitive meteorite today you get an age around 4.55 billion years. If you test a primitive meteorite and find that it is 4.48 billion years old, you will know that you are in the Cretaceous. (If you get an age of 4.00 billion years and you are dying of hypoxia in a barren wasteland, you will know that you are in the Cambrian.)
Years[sup]6[/sup] for all six planets … [sigh] … still, measuring CBR is an elegant solution, and not confined to post-Cambrian time frames … that’s like knowing which county you’re in …
For larger timescales, how about solar spectroscopy? I don’t know how precisely we can measure the components of the sun, but there will be more hydrogen earlier, more helium later.
As I understand it, most of the helium produced by the sun stays buried in the core, so it doesn’t show up in the spectrum. The stuff that does show up in the spectrum (which is how helium was first discovered) is residual from the solar nebula, which got most of it from the Big Bang.
Hmm. Further reading indicates that you are probably right: this article says that the way we figure out how old stars are is by looking at nearby stars that are in the later stages, and going by mass. So, no good on that one.