If you like science history or just want to understand the universe better, I recommend Everything and Nothing, the Amazing Science of Empty Space, which is a free documentary if you have an Amazon Prime membership.
Science, philosophy, history: all of that is mixed into this documentary that tries to conceive just how big space is. You will be surprised when you discover just how small we are compared to everything else.
How did we figure out that there are more galaxies than just the Milky Way?
Did you know about Henrietta Swan Leavitt, the woman behind Hubble’s discovery of the distance to the Andromeda galaxy?
A strong direct relationship between a Cepheid variable [star’s] luminosity and pulsation period established Cepheids as important indicators of cosmic benchmarks for scaling galactic and extragalactic distances. This robust characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds. This discovery allows one to know the true luminosity of a Cepheid by simply observing its pulsation period. This in turn allows one to determine the distance to the star, by comparing its known luminosity to its observed brightness.
We’ve made notable progress in mapping the universe. Not really, but compared to our past supreme lack of knowledge we seem to know more now.
A team of researchers working with the Baryon Oscillation Spectroscopic Survey (BOSS) has determined the distances to galaxies more than 6 billion light-years away to within 1 percent accuracy — an unprecedented measurement.
Sounds great, but 1% error is quite a lot at the size of a universe.
The image below is both the oldest and youngest picture ever taken.
It is the oldest because it has taken the light nearly 14 billion years to reach us. And it is the youngest because it is a snapshot of our newborn universe, long before the first stars and galaxies formed. The bright patterns show clumps of simple matter that will eventually form stars and galaxies. This is as far as we can see into the universe. It is time, not space, which limits our view. Beyond a certain distance, light hasn’t had time to reach us yet.
The size we can discern is mind boggling, and it seems to be expanding at an ever increasing rate.
It is estimated that the diameter of the observable universe is about 28.5 gigaparsecs (93 billion light-years, 8.8×1023 kilometres or 5.5×1023 miles), putting the edge of the observable universe at about 46.5 billion light-years away. The total mass of ordinary matter in the universe can be calculated using the critical density and the diameter of the observable universe to be about 1.5×1053 kg.
No one knows if, beyond the edge of the observable universe there are infinite stars, and as if infinite wasn’t enough, some believe there is evidence that ours is just one of a collection of (endless?) universes!