Astronomy 101

In the spring of 2020, The Event happened. With everyone stuck at home and not being able to see anyone, online resources boomed. In an effort to keep myself sane, and to share my love of astronomy, I started offer (mostly) weekly public talks about various astronomy-related things. I talked about the life and death of the Universe, about my research project, about where life is in the Universe, what the Star of Bethlehem could’ve been, and some more complex things, like an introduction to dark matter, spiral galaxies, and a tour of the solar system.

However, while those presentations were good, they were sometimes aimed a little too high for my audience. Essentially, I was giving talks I would’ve given to a class of astronomy majors rather than the general public. The astronomy talks went on hiatus during the winter holidays so that everyone could spend safe, socially distant time with their families and so that I could recuperate from having to come up with a talk every week.

The astronomy talks have now returned in the Spring of 2021, nearly a year after The Event. This time, my goal is to rectify some of the mistakes I made the previous year. To do that, I’m calling these talks “Astronomy 101.” As the name suggests, I’m starting everything from a more basic level, spending time walking through basic mechanics, the nature of light and matter, and then moving on to the solar system and diving into stars and galaxies. Basically, I’m walking through the textbook The Cosmic Perspective.

Furthermore, in an effort to be considerate of people’s time, if someone is unable to attend the in-person virtual ecture (what a weird combination of words), I have pre-recorded each lecture and posted them to YouTube for people to watch at their leisure. This will be a landing page for those videos, keeping them updated with a summary of each (roughly) hour-long video.

The first in the lecture series is titled "Introduction to the Universe." In this talk, we cover the size and scale of the Universe, in both space and time dimensions. We also talk about the various motions the Earth goes through: rotating on its axis, orbiting the Sun, the Sun orbiting the center of the Milky Way, as well as moving randomly with respect to the local stars, and the Milky Way moving in an expanding Universe. We end with a brief discussion of the human adventure of astronomy. (Presented on February 28, 2021)
The second in the serities is title "The Night Sky." Here, we talk about how we understand the things we see in the night sky given our understanding of the Universe. We talk about the celestial sphere, why stars change depending on the time of year, and how the seasons work. We also go into detail about the phases of the Moon and how both lunar and solar eclipses work. We end by mentioning the weird apparent retrograde motion the planets go through and hint at what the Greeks attempt to solve in next week's talk. (Presented on March 7, 2021)
Any good astronomyt eacher will tell you that eventually we have to talk history. In this "The Science of Astronomy" lecture, we delve into the ancient Greek origins of astronomy, talking about the geocentric model of the Universe. Then we delve into the Copernican revolution and talk about the personalities of Copernicus, Tycho, and Kepler. Especially important are Kepler's Laws of Planetary Motion! We end with a discussion of what makes science science. (Presented on March 14, 2021)
To talk about the goings-on in the Universe, it is necessary to have an understanding of "Motion, Energy, and Gravity." Here, we talk about just that! We spend some time getting our definitions straight, before moving on to the man of the hour, Isaac Newton, and his laws of motion. We explore the deeper truths that are the conservations laws and how to apply them. Then we talk about gravity and explain how gravity works to create orbits, the tides, and Galileo's Leaning Tower of Pisa experiement. (Presented on March 21, 2021)
Except for a few objects, astronomers can't go to an object and physical measure its properties. That's why its important to understand how "Light and Matter" interact and how we can deduce the nature of an object from the light it emits or reflects. We talk just about that in this lecture, covering the types of spectra, and how we can tell the composition, temperature, and motion of an object from its light. (Presented on March 28, 2021)
Last week we talked about all of the information we can learn from light, now we need to talk about how to collect that light and that means "Telescopes!" Essentially astronomers want telescopes to be the biggest they can be to maximize light-collecting area and to minimize the angular resolution. We talk about how astronomers use those telescopes to do imaging observatiions, spectroscopic observations, and timing observations. We also explain the three main reasons why ground-based observing is limited and explore the wide variety of telescopes we put in space to observe the entire electromagnetic spectrum. (Presented on April 4, 2021)
We've finally done it! We've finished with the basic physics lessons and we can move on to give an "Introduction to the Solar System!" Here, we introduce the idea of comparative planetology and use it to describe the four types of basic patterns we see in the solar system. In order to do that, we go through a brief tour of the planets, the first and last time we will do that in this series. We end by describing the types of spacecraft that we use to learn about the planets and other objects in the solar system. (Presented on April 11, 2021)
We sort of ended last week on a cliffhanger, having talked about all of these large-scale patterns that we see in the solar system without explaining how they came to be. We attempt to do just that by explaining the "Formation of the Solar System." We cover the nebular theory and how it accounts for those patterns very well. We show the pieces of evidence, both observational and computational, that suport the theory as well as explaining that this wasn't all "planetary destiny." We end with a brief talk on radiometric dating and the age of the solar system. (Presented on April 18, 2021)
In this talk, we make our first attempt at comparative planetology by discussing the general geological processes that have shaped the "Planetary Geology" of each terrestrial world and then diving into how those processes explain the features we see on each world individually. We find that Mercury and the Moon are both heavily cratered worlds with no geologic activity as of late, that Mars is slowing down in its geologic activity, and Venus and the Earth should both still be geologically active! (Presented on April 25, 2021)
After having discussed the surfaces of the terrestrial worlds, we now move to a discussion of their "Planetary Atmospheres." Using the Earth as a template to our understanding, we discuss the basic atmospheric processes occurring on Venus, Earth, and Mars. We learn that the greenhouse effect isn't all bad and is actually necessary for liquid water to exist on the surface of the Earth. We end our discussion with a brief introduction to human-caused climate change and the consequences of inaction. (Presented on May 2, 2021)
We are now done with the terrestrial planets and we can finally move to the outer solar system and "The Jovian Planets." This time we use Jupiter as a template to discuss the internal structures and atmospheres of each of these gas giants. Since they don't have surfaces for us to geologize, we instead turn our attention to the plethora of moons that encircle each planet. We end with a brief discussion on their ring systems. (Presented on May 9, 2021)
This is the last talk about our solar system! We finally catch up with all of the smaller things we've been sidestepping along the way, the "Asteroids, Comets, and Dwarf Planets!" After giving a brief history of those terms, we talk about the asteroids and comets in detail, covering both their physical properties and orbital properties. Then, we talk about the only dwarf planet we really know tons of information about, Pluto! Hopefully, I've illustrated just how much information New Horizons gave us when it flew by Pluto in 2015. We end by talking about impacts by asteroids and comets, including two relatively recent ones, both in Russia. (Presented on May 16, 2021)
Rounding up our large section on solar systems is all of the other "Exoplanets" in the Galaxy! The main problem with finding exoplanets is exactly that: finding them. There are three big methods that astronomers use and we talk about all three here and the biases inherent in these detection methods. We also compare the known exoplanets to the planets of our solar system and find that there are a wider variety of exoplanets than what we have in our solar system. Do we have to rethink our nebular theory of solar system formation? (Presented on May 23, 2021)
Now that we've ended our journey through the solar system, we're taking a quick break from astronomy to brush up on our relativity! In "Space and Time" we talk about how Einstein's Theory of Special Relativity says that all motion is relative, but that the speed of light in an absolute. We explore these concepts by using thought experiments, where, with two key assumptions, the results of time dilation, length contraction, and mass increase follow logically. (Presented on May 30, 2021)
Just as Einstein did after discovering special relativity, we will also generalize it to general relativity. In "Spacetime and Gravity" we leave the thought experiments behind and discuss the equivalence principle and the multidimensional nature of spacetime. Obviously this new view of the Universe has some profound effects on our understanding of it, and we see how general relativity leads naturally to the idea of black holes, gravitational time dilation, and redshift. But don't take my word for it, there are several easy-to-understand experiments that verify general relativity as well! We'll discuss them all. (Presented on June 6, 2021)
Now that we're done talking about the really big stuff à la relativity, let's move to the subatomic world and talk about "The Building Blocks of the Universe." Here, we give a brief introduction to the world of particle physics with its quarks, leptons, and bosons all wrapped up nicely in the Standard Model. Then we describe the two big laws of quantum mechanics: Heisenberg's Uncertainty Principle and Pauli's Exclusion Principle. But we're not just talking about this stuff for fun! There are astronomical implications to consider as well: stellar lifetimes, quantum tunneling, and black hole evaporation! (Presented on June 13, 2021)
To begin our broader discussion on stars, let's start by talking about the star we know the most about "Our Star, the Sun." We cover why the Sun shines and how its interior is organized into different zones. We take a journey to the core to see how hydrogen is fused into helium and then follow that energy outwards to talk about the solar cycle of sunspots and flares. Hopefully this will give everyone a good starting point to the terminology of stars! (Presented on June 20, 2021)
We started with the Sun, but the Sun is just one star. Let's talk about how astronomers "Survey[ing] the Stars." We answer three questions: how do we measure stellar brightness, how do we measure stellar temperature, and how do we measure stellar masses? Next, what happens when we arrange stars by their intrinsic brightness (their luminosity) and their temperature? We get an HR diagram and the stars arrange themselves into several groups. Finally, we end our discussion by talking about star clusters and how useful they are. The stuff in this talk will become very important for the coming weeks, so make sure you understand this stuff! (Presented on June 27, 2021)
Now that we've got some stellar basics out of the way, we're going to start a three-part mini-series on stars. The natural place to begin is "Star Birth!" Space isn't just an empty vacuum, there's gas and ust everywhere (to much annoyance). Some of that gas and dust is cold enough and dense enough for gravity to take over and collapse the entire gas cloud into a family of stars. We talk about how stars form, starting from gas clouds to protostars and on to true stars with their hydrogen-fusing cores. We also brielfy discuss the wide range of stellar masses we find in the Galaxy. Tune in next week for the remainder of a star's lifetime! (Presented on July 11, 2021)
What do stars do with the rest of their lives once they're formed? The answer ot that question is "Star Stuff!" Mass is not only an important property of a star, but it is also the most defining characteristic of a star. It determines how long the star will live and how it will evolve! Low-mass stars will only ever get hot enough to fuse hydrogen into elements like carbon and oxygen. Meanwhile, high-mass stars will fuse elements all the way up to iron. What happens after iron is quite explosive! (Presented on July 18, 2021)
Once stars are done fusing as many elements as they can, their bodies litter "The Stellar Graveyard." Stellar remnants come in three types. The low-mass stars will eventually shed their outer layers, leaving behind their exposed core as a white dwarf. Some stars will be so massive that instead of electrons, they'll leave behind a ball of neutrons known as a neutron star. And even more massive objects will skip all of that and end up as a black hole. All of these objects are weird in their own right and are the subject of many a science fiction novel. Learn the truth behind the fiction here! (Presented on August 1, 2021)
Now that we're done with stars, let's look at the giant groups of them known as galaxies. And what better place to start our galactic discussion than with "Our Galaxy, the Milky Way!" The Milky Way has a lot to offer us: an understanding of galactic structure; of galactic recycling, wherein stars scatter their enriched guts across the Galaxy, only to have those guts reformed in a new generation of stars; and galactic evolution, as we look at the differences between disk and halo stars. Finally, we see how nicely our observations match our theory as we briefly talk about minor galactic mergers. All of this information will be expanded upon and generalized when we talk about galaxies in general next week. Stay tuned! (Presented on August 8, 2021)
If we're going to talk about galaxies in general, we've got to talk about cosmology a bit too, so in "Galaxies and the Foundations of Modern Cosmology" that's exactly what we do! There are three broad categories of galaxies: ellipticals, spirals, and irregulars. Patterns exist between these broad types where ellipticals are generally more massive, brighter, and redder than the blue, star-forming spirals. Spirals also often exist in isolation or in small groups, whereas ellipticals exist in large groups and clusters of galaxies that number in the thousands. But to truly understand galaxies and their evolution, we need to introduce distance measurements to the furthest reaches of the Universe. We do so by talking about the Cosmic Distance Ladder, measurements of different objects that build and rely on each other. (Presented on August 15, 2021)
We can only understand "Galaxy Evolution by looking at snapshots of many different galaxies throughout the entire Universe. When we do hat, we get a basic model of galaxy formation. The growth of a galaxy might depend on its initial conditions, whether the protogalactic gas cloud was rotating or dense. It might also depend on galaxy mergers, where two (or more) galaxies crash into each other in a cosmic collision. After a galaxy has grown, it might go through a starburst phase, rapidly forming stars in just a few hundred million years, becoming incredibly luminous. Some galaxies are even active! Their supermassive black holes are spewing out radiation and shutting down star formation throughout the galaxy! Learn all that and more here. (Presented on August 22, 2021)
Now we're moving on to even bigger things that galaxies when we talk about "The Birth of the Universe." In the very early Universe, the conditions were radically different from the Universe we know of today. Matter and antimatter were spontaneously created and annihilated; the four forces that exist were likely combined into one "theory of everything"; and fusion happened not just in the cores of stars, but across the entire Universe! All that sounds nice, but what's the evidence? The two big pieces of evidence we have for the Big Bang are the cosmic microwave background and the abundance of helium in the Universe. Finally, we answer some outstanding questions from the previous talk, so you'll definitely want to check it out. (Presented on August 29, 2021)
We've talked about a lot of different objects in this series, but what would you say if I told you that everything we've talked about only makes up about 5% of the Universe? The rest of it is "Dark Matter, Dark Energy, and the Fate of the Universe." We spend most of the talk talking about the few things we know about dark matter: it flattens out the orbital speeds of stars in galaxies, it binds galaxies together in clusters, and it even supports large-scale structure formation throughout the Universe. What could it be, you ask? We don't really know. But despite all those unanswered questions, we know even less about dark energy. And that's a problem because the amount of dark energy in the Universe has a huge impact on the eventual fate of the Universe. Find out what that is here! (Presented on September 5, 2021)
An Astronomer's Perspective
No video!
To end this Astronomy 101 series, we take a stroll through "An Astronomer's Perspective" of the Universe. This talk is less about introducing new scientific ideas, and more about thinking back to everything we've talked about and putting it together. We wax poetic about the size of the Universe in both space and time. We tell the story of three amazing women who helped us understand the stars. And then you hear directly from me, what I think of when I look up at the night sky. There's no video for this talk, but you can read the talk in this blog post. Thanks for coming along for the ride. (Presented on September 12, 2021)
Ray Garner
Ray Garner
TAMU Astronomy Postdoctoral Researcher

I’m a scientist, Star Wars fan, and amateur photographer raised in Georgia. My research interests include galaxy evolution, star formation, satellite galaxies, and nebular diagnostics.