Keith,

This is generally a non-issue.

Certainly, a galaxy is sufficiently large that two opposing points on it may be separated by a few hundred thousand light years. Thus, when we look at that galaxy, we're seeing parts of it at different times than other regions.

But galaxies are, in general, many millions of light years distant, and so the 'scatter' arising from the size of the object is generally lost in the noise/uncertainty that arises from all cosmic observations.

Thanks Charles and James,

As an archaeologist researching spatio-temporal relationships from a very 'down-to-earth' perspective I'm struggling to put my question in a way that best embodies my understanding (or astronomical lack of astrophysics domain knowledge :-) ) on this. But here goes...

"It depends how far away the object is" does that mean far away in Time or Space? (Or both together if that's what you mean?)

In Archaeology we try to identify, distinguish, and sequence different physical entities and associated events in time with differing chronological resolution (Lucas) e.g. approximating the date for the construction of a building. We have a few methodologies for doing so. One well known one is radio-carbon dating. Another is derived from the study of geological stratigraphy and based upon the Law of Superposition (Nicholas Steno, and James Lyell) which has been adapted for archaeological (human generated) stratigraphy (Harris 1979), where the juxtaposition of different physical layers is 'interpreted' as a spatio-temporal relationship. So, in simplest temporal logical terms, one layer recorded on top of another means the layer below must have existed at some period earlier in time in order for the upper layer to accumulate (or be deposited) on it.

Using such stratigraphic relationships we can then group archaeological deposits/strata into Phases, showing where various archaeological strata were occurring at similar 'periods' of time in the past and where a sequence of different periods, and the temporal relationships between them, may be recognized. A very simplified archaeological phasing might be characterized by "the Roman phase layers were deposited above (later than) the Iron Age phase layers, but the Roman layers are below (earlier than) the Early Medieval/Byzantine phase.

So to try and re-phrase my original question better.

Do astro-physicists have any similar (presumably more sophisticated) methodologies for representing the equivalent spatio-temporal 'Phases' e.g. perhaps the birth/death of different stars and galaxies at different 'phases' of the universe? Can any such 'phases' be displayed according to varying temporality in space-time within the images (cross-sections) of multiple celestial bodies?

If I imagine myself digging a vertical archaeological section, then looking at the geological cliff face below it, and then staring up into the night sky at the stars.

Is there any fundamental difference between a (3D or 4D?) stratigraphic section showing archaeological or geological layers laid down over thousands of years and an image of deep space with stars emitting light from widely different periods of time?

Thanks for any further ideas or references

Keith

Refs:

C. Lyell - Principles of Geology (1830)

E. Harris - The Principles of Archaeological Stratigraphy (1979)

Gavin Lucas 'The Archaeology of Time (2004)

Keith,

The uncertainties associated with measuring distances in space grow larger the further things are away.

All of the methods (apart from parallax) for deducing the distance to an object are beset by assumptions - some good, some not so good.

But having said that, there *are* distinct phases in the Universe's life, but they tend to be very unfamiliar to us.

For example, for the first few hundred thousand years of time, the universe was optically opaque - till it had expanded sufficiently for atoms to be allowed to exist, the Universe was a hot and opaque thing.

So, that's a distinct 'phase'.

Similarly, the first stars didn't pop into being immediately. But star formation *is* an ongoing process - so one cannot say 'stars formed at xyz date'.

(ooh, whaddayaknow, wikipedia saves me some effort!)

https://en.wikipedia.org/wiki/Chronology_of_the_universe

My take: there are very few identifiable stages (nothing like as many in terrestrial geology) and they tend to be associated with very different physical processes, rather than simply different ways of reworking the same material.

An interesting question though.

OK James,

That Timeline style of representation is just the kind of thing I was looking for. Thanks for the pointers from Charles and YOu. I'm going to absorb those and do some writing for now.

Keith, I think astronomy would be like anthropology if you were a million years in the future!  The difference in age between one layer and the next would be only a few centuries, and you would say all layers are contemporary.  You would say, 'people lived here.'

You ask, "Do astro-physicists have any similar (presumably more sophisticated) methodologies...?"          Yes, we do have - we ignore it.

Keith your initial question appeared inchoate, but looking at the responses it appears that you are mainly concerned with how distances for astronomical objects are discerned and the uncertainties. There is a general concept in basic astronomy of the distance ladder. We establish distances to nearby objects (through trigonometric parallaxes), determine new "standard candles," and expand the process until we arrive at red shifts for the most distant objects, which are luminous galaxies or quasars at cosmological distances. The recording in these processes involves first astrometry (careful measurement of positional shifts on the sky), then relative brightness of stars, clusters of stars, and galaxies, or galactic nuclei (involving careful measurement of luminous flux, and making use of the inverse square diminution of light with distance) and spectroscopy (to register the Doppler shift of receding galaxies).  The development of individual "standard candles," one of which --- the Cepheid pulsating variables --- was mentioned above, involves a much longer discussion, but I get the idea that you are not so much interested in those details. As to distance resolution, yes, as noted previously, in general the greater the distance, the greater the uncertainty.  To give you a peg, for nearby objects in the Sun's vicinity, out to a few hundred parsecs, the uncertainty is of the order of a parsec.  Does this do it?