The Rickroll Is Basically All Scientists In A Nutshell

My favorite YouTube video as of now (I know this doesn’t seem like it’s related to space - but it has a nice discussion about black holes and hawking radiation, which is I love it so much)

Remember kids: be cautious of bouncy castles!

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That’s how I want the world to end

better than us all getting killed by a pandemic or a nuke

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On November 12, 1833, there was such an intense meteor shower that it was possible to see up to 100,000 meteors crossing the sky every hour. At the time, many thought it was the end of the world, so much that inspired this wood engraving by Adolf Vollmy.

It’s easy to forget that thousands of comets, asteroids, and meteors are near us everyday. They seem like such a rarity.

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Cosmonaut Ivan Vagner obtained this image of the comet NEOWISE a few hours ago from the International Space Station. He says that the dust tail looks very good from there. It is worth enlarging the image.

via reddit

Omg xD

It’s true though. Do you believe in a flat Earth? Look up at the moon. See that curvature? If the Earth were flat it’d just be a straight line, running across the moon.

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what you think? is this post right?

I mean, that is true. Atoms would really like communism (aside from Noble gases, of course).

Fluorine be like SHARING IS CARING

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Hydrogen bond vibes

In a sense cosmology contains all subjects because it is the story of everything, including biology, psychology and human history.

Peter Theodore Landsberg

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THE LIFE OF A STAR: CLASSIFICATION

In order to understand the life of a star, we must understand star classification.

        And there are SO many different ways to classify a star.

        In star classification, understanding the relationship between color and temperature is crucial. The greater the temperature of the star, the bluer they are (at their hottest, around 50,000 degrees Celcius), while red stars are cooler (at their coolest, around 3,000 degrees Celcius). This occurs on a wide range (fun fact: stars only come in red, orange, yellow, white, and blue, because stars are approximately something called a "black body"). For example, our Sun is a yellow star with a surface temperature of 5,500 degrees Celcius (The Life of a Star).

        But why is this so? In order to understand that, I'm going to tell you about how stars live at all. This is what will determine the entire life of a star - something we'll be focusing on throughout this series. Two words: nuclear fusion.

        Nuclear fusion is "a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifested as either the release or absorption of energy." (Wikipedia) And this is where nuclear fusion gets REALLY important to stars. Throughout their lives, stars undergo nuclear fusion in their core. This is mostly in the form of fusing two or more hydrogen atoms into one or more helium atoms. This releases energy in the form of light (the pressure of nuclear fusion in the core also prevents the star from collapsing under the weight of gravity, something we'll get to later). The energy transports to the surface of the star and then radiates at an "effective temperature." (Britannica) 

        Stars are different colors due to differing amounts of energy. This is best explained by Einstein's e=mc2 or the mass-energy equivalence. In other words, the more mass something has, the more energy, and vice versa. Stars with greater mass undergo more nuclear fusion - and as such - emit more energy/temperature. And so, the bigger the star, the greater the temperature, the bluer the star; and the smaller the star, the lower the temperature, the redder the star (Universe Today). Another way to think about this is this: the hotter something is, the shorter frequency of energy it emits. Blue light has a shorter frequency than red light, and so, higher energy/temperature stars are bluer.

        Another important classification of a star is its luminosity (or the brightness, or the magnitude of the star). (The Life of a Star)

        The most famous diagram classifying stars is the Herzsprung Russell Diagram, shown in this article's picture. The x-axis of the diagram shows surface temperature, hottest left, and coolest right. The y-axis shows brightness, brighter higher, and dimmer lower. There are main groups on the diagram. 

        Most stars fall in a long band stretching diagonally, starting in the upper left corner and ending in the right lower corner, this is called the main sequence. The main sequence shows stars which mostly use their life going through nuclear fusion. This process takes up most of a star's life. Most stars which are hotter and more luminous fall in the upper left corner of the main sequence and are blue in color. Most stars that have lower-masses are cooler, and redder falls in the lower right. Yellow stars like our Sun fall in the middle. 

         The group located in the lower-left corner are smaller, fainter, and bluer (hotter) and are called White Dwarfs. These stars are a result of a star like our Sun one day running out of Hydrogen.

          The group located right above the righter's main sequence is larger, cooler, brighter, and a more orange-red or red, are called Red Giants. They are also part of the dying process of a star like our sun. Above them in the upper right corner are Red Super Giants, massive, bright, cooler, and much more luminous. To the left of the Red Super Giants are similar stars which are just hotter and bluer and are called the Blue Super Giants.

        That explains the most famous star classifying diagram. The important thing to remember is the data on the chart is not what a star will be like it's whole life. A star's position on the chart will change like our Sun will one day do.

        In a ThoughtCo. article on the Hertzsprung Russell Diagram, Carolyn Collins Petersen wrote: "One thing to keep in mind is that the H-R diagram is not an evolutionary chart. At its heart, the diagram is simply a chart of stellar characteristics at a given time in their lives (and when we observed them). It can show us what stellar type a star can become, but it doesn't necessarily predict the changes in a star." ( The Hertzsprung-Russell Diagram and the Lives of Stars)

        And this will continue to be important in the next chapters. Stars don't just stay in the same position their entire lives: they change in their color, luminosity, and temperature. In this series, we'll be tracking how stars form, live and die - all dependent on these three factors - and nuclear fusion - again - super important :)

Previous -  Chapter 1: An Introduction

Next -  Chapter 3: Star Nurseries

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THE LIFE OF A STAR: STAR NURSERIES

How did this "star stuff" come to exist? The life of stars is a cycle: a star's birth came from a star's death. When it comes to star birth, the star nebulae reigns supreme.

        A Nebula (take a look at pictures, they're some of the most beautiful things in the universe) is a giant cloud of dust and gas. This is the region where new stars are formed. Nebulae live in the space in between stars and between galaxies - called interstellar space (or the interstellar medium) - and are often formed by dying stars and supernovas (NASA). 

        This cloud of particles and gases is mostly made of hydrogen (remember - stars mostly fuse hydrogen!). These appear as patches of light (emission, reflection, or planetary-types) or a dark region against a brighter background (dark-type). This depends on whether "... it reflects light from nearby stars, emits its own light, or re-emits ultraviolet radiation from nearby stars as visible light. If it absorbs light, the nebula appears as a dark patch ..." (The Free Dictionary). 

        There are four main types of nebulae: emission, reflection, dark, and planetary nebulae.

        Emission nebulae are a high-temperature gathering of particles, of which are energized by a nearby ultra-violent-light-emitting star. These particles release radiation as they fall to lower energy states (for more information on electrons moving to energized states and falling back to lower states, read this). This radiation is red because the spectra/wavelength of photons emitted by hydrogen happens to be shifted to the red-end of the visible light spectrum. There are more particles than hydrogen in the nebulae, but hydrogen is the most abundant.

        Next up is the reflection nebulae - which reflect the light of nearby stars. As opposed to emission nebulae, reflection are blue, because "the size of the dust grains causes blue light to be reflected more efficiently than red light, so these reflection nebulae frequently appear blue in color ...." The Reddening Law of Nebula describes that the interstellar dust which forms nebulae affects shorter wavelength light more than longer-wavelengths (CalTech).

        Then there's the "emo" nebulae: dark nebulae. These are, very simply, nebulae which block light from any nearby sources. The lack of light can cause dark nebulae to be very cold and dark (hence their name), and the heat needed for star formation comes in the form of cosmic rays and gravitational energy as dust gathers. Many stars near dark nebulae emit high levels of infrared light (this type is much more intricate then I've explained, but that summary will do for now. If you're interested in learning more, read this).

        Finally, there are planetary nebulae. And these aren't nebulae made of planets. These nebulae are formed when stars (near the ends of their life) throw out a shell of dust. The result is a small, spherical shape, which looks like a planet (hence their name) (METU).

        Nebulae themselves are essentially formed by gas and dust particles clumping together by the attractive force of gravity. The clumps increase in density until they form areas where the density is great enough to form massive stars. These massive stars emit ultraviolet radiation, which ionizes surrounding gas and causes photon emissions, allowing us to see nebulae (like we discussed in the types of nebulae). Universe Today said, "Even though the interstellar gas is very dispersed, the amount of matter adds up over the vast distances between the stars. And eventually, and with enough gravitational attraction between clouds, this matter can coalesce and collapse to forms stars and planetary systems."

        Britannica notes the structure of nebulae in terms of density and chemical composition: "Various regions exhibit an enormous range of densities and temperatures. Within the Galaxy’s spiral arms about half the mass of the interstellar medium is concentrated in molecular clouds, in which hydrogen occurs in molecular form (H2) and temperatures are as low as 10 kelvins (K). These clouds are inconspicuous optically and are detected principally by their carbon monoxide (CO) emissions in the millimeter wavelength range. Their densities in the regions studied by CO emissions are typically 1,000 H2 molecules per cubic cm. At the other extreme is the gas between the clouds, with a temperature of 10 million K and a density of only 0.001 H+ ion per cubic cm." The composition of nebulae also aligns with what we see with the rest of the universe, mostly being made of hydrogen and the rest being other particles, particularly helium (this matches up with the composition of stars!).

        Fun-fact: supernova can create nebulae, but also destroy them. Possibly the most famous nebulae, the "Pillars of Creation," the Eagle Nebula, is hypothesized to have been destroyed by the shockwave of a supernova 6,000 years ago. Since it takes light 7,000 years to travel from that nebulae to the Earth, we won't know for another 1,000 years (Spitzer). If you're wondering how exactly we could know how far nebulae are, check out this article about a new way to measure that distance using the "surface brightness-radius relation", and other distance measurements (such as the parallax measurement).

        Now, why did I just explain the intricacies of nebulae in 900 words when this series is supposed to be about stars? Well, when we talk about the birth of a star (and the death sometimes, too), nebulae become important. Take note of what we've discussed in this article: formation, chemical composition, and density. It'll be important in our next chapter (and nuclear fusion, but when is that not important?).

First -  Chapter 1: An Introduction

Previous -  Chapter 2: Classification

Next -  Chapter 4: A Star is Born

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Omg that’s hilarious xD

Cuz the way the second equation is written assumes that the c^2 in the mass-energy equivalence equation is actually the c^2 from the Pythagorean Theorem when it’s actually just the speed of light (squared, since c IS the speed of light).

I do love the Pythagorean Theorem though, even though (don’t come after me) I prefer the version where you take the square root of both sides so it’s c = sqrt(a^2 + b^2). It’s just easier!

Nerd rant, over.

(Also, can you imagine Einstein, Hawking, and Neil being friends!? It’s like my dream come true)

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Genius?

I’m re-watching Crash Course: Astronomy for about the 10 x 10^23 time

Want to join me?

It’s one of my favorites :)

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