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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:
Bibliography:
en.wikipedia.org/wiki/List_of_brightest_natural_objects_in_the_sky
We can't see individual stars outside of the Milky Way:
Any single star outside of the Milky Way cannot be seen.
The Large Magellanic Cloud stands out as the brightest thing we can see from outside the Milky Way by far!
With telescopes however, it is possible apparently. See e.g.:
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.
The existence of this is quite mind blowing.
It is basically perfectly black-body radiation, with a very faintly by measurable anisotropy (slightly less or slightly more some regions) due to quantum fluctuations of the early universe.
To make sense of it, 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.
The ansiotropies of CMB are likely the best astronomical compass we will ever have, as it is the thing with the least proper motion.
expansion of the universe
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.
www.celestron.com/
Video 2. 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:
noirlab.edu/public/images/noao-m49/?nocache=true also lists: M58, M59, M60, M61, M84, M85, M86, M87, M88, M89, M90, M91, M98, M99, and M100 so lots of large and easily observable galaxies in the area.
The basically composed of only the Andromeda Galaxy and the Milky Way. Every other galaxy is a satellite of those two.
Figure 2. 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 3. 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 3. 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 4. 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 4. 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 5. Source.
Figure 6. Distance of stars nearest to the Sun as function of time. Source.
upload.wikimedia.org/wikipedia/commons/e/e9/Near-stars-past-future-en.svg
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
This section is present in another page, follow this link to view it.
Good list: en.wikipedia.org/wiki/Geologic_time_scale#Terminology
As usual, blame the Russians.
archean/proterozoic barrier.
The term "visible life" refers to multicellular from before people knew there was life in the proterozoic.
This period is similar to the Quaternary, but it also includes tool usage by close relatives of humans which were not humans yet.
It ends together with the pleistocene.
Agriculture is not the official definition of the age. But it is good enough. Likely related to the official end of glaciations thing.
End: Permian-Triassic extinction event.
No life, earth too hot, until formation of water.
Made up mosty of calcium carbonate.
Not done yet as of 2020! Will be done one day for sure.
Can you imagine when those guys started to see moons in other planets? They must have shat bricks. What better evidence can you have that the geocentric model could be wrong?
Figure 7. Source.
The first planet not known since antiquity.
Quite cool how it was discoverd by the perturbation of Uranus' orbit.

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