I don’t mean “when did we realize there were other planets and the sun was just another star?”
I mean when did we realize how big the sun was and how vast the distances between planets and stars was? When did we start to discover the scale of the universe and how freaking impossibly huge it all is? When did we begin to understand that our little mudball was a microscopic dot on a microscopic dot on a microscopic dot?
Nitpick: I don’t consider the Milky Way to be a microscopic dot compared to the rest of the visible universe. It’s more of a macroscopic dot. If the visible universe were a large building, the Milky Way would be a visible dot even if it weren’t a point source of light. Whereas if the Milky Way were on the same scale, the Sun may or may not be visible as a point source of light, but it would be many orders of magnitude smaller than the difference between the Milky Way and the universe.
It started with telescopes, pretty much.
Galileo discovered the four big moons of Jupiter in 1610. That was the first time a satellite had been observed around another planet, and confirmed that the other planets were similar somehow to Earth.
Johannes Kepler and Isaac Newton developed the mathematical models of orbiting bodies (assisted from the voluminous observational data compiled by Tycho Brahe and others.)
The birth of spectroscopy in the 19th century allowed us to learn that the sun was composed of hydrogen and helium.
In the early 20th century, the prevailing view was that the entire universe consisted of the Milky Way galaxy. Better telescopes put that notion to rest. Edwin Hubble and others observed that what we thought were nearby gas clouds in the Milky Way were actually distant galaxies consisting of billions of stars. Hubble also used redshift calculations to figure out how fast these galaxies were moving away from us. That was the beginning of the present “holy shit, this thing is huge” era of cosmology.
Einstein developed general relativity to explain observations of the universe that didn’t fit in with Newtonian mechanics. Einstein believed that the universe was “static,” essentially an unchanging, empty space dotted with occasional chunks of matter. The math of general relativity didn’t quite match up with that view, so he kludged in a “cosmological constant” to make it work.
It turns out Einstein’s original calculations were correct and the cosmological constant was a mistake. We now know that the universe is not static, but expanding all the time. That leads to the conclusion that it was much smaller in the past, and must have started with a big initial expansion.
In 1964 Penzias and Wilson accidentally discovered cosmic microwave background radiation while working on a bigass horn antenna for Bell Labs. The radiation had been predicted based on Big Bang theories but had never been observed.
Still later we’ve been able to build bigger and bigger radiotelescopes to observe radiation from galaxies and other objects at incredibly vast distances.
It’s hard to believe that just 500 years ago most educated people thought the universe looked like this.
Didn’t Einstein’s cosmological constant turn out to be true? Isn’t that what dark energy is, sorta kinda?
The scale of the universe was still being debated as recently as 1920, when astronomers Harlow Shapley and Heber Curtis had what became known as Great Debate. Shapley’s position was the prevailing position at the time, that the Milky Way galaxy was the whole universe, and the spiral nebulae we could see here and there were just nearby gas clouds in the Milky Way. Curtis’s position was that the Milky Way was just one of many galaxies, and that the spiral nebulae were actually very, very far away galaxies just like our own. A couple of years later, Edwin Hubble proved that Curtis was right, and that the spiral nebulae were actually what we now know to be the Andromeda galaxy, the Pinwheel galaxy, and so on. The notion that our own galaxy is just one out of countless others is so basic now it’s strange to think that less than 100 years ago it was the subject of vigorous debate at the highest levels of astronomy.
ETA: or, kinda what friedo already said in his 4th paragraph. 
Kinda. See the Positive value section of the Wikipedia article. Basically, tweaking things by using a small positive value can help to explain observations related to the accelerating expansion of the universe. But there are a lot of gaps in our knowledge and the theoretical models are still incomplete.
If the Earth orbits around the Sun, the “fixed” stars would change their relative positions due to parallax. Among ancients, it seems that only Aristarchus of Samos developed the proper explanation: The Earth does orbit, but the stars remain fixed because they are at an unimaginably huge distance.
Eighteen centuries after Aristarchus, Copernicus found the same explanation, though it still took time to be accepted.
This page has some interesting data on efforts to find the scale of the universe.
http://ned.ipac.caltech.edu/level5/March02/Gordon/Gordon2.html
The first people to write about the idea of other galaxies outside the Milky Way were Swedenborg and Wright in the early 18th century.
William Herschel did a mammoth analysis of the density of stars in the Milky Way, and came to a rough estimate of it’s size; at first he agreed with Swedenborg and Wright that certain nebulae were collections of stars with equal rank with the Milky Way, and this led him to arrive at a reasonably accurate distance to some nearby galaxies.
However he later changed his mind, since he noticed that some nebulae were associated with a single star. If he had only been able to determine the difference between nebulae which are other galaxies and nebulae which are within our own galaxy he might have been able to establish the size of the Local Group quite accurately.
I would submit that the size of the universe is unknown. There is, of course, the “known universe,” that seems to have some sort of generally accepted value to cosmologists, etc., but inasmuch as philosophically, at least, distance from the earth is infinite, there’s always the question of does it EVER end? Hence, no one really knows the size of the universe.
Do you have a cite for the claim that Aristachus was concerned with stellar parallax? The evidence that he even believed in a heliocentric solar system is rather meager, and certainly, given the large inaccuracies in astronomical measurements in his time, the stars would not have to be all that far away to show no measurable parallax. We do know that Aristachus tried to estimate the relative distances of the Sun and Moon, and (despite the theoretical soundness of his method) in fact vastly underestimated the distance to the Sun, due to measurement inaccuracies.
It is true that Copernicus was concerned by the lack of measurable stellar parallax, and as a consequence postulated that the stars are very much further away than the most distant planet (Saturn, as was then thought). Picking up on this, Thomas Digges and Giordano Bruno suggested that the stars might be distant suns, scattered through space, perhaps with their own planetary systems. (Digges was first to suggest this in print, I think, but he was not widely read. Bruno, whose works were quite widely read, probably came up with the idea independently, and so was probably much more influential.) Copernicus himself still thought, like the ancients, that the stars were lights on a the inside of a huge sphere surrounding the solar system; he just thought the sphere must be bigger than they had thought.
So, in a way, the first major expansion of the universe since ancient times, and into something recognizably like its modern form, was due to Digges and particularly Bruno. Of course, the trouble was that there was essentially no evidence for any of this (including basic Copernican heliocentrism) until a generation or more later, with the work of Tycho Brahe, Kepler, and Galileo. Bruno liked Copernicus’ ideas not because of any empirical or mathematical evidence, but because he (Bruno) was a religious whackjob who thought the idea of a much bigger universe, and perhaps other planets with aliens on them, was really cool. By sheer luck, he got things right.
That lack of observation of parallax was the objection to heliocentrism may be an assumption of historians, but that Aristarchus’ heliocentrsim (which is known via the writings of Archimedes) postulated a large distance to the stars seems clear:
(The 3rd paragraph here seems muddled to me, although Archimedes somehow constructs a hypothetical size from it, and uses this for “Sand Reckoning.”)
Aristarchus? He got it from me. When I was just a boy, I looked up and said “Hoo boy, there’s a lot of room out there.” thank you.
The 2,000 year-old man.
There’s the POV that Columbus screwed up big time. The Greeks worked out that the earth was a sphere, and the rough diameter was 8,000 miles. (Nobody educated really thought it was flat) A contrary Greek philosopher worked out that the world was only 4,000 miles or so in diameter. The story goes that Columbus subscribed to this contrary view and then took a close look at Marco Polo’s book. Estimating the distance Polo went, and his version of the earth’s diameter, he figured that Cathay was only 2,000 or 3,000 miles west from Spain. Good thing the Americas were in the way.
So the people who wandered around a few hundred miles of known seashore accepted that earth must be a ball about 8,000 miles across.
The definitive proof was Newton’s theory of gravity. If you accepted that the same force made things drop on earth at 32ft/sec^2 was also responsible for the moon orbiting in 29 days, and the earth orbiting the sun in 1 year - then plugging the numbers into Newton’s equations meant that the moon was a quarter of a million miles away, and the sun impossibly 93 million, with resultant values for planets.
and so on… How far away does something have to be before there is no noticeable parallax across the globe? Scary numbers!
Any chance you can either write out that proof or direct us to a clear exposition of it?
Are you saying you could calculate the Earth’s diameter? You’d need to already know the radius of the Moon’s orbit. (How accurately was that known?) Or you could get the Moon’s radius if you knew Earth’s diameter. But you need to know one. You can’t get both.
How could an astronomer in Ancient Greece estimate the distance between the Earth and the Sun? I suppose they could figure out the Moon because they had an estimate of Earth’s diameter already and could measure the shadow Earth casts on the moon during a lunar eclipse.
I own a children’s book called The Book of Wonders that belonged to my late father. It contains a bunch of photos with brief text descriptions of engineering and scientific marvels (or what counted as marvels in the late 1920’s.)
On one page there’s a beautiful photo of the Andromeda galaxy which is described as a whirlpool nebula that some day will become a solar system.
I meant the radius of the Moon’s orbit here.
Aristarchus estimated the relative distances of Moon and Sun by noting that during a half-moon the Sun Earth and Moon must form a right angled triangle (with the Moon at the right angle). He could then measure the angle between Moon and Sun, and then from simple geometry get all three angles, and then with a bit of proto-trig, get the relative (not absolute) distances of Sun and Moon. The method is sound in principle but unfortunately, as I said, the measurements (including, probably, the judgement of when the Moon was at exact half phase) were way off, and he vastly underestimated the distance of the Sun, putting it, IIRC, only about 6 times as far away as the Moon.