What about stars? Is it like looking off in the horizon and trying to determine if a large island is 100 miles away or a small island 20 miles away?
You can measure the distance of an island by triangulation. You use surveyer's instruments to find the angle to a point on the island from two different locations on the shore. That gives you a triangle, with apex on the island, and the baseline as the straight line between the two observation points. Solve this triangle using the methods of high school trigonometry, and you have the distance to the island.
What I'd discovered was that lightyears are not a measurement of time, but of distance.
I already knew that when I was in elementary school.
The distance to the sun is also measured by triangulation. You do need a larger baseline, so the measurements are made from points on earth that are a large distance from one another.
The nearer stars are measured by triangulation, using the axis of the earth as a baseline. You can measure the angle to that star at two different times, 6 months apart. For more distant stars other methods are needed, but I'll omit the details for now. You can find them described in other threads in this forum.
The long and short of this, is that the great distances to stars are real. Astronomers are not making this up, and are not merely guessing.
Challenging and accomplishing such a feat was the NEC Institute at Princeton University who were able to greatly exceed the standard of 186,171 mps.
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That report is about group velocity. It is well known that group velocity can exceed the velocity of light, and this does not challenge any of our physics. Nor does it challenge the theory of relativity.
As well, a team at the Rowland Institute at Harvard yielded impressive results when they were able to bring light to a crawl. Imagine seeing a beam of light in midair that has yet to illuminate the other side of the room.
http://www.gsreport.com/articles/art000084.html
There is nothing new in the idea that light can travel more slowly, although the particular research did show how to slow it down far more than had previously been achieved. The way a camera lens works already depends on light slowing down as it passes through the lens, and this has been known since well before the theory of relativity was formulated.