I have a vague memory of a time early in my life where I thought my neighborhood had it all. The house I lived in, my friend down the block, the playground, my church, the grocery store, the pizza spot, the McDonalds, and every restaurant I had been to (I was very into food at this point of my life). I Found it difficult to imagine anything outside of this that I needed. My father worked in aerial photography, letting me see photos of Denver from the air inspiring the notion there was more out there. When I visiting a playground across town, I started to think that everything else was all more of the same, Denver maybe had a few neighborhoods each one with a playground, I of course wanted to see them all to make sure I had the best.
I had a globe but never saw it as more than a spinning toy till I was shown on it where my grandmother lived (Texas). I then got somewhat of an idea of what all was out there, how many playgrounds I have yet to see. I’ve traveled a bit of the world now but I’m still reminded of how tiny that bit is all the time. Even at home, I have lived in Colorado for the vast majority of my life and still find surprises in my own backyard. Collectively humanity has been discovering the universe in a much similar way.
In biblical times the sky was seen as a solid dome and the Earth a flat plane below it. Genesis 1:6-8 (written between the 6th and 5th centuries BC) describes the creation of the sky: “Then God commanded, ‘Let there be a dome to divide the water and to keep it in two separate places’—and it was done. So God made a dome, and it separated the water under it from the water above it. He named the dome ‘Sky.’ ”.
The word for sky was firmament which you can break down and see the word ‘firm’ showing the idea of the sky as a solid. This is a Latin word translated from the Greek stereoma meaning “solid dome” which is a translation from the Hebrew rakia meaning “thin metallic sheet”
In the later Revelations 6:13-14 (written ~90 CE) the sky is described as rolling up and the stars falling off it “The stars fell down to the Earth.... The sky disappeared like a scroll being rolled up…”
In the 5th century BC Greek philosophers were starting to pick up on the Earth being round and imagined the sky as a round sphere that spun once every 24hrs around the round. The stars were seen as fixed to the sphere and the planets, Sun, and moon wandered around the sphere.
There were a few Greek scholars that around the 3rd century BC that suggested other ideas. Democritus of Adbera who in 490BC speculated The milky way was made up of many small stars. The common thought of the time was that the milky way was a luminous fog on the sphere of the sky. Even Aristarchus of Samos in 260BC was the first known to suggest the planets revolve around the Sun, not Earth. However these speculations didn’t gain traction in their time as most were happy with the sky being a giant sphere revolving around the Earth with everything else in the sky. It wasn’t till very recently (in the context of time) that we started to shape how we see the sky to this day. Astronomer Nicolaus Cusanus (in 1440), and italian Giordano Bruno (in the late 1500s) introduced us to the notion of space being a place stretching infinitely, and all the stars are much like our Sun so far away we just see them as specks of light. Introducing this idea was not easy as the solid sphere model had been heavily ingrained in the minds of the masses.
In 1543 astronomer Nicolaus Copernicus pointed out that placing the Sun in the center of the planets made it easier to predict the future positions of the planets. However, this was seen more as a mathematical trick and didn’t persuade people to really viewing the Sun at the center. Many who thought the Sun in the center of the planets still thought of the stars as fixed to a sphere. Once Galileo Galilei started exploring the heavens in 1609 with a telescope that evidence for both of these speculations started to pile up. Looking at the milky way he saw that it truly was made up of countless faint of stars. Looking at Jupiter he saw that it had 4 moons that orbit it independent of the orbit around the Earth, and seeing Venus has phases just like our Moon was much easier described by having the Sun in the center rather than the Earth.
Also in 1609 astronomer Johann Kepler refined the model of the Sun centered (heliocentric) solar system by showing mathematically that the planets orbit the Sun in ellipses, not perfect circles. This means we drift closer and further to/from the Sun, and planets at different points in our orbit. This can be seen in “super Moons” which appears larger than the regular full Moon because the Moon happens to be on the point on its elliptical orbit that makes it closer to Earth.
Astronomer Giovanni Domenico Cassini in 1672 made the first measurements to the size of the solar system. He estimated Saturn (the farthest known planet at the time) to be around 3 billion kilometers away. This was way larger than anyone at the time would have guessed.
None of this changed the concept of what was beyond the planets. It wasn’t until 1718 when astronomer Edmund Halley was making a new star map and found some stars (Prycon, and Sirius from a blog post a few weeks ago) had moved a little. Ancient Greek star charts had them placed slightly differently among the dimmer stars than what Halley was observing. This showed that the stars were moving too!
Halley picked up the speculation that the stars were just like our Sun but far away. Assuming Sirius is the same brightness as our Sun Halley calculated it would have to be 2 light years away (making him the first to measure distances in light years). Sirius is much brighter than our Sun so this was way off, Sirius is more like 8.6ly away.
In 1838 to get a real Idea of the distance to the stars astronomer Friedrich Wilhelm Bessel used paralax. Just like your two eyes gives you depth perception, parallax gives astronomers depth perception to the stars. If you look up at a star close one eye and cover it with your thumb then, switch eyes you will see your thumb move and no longer cover the star. Your brain takes these two images and realizes your thumb is closer than the star because it moves. To do this with the stars we need two images from much further apart, and our orbit around the Sun gives us that. If we take a picture of the sky tonight then, wait 6 months when the Earth is on the other side of the Sun, halfway around our orbit, and take another picture we’ll have two images of the sky from each side of the Sun. Now comparing these two images we might notice some stars move very slightly while others appear to not move at all. Knowing the Earth-Sun distance and the angle at which the closest stars move we can get a highly accurate measurement of the distances to the stars.
Bessel found these distances to be astonishingly huge! The closest Alpha Centauri was 4.3 light years away. In doing so Bessel finally smashed the idea of a sphere with stars outside the planets, and tremendously increased the size of the Universe.
Measurements of the galaxy started to take shape looking at the milky way which makes a circle around the sky it was apparent that stars preferred this region of the sky. Scholar Immanuel Kant in 1755 proposed that just like the planets orbit the Sun in a flat ring maybe the stars orbit the milky way in a flat plane. He also concluded because the milky way extends all the way around Earth we must be towards the center of the galaxy. In 1785 astronomer William Herschel confirmed Kant’s speculation by taking a survey of the stars. He called this star system we are in the “galaxy”. Nebulae were well known and studied objects at the time, while categorizing nebula there were some known as ‘spiral nebulae’ that didn’t quite fit. Some of these nebula such as the Magnetic clouds and “The great nebula in Andromeda” could be seen with the naked eye. Kant proposed that these were other star systems or “Island Universes”. This conjecture was debated among astronomers until 1936 when astronomer Edwin Hubble, using the new 100-inch telescope, was able to estimate the distance of these nebulae and found them to be much further than any thing that could be within our own galaxy.
Like my realization that I will never get to visit every playground, in 1936 was when accepted everything we know, our galaxy, was just a tiny fraction of what was out there. Our Earth is no longer in the center of the planets, our Sun is no longer the center of our galaxy and our galaxy is no longer unique. As of 2016 NASA estimates there to be 2 trillion galaxies in the observable universe.