by Ciro Santilli (@cirosantilli, 34)
Ciro Santilli likes to learn astronomy a bit like he learns geography: go down some lists of "stuff that seems most relevant in some criteria to us!", possibly at different size scales e.g.:
Looking at most astronomical object through a Telescope is boring because you only see a white ball or point every time. Such targets would likely only be interesting with spectroscopy analysis.
There are however some objects that you can see the structure of even with an amateur telescope, and that makes them very exciting.
Some good ones:
With Telescopes however, it is possible. www.quora.com/Can-we-distinguish-individual-stars-in-other-galaxies-or-would-it-be-equivalent-to-say-we-know-there-are-other-forests-of-stars-galaxies-but-we-cant-tell-the-individual-trees-stars-What-is-the-farthest-individual/answer/Jerzy-Micha%C5%82-Pawlak contains an amazing answer that mentions two special cases of the furthest ones:
But what we can definitely see are globular clusters of galaxies. E.g. the article en.wikipedia.org/wiki/Messier_87 basically gauges the size of galaxies by the number of globular clusters that they contain.
The Large Magellanic Cloud stands out as the brightest thing we can see from outside the Milky Way by far!
Some stars are so close that we can actually see their angles move with time due to the relative motion between them and the Sun, e.g. Proxima Centauri!
A fancy name for astronomy ;-)
Video 1.
CosmicPI: Detecting Cosmic Rays with a Raspberry Pi by Marco Reps (2021)
Source.
Sometimes it feels like this could be how we finally make experiments to see what the theory of everything looks like, a bit like the first high energy experiments were from less exotic cosmic rays.
Surely You're Joking, Mr. Feynman chapter An Offer You Must Refuse (a play on words on The Godfather (1972)) has an interesting historical mention from the early 1950s while at Caltech:
The next day, I had the greatest luck in making a decision. God must have set it up to help me decide. I was walking to my office, and a guy came running up to me and said, "Hey, Feynman! Did you hear what happened? Baade found that there are two different populations of stars! All the measurements we had been making of the distances to the galaxies had been based on Cephid variables of one type, but there's another type, so the universe is twice, or three, or even four times as old as we thought!"
I knew the problem. In those days, the earth appeared to be older than the universe. The earth was four and a half billion, and the universe was only a couple, or three billion years old. It was a great puzzle. And this discovery resolved all that: The universe was now demonstrably older than was previously thought. And I got this information right away - the guy came running up to me to tell me all this.
If you point a light detector to any empty area of the sky, you will still get some light.
The existence of this is quite mind blowing, since "there is nothing there emitting that light".
To make sense of how it is possible to see this light, you can think of the universe as the expanding raisin bread model, but it expands faster than light (thus the existence of the cosmological event horizon), so we are still receiving light form the middle, not the borders.
CMB is basically perfectly black-body radiation at 2.725 48 K, but it has small variations with variations of the order of 200 microKelvin: cosmic microwave background anisotropy.
There is a slight variation in temperature of CMB across the sky of the order of 200 microKelvin. It is small to the ~2.7 K average temperature, but it can be measured.
If the initial conditions of the Big Bang and the laws of physics were perfectly symmetric, then we could expect the Universe to just be one perfectly uniform boring soup.
But instead some asymetry made all the fun weird things we see today happen eventually, like galaxies and life.
And the cosmic microwave background serves as a way for us to look back in time to the early conditions of the universe, as it was set in stone as soon as the universe became transparent to this light during recombination.
Or if you want to get poetic, it is the closest we can ever get to listening to the original word of God when he setup the initial conditions of the universe.
The ansiotropies of CMB is the ultimate astronomical compass we will ever have, as it is the thing with the least proper motion.
Figure 1.
Cosmic microwave background anisotropy measured by the Wilkinson Microwave Anisotropy Probe
. Source.
Figure 1.
Cosmic microwave background anisotropy measured by the Wilkinson Microwave Anisotropy Probe
. Source.
If looking through these don't make you think of the Book of Genesis then nothing will.
Figure 1. Source.
What an awesome list the dude compiled. Contains many of the features we care the most about of the sky, since of course, apparent magnitude is a big determinant of that.
Interesting to note that there are quite a few nearer than Sagittarius A, as of 2022 we know of one at 1.5 kly: universemagazine.com/en/discovered-the-closest-black-hole-to-the-sun/
It is interesting that a few months earlier there seemed to be no known specific black holes in the Milky Way: www.nasa.gov/feature/goddard/2022/hubble-determines-mass-of-isolated-black-hole-roaming-our-milky-way-galaxy although their count is estimated to be in the hundreds of millions.
For comparison, remember that the Milky Way is 185 kly in diameter x 2 kly thick.
Cover up the entire sky in a compatible way with the traditional constellations. They are also very square, the boundaries consisting only of vertical and horizontal lines on the sphere.
Basically a mini-Constellation.
Video 1.
Celestron NexStar SE Tutorial by Astronomia UK (2022)
Source. Meh! ;-)
Alignment is impossible to get right! Tried 3 star, 2 named stars, and neither worked well.
Composed mostly of the Virgo cluster and the Local group.
Some major ones:
The basically composed of only the Andromeda Galaxy and the Milky Way. Every other galaxy is a satellite of those two.
Figure 1. Source.
First proper nearest galaxy to the Milky Way. Everything in the middle in the Local group is either a satellite of the Milky Way or Andromeda.
Many Andromeda satellite galaxies are simply numbered Andromeda II, Andromeda III and so on.
As described on Wikipedia, the observational history of Andromeda is fascinating. Little by little, people noticed that it had a different nature to many other objects observed on the sky, and the hypothesis that there are other galaxies like ours grew in force.
Part of our fascination with Andromeda is due to how similar in size and shape and close it is to the Milky Way.
It is clearly the only thing so large and so close.
Andromeda is, without a doubt, our sister galaxy.
One can't help but wonder if there is some alien looking back at us when we are looking at them through our Telescope.
Andromeda is also the furthest object from Earth that can be seen with the naked eye.[ref] Not surprising, as it literally shines with the strength of a trillion suns!
Figure 1.
Highest resolution image of Andromeda as of 2015, taken by Hubble
. Source. Source also says it was the highest resolution image every released by the Hubble. This goes to show how fascinated people are by Andromeda. And there is good reason for it.
Video 1.
Andromeda Shun from Saint Seiya performing his Nebula Chain attack
. Source. The original Japanese music actually says "Nebula Chain" in English. The Andromeda Galaxy is shown on the back, the chain appears to go all the way to it and back towards the evil guys' head. Not very relativistic, but so be it.
Video 2.
Andromeda Galaxy with only a Camera, Lens, & Tripod by Nebula Photos (2020)
Source. Good job! Gives a good idea of the low end approach.
Figure 1.
Arms of the Milky Way
. Source.
The first proper galaxy near the Milky Way is the Andromeda Galaxy. Everything else in the middle is a satellite of either of of those.
One of the brightest natural objects in the sky, and by far the brightest not in the Milky Way! This is partly because it is relatively close to us.
It is so close that we can notice its proper motion, and its distance to us will vary significantly across a few tens of thousands of years!
This is quite close! But as mentioned at: stars nearest to the Sun, there are several others nearby. Notably Sirius at 9 ly, the brightest star in the sky as of 2020.
Figure 1. Source.
Figure 2.
Distance of stars nearest to the Sun as function of time
. Source.
Some notable ones:
  • Proxima Centauri, the nearest one, at 4 ly. It is part of the Alpha Centauri star system, which contains two other stars at very similar distances as well, and their relative distances to earth will change positions in a few tens of thousands of years.
  • Sirius, the brightest star in the sky at 9 ly

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