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I have been wondering, maybe some one could enlighten me as to the answer I have been looking for. I have googled, but I am after a more direct answer to this question.

If light takes X time to travel a distance, and some of these distances are so vast it would take so called millions of years for that photon to travel, how can we possibly have measured that since our technology really has been good enough in the last 20 - 30 years to get any real accurate measurements?

The other problem I have with the question is if we don't send the original light emission for the bounce back how can we possibly be sure what data we have is even remotely accurate?

If we can't be accurate or the data is corrupted due to false or innacurate data collection how can we truely know where we are for accurate space exploration beyond our region of viewable space (our set of planets, not the Milky Way as a whole) as we could not possibly guage the speed at which we - the Earth or the opposing planet - is actually travelling or rotating axis based on their own centre of galaxy or orbit>?

Is there an answer for this, or am I thinking about this way too hard?

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    $\begingroup$ This is probably more suited to the Astronomy stack, but a very quick Google gives you How Do You Measure The Distance To A Star $\endgroup$ – Snow Apr 7 at 10:36
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    $\begingroup$ Much of what you are asking about is really about Astronomy and how science and physics over the millennia has allowed us to make these measurements. You might get more detailed answers from an Astronomer or Physicists, but I'm sure one of those will come along soon and help you understand the science behind such measurement. $\endgroup$ – Brian Tompsett - 汤莱恩 Apr 7 at 10:36
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    $\begingroup$ This question is off topic for this site. From the help center, "Space Exploration is primarily about spacecraft, how to send them to space, and their functions there." You should instead be asking this question at the Astronomy or Physics StackExchange, but I'm sure this question has already been asked and answered at both of those sites. $\endgroup$ – David Hammen Apr 7 at 11:48
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    $\begingroup$ It's not relevant to navigation. Voyager 1 has traveled further than any other probe or spacecraft, and is only a bit over 9 light hours away. No spacecraft can travel further than can be measured directly with round-trip lightspeed time...obviously, they move much more slowly than light. $\endgroup$ – Christopher James Huff Apr 7 at 12:55
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    $\begingroup$ I don't know, but I suspect that part of the reason there was some pushback here (down votes and close votes) might be related to the "...or is it just a hoax?" in your title. If you want to question whether spaceflight is a hoax or not, then the question will be closed as off-topic. If you don't want to question if spaceflight is a hoax then you should not have written that. "Proper educated folks" don't go usually around suggesting things like this are hoaxes. space.meta.stackexchange.com/search?q=hoax $\endgroup$ – uhoh Apr 7 at 18:36
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Working outward, initial measurements were based on measuring angles and a lot of math working from orbital motion which got a consistent model of the solar system, and indeed located planets because the math was inconsistent. This has been fine tuned with LASER measurement to mm accuracy to the moon, and radar measurement of planets out to Saturn. With positions and motion within the solar system known parallax measurement allows nearby stars to be ranged (where near is '10,000 light years').

This is the foundation that the Cosmic Distance Ladder sits on, which turn depends on some physic phenomena that cause Steller behavior to be fixed, in particular the standard candles where the known intensity of events can be used to determine range by measuring observed brightness at Earth.

For speeds the fixed spectra lines of compounds absorbing light can be used to determine Doppler shift.

As noted speed of light means that for more distant observations these events are those that happened in the past, so the assumptions are built on nothing in the laws of physics having changed over that intervening period.

So far the simplest model is that the constants are indeed constant but it is certainly possible to construct complex models that have for example the absorption spectra of stars changing in the distant past/far distance and which would change the shape of the observed universe. This is a case where all we can do is apply Occam's Razor and look for discrepancies in our local measurements over human time scales .

If curious a number of the nearby measurements that were previously a lifetimes work for teams of astronomers are achievable with basic equipment.

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    $\begingroup$ Thank you @GremlinWranger, these links are great resource, many thanks for this i found this answer to be very fulfilling. thank you for your time! $\endgroup$ – Maize Apr 7 at 12:15

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