For primitive enough experiments, yes, the distance of the Sun is derived even more directly than that of the Moon.

First up to bat is Aristarchus (or, rather, he's usually given credit). The Sun shines down into a well at Noon where he is. A friend a few hundred miles North finds the Sun is several degrees off from being able to shine down a well.

If you assume both wells are on the surface of a sphere, and the Sun is at infinite distance (at least to within the error bars of this experiment), you can use this to solve for the circumference of the Earth. Which he did. And the wells might not have been perfectly plumb, and the distance from one well to the other was estimate by people who walked there following trade routes...but the errors happened to cancel out in his favor and he got the number about right.

Now we have the distance to the Moon. Using primitive observational equipment (naked-eye, no decent chronometers), there's no way you can figure it out from parallax. But...you can observe a lunar eclipse.

Even a partial eclipse shows, clearly, the round edge of the Earth as a shadow on the Moon's track. And you can figure out the size of that shadow, and with basic geometry, you know how far away that shadow is (based on how big around you previously figured the Earth was!) And that tells you the distance to the Moon.



But then we have to bump forward over a thousand years. To Sir Isaac and universal gravitation. Assuming (as he did, and as we still do), that gravity is the same throughout the universe, you can calculate how far an object needs to be from a particular mass (like the Sun) to have a particular orbital period.

He could plug in the known distance of the Moon, and by expanding the ratios, come up with a distance for the Sun that made not just the Earth, but all the planets orbit at their observed periods.

I'm simplifying a bit at this point, because then we embark on the dizzying journey of the stellar ladder, but we also start to bolster these kind of basic pre-telescopic observations with radio astronomy, space probes, and of course optics precise enough to actually measure the parallax of a star.

A very close star, that is. In fact, the closest star to us that isn't a red dwarf. The Moon as visible from Earth occupies a half degree of arc; what is called thirty minutes of arc. These devices could measure down to a difference of a second of arc. And it just so happens that if you spend six months making the observation, you can observe Alpha Centauri moving against the background stars by that second of arc.

A parallax of one second. A par-sec.





When I saw this thread, I thought the Punisher-bot had just discovered Olber's Paradox. Now that might be interesting!

But I wonder if we aren't missing something else about the hypothetical dust spec. Unlike the thousands of km the Earth has for a diameter, a dust spec is of a size that is close to the wavelength of visible light. This means light can actually bend around it. You have to get down to energies like the CMBR before a wave function will bend around the Earth!