History of Astronomy Part 4: Kepler's Laws and Beyond

[@Astronomynatureandmusic]

I love the clear explanation supported by clear graphics - and the logical flow from one learning subject to another. Thank you!

[@bryan1377]

Kepler was ahead of his time. You know what these men would have contributed to this generation with all the equipment. It will blow their minds what we’ve also achieved

[@vedantsridhar8378]

They'd be like Stephen Hawking if they were born in the modern era.

[@thatoneguy611]

Kepler was well within his time. Someone had to lay the groundwork for us to go off of today.

[@quahntasy]

It's actually takes a genius to realize that the orbits are elipse and not circular.

[@isaacclark9825]

I suppose so. Kepler did it by using fairly simple geometry/trigonometry (with some insight of course) to actually trace out the orbit of Mars. Because Mars as a significant eccentricity, he was able to see quite directly that the shape he had plotted was not a circle.

[@Astronomynatureandmusic]

@@isaacclark9825 Your answer makes me wonder if you doubt the genius of that. Maybe it's also genius to discover something simple...

[@isaacclark9825]

@@Astronomynatureandmusic Did you notice that I wrote, "I suppose so?" Yes, electing to use simple, available math does not mean that he was not a genius.

[@richardpaulhall]

Genius and good data.

[@joystickwarrior7769]

To assume that a giant rock hurling at high speeds through an endless void then catching the gravitational pull only to revolve around it in a perfect circle every single time is actually rather foolish.. It's kind of common sense, he just had to have an equation behind it and give the orbit a name.

[@insouciantFox]

I know I am a bit biased being a Astrophysics major, but Kepler's Laws are my favorite laws in science.

[@kasparhauser4472]

Well, being in Corona lockdown for weeks, I will never say "only house arrest" again...

[@biitizen_bela]

LMAOOOO but ify hard

[@lazyindiandude]

Hey! Thanks for this! Now I can revise these laws quickly and easily! 😁

[@naimulhaq9626]

Kepler, Copernicus, Galileo, Leibniz, Newton, Euler etc., were blessed with 400,000 books in the library of Alhambra, Andalusia, when the Moors left Spain. The books were translated by Europeans and helped them develop science, mathematics, medicine etc., and freed them from the dark ages and into enlightenment.

[@NoName-fc3xe]

Citation please

[@Prometheus7272]

No Name Don’t expect a reply from him anytime soon

[@richardpaulhall]

@@NoName-fc3xe Just do a Google search. The need to know ht direction to Mecca was important to the Muslims and they developed spherical geometry to do just that.

[@DG-sn2js]

@@richardpaulhall The first Mecca was not in Saudi. Possibly in Jordan (Petra) or in Euro Asia. Read Dan Gibson documentaries!

[@AthariTaamari]

@@DG-sn2js yea read a random guy's documentary on Mecca, lol

[@isaacclark9825]

The constant of proportionality between P^2 and a^3 actually depends primarily on the mass of the sun and not the mass of the planets. It actually depends on the sum of the mass of the planet and sun, but the planets masses are all a small fraction of the mass of the sun.

[@aidanjohnwalsh2129]

I did not follow the bit about Mass but the apparent speed of a planet's movement through the sky is much clearer.

[@jgtbym601]

I have a rudimentary question: If the Sun represents a focal point in an elliptical orbit of a planet in our solar system, what is actually at the other focal point? There is no physical celestial body that we can visually observe. Does it have something to do with how the conditions are balanced in the "fabric" of time-space dimension?

[@ProfessorDaveExplains]

correct, no physical object at the other focus! it's just the way the gravity works out, the system is too complicated for everything to end up perfectly circular, the planets tug back just a tiny bit on the sun

[@charlieangkor8649]

That depends on the distance between the two focal points. If the distance is less than the radius of the Sun, then there's Sun in the other focal point. If it's more, then there's empty space. If another planet happens to pass thruogh the other focal point, then there's a planet. If an asteroid happens to pass through the other focal point, then there's an asteroid. If an Oh-My-God particle happens to pass through the other focal point, then ther's an Oh-My-God particle. If a neutrino happens to be passing through the other focal point, then there's a neutrino. If a neutrino happens to pass through the other focal point and another planet happens to pass through that other focal point at the same time as well, then there's a neutrino inside a planet. There are numerous possibilities.

[@Delibro]

To hear an American talk about a person (Kepler) born only 20 minutes drive from my home is strangely satisfying :D

[@eljison]

Another great series of videos. NOTE: if you look up the pronunciation of aphelion, 90% of the time you will get "uh-FEE-lee-un". However, 90% of astronomers pronounce it as "AP - he -lee- on ". This is closer to the classic Greek pronunciation (not modern Greek) and we prefer this pronunciation because we are contrasting the roots of the words - ap-helion vs peri-helion, as in peri-gee vs. apo-gee, geo-centric vs. helio-centric, etc. Probably, the best argument for pronouncing it as AP-helion, with "p" sound, is that the Flat-Earther David Weiss pronounces it with the "f" sound. 🙂

[@rheiagreenland4714]

The -helion suffix is derived for the Greek word/god for the sun though. Ap- is just tacked on as a prefix. P and H being adjacent is purely coincidental and has nothing to do with the 'f' sound represented by ph

[@rajbhai-tp7cf]

Just like upholstery. You wouldn't pronounce it you-folstery.

[@Bahraini0]

محتواك شيق وتقديمك رائع ❤

[@tom2443]

Wow excellent tutorials. Great work as always Dave ☺️

[@RabbitHorse777]

Galileo supposedly whispered, "and yet it moves" [the Earth around the sun] at the moment he recanted his heliocentric theory. Maybe true, maybe not.

[@josephsant624]

Most likely not true. First mention of the story was more than a century after Galileo's death by a man that was neither a scientist or historian and not known for his veracity.

[@derrickmcleod]

Hey Professor Dave, what happened to videos 20-31? Their all Private. How can we view them?

[@ProfessorDaveExplains]

i'm releasing them weekly, don't worry you'll get them all!

[@derrickmcleod]

@@ProfessorDaveExplains Thank you, you make the best content. Keep up the great work.

[@aidanjohnwalsh2129]

Professor Dave, please do your thing with the amazing graphics on how an astrolabe works. Resources are scant and difficult to comprehend. The one I made is basically a desk ornament.

[@ahmedhabashy3190]

Thanks

[@m.zakriam.zakria5627]

Great effort

[@kennkong61]

4:13 The mass of an orbiting body is not a factor in the period of the orbit *around the sun*. A Trojan asteroid has the same period as Jupiter, for example. The mass of another central object matters, as in the earth/moon system, but in the orbits of the planets, the mass of the sun is a common constant.

[@charlieangkor8649]

He's a professor and he says this. What a shame.

[@carultch]

@@charlieangkor8649 He is technically correct, but misleading. The mass of the planet is mostly insignificant. In binary circular orbit where both masses are significant, it depends on the sum of the two masses.

[@aidanjohnwalsh2129]

I will have to watch the Newton videos but my limited guess at what was meant is that a smaller mass might mean a greater speed at the same orbital distance... total thumb suck but I'm fascinated.

[@isaacclark9825]

@@aidanjohnwalsh2129 Perhaps, but if that is what was meant, then it is incorrect. The mass of that planet has only a small effect, but it is the opposite of what you describe,

[@carultch]

@@aidanjohnwalsh2129 Think of it like the mass of a falling body or the mass of a swinging pendulum. Due to the fact that participation in the force of gravity, and the inertial property of matter come as a package deal, these two factors "cancel out" of the equation. As long as the mass of the source of gravity for these experiments, is substantially greater that the impact on its motion, from the Newton's third law reaction forces due to these experiments is negligible. The same is the case for orbit, where the central orbited body is significantly greater than the orbiting body. The gravitational force per unit mass is the same, at any given orbital position. This is why as mentioned previously, Jupiter's Trojan asteroids orbit at the same period as Jupiter itself. The solar system is a good example, where the central body (sun) has over 99% the mass of everything in it, thus making every example one where the mass of the planet/comet/asteroid/etc is insignificant. The sun indeed does move due to these orbits, but not by much relative to the scale or the orbit, called solar wobble. It's the same order of magnitude as the sun's own diameter. Binary stars wouldn't be such an example, when both stars are of significant mass. Similarly, planet-moon systems like Pluto/Charon, or to some extent, the Earth and its Moon, are examples where you need to consider the two way street of gravity.

[@ehatipo4598]

Here I am again to listen to my lectures. I haven't understood anything from my prof as usual and show up here.

[@PunmasterSTP]

Kepler’s Laws? More like “Cool knowledge for ya!” Thanks again Professor Dave.

[@skullskill6086]

Do you have any idea how awesome you are??!! Thanks for all this amazing flow of understanding.. truly grateful to you.. thank you! :) :) :)

[@samk6042]

Awesome

[@glaucosaraiva363]

Kepler discovered his laws by observation. However, what is the reason for the orbits to be elliptical? Is it because the sun is in motion and so the center can not be unique?

[@ProfessorDaveExplains]

i think that's just how celestial dynamics works! things orbit around the center of mass of the system, and that's what produces elliptical motion. but i'm no mathematician so i may not be understanding it correctly.

[@glaucosaraiva363]

Thx

[@schifoso]

Newton showed that a body moving towards something like the sun could orbit the sun in a conic section. The planet could move toward the sun and slingshot outwards (like a hyperbola or parabola), which is an open ended conic section. The planet could move toward the sun and go into a periodic orbit that is elliptical (closed ended conic section). Depending on how the body approaches the sun (velocity), and a little bit of dependence on other possible external forces, the type of orbit is determined. To much velocity, and the orbit is a open ended conic section. To little velocity, and the body could spiral or go directly into the sun. Just about the right velocity and the body would whip around the sun and then be pulled back towards the sun (close ended conic section) into a periodic orbit. Depending on the initial velocity, eccentricity of the elliptical orbit is determined. That eccentricity could be zero, creating a circular (another type of conic section) orbit, if all the variables needed to get the body into a periodic orbit were exactly right. That has a low probability, so eccentric elliptical orbits are most common. So to much velocity equals open ended orbit because there isn't enough gravity for the sun to pull the body back towards it after the body has been slung away. Just right velocity allows the sun to pull the body back towards it when after it's been slung away.

[@ytnoname1189]

As everything in physics... the answer again, somehow is gravity.

[@charlieangkor8649]

No. You need to throw the planet precisely in order for it to fly in a nice round circle. If you just throw it carelessly, it is going to fly around the Sun in an ellipse. Even if the Sun was nailed down to the space, it would be still the same.

[@eljison]

Kepler's 3rd Law states that the cube of the semimajor axis is EQUAL to the square of the orbital period when the semimajor axis is in AU and the orbital period is in years. It does NOT depend on the mass of the planet. Newton later expanded on Kepler's laws and in his more general version any two objects have this in proportion and the mass of the planets must be included. When using Newton's version of Kepler's Laws we use standard units (depending on which unit system is used).

[@SakariEklund]

in about 2:27, do you mean that planets' distance's of perihelion and aphelion stay the same, i.e their ratio is a constant? You say that the distances are similar for the planets but that can't be true? If they were the same, they would be in the same distance from the Sun. Am I missing something? Thank you

[@rporta]

incredible what Kepler, Galileo, and Copernicus did

[@jondeere5638]

Kepler was not Brahe's assistant. He had to beg for a position under Brahe who refused to let him see the data. When Brahe died his relatives inherited the data, which they refuse to give to Kepler. So he stole it.

[@abdifatahbudul8467]

Still can't believe how this sceintists was so genius and educated💥

[@aidanbramley3964]

This man low-key carrying me through 6 form

[@tvjacket9245]

fr

[@Indoor0gamer]

Do you have a course for an 8 year old homeschooled student?

[@fallendown8828]

I give all my respect to those who helped science but it is still not enough! I must do something and write Gallileo or Kepler under it because they did something so amazing that no other figure in human history can do, they added non-Eartg objects to our understandings. They are heros... no. They are SCIENTISTS!

[@mayankverma4271]

Hi Professor, Can u please tell me that which software you are using to make this type video

[@ProfessorDaveExplains]

adobe after effects

[@mayankverma4271]

@@ProfessorDaveExplains too much thanks to your prompt reply. One more thing I want to know that how much time and money will need in setup. Your video are amazing.

[@ProfessorDaveExplains]

you can learn the basics in a week or so, i'm not sure what adobe suite costs nowadays but it can't be all that much

[@craigbarkle1441]

Elliptical orbits results in exactly equivalent time intervals because the Earth spins at different rates. The distance travelled also varies relative to the conservation of momentum. The 24 hour day is the same at all points in the orbit path. 😎🧠🤘

[@jondeere5638]

It makes you wonder really, how many people actually understand that a perfect circle orbit embodies the principle of equal areas swept by equal time? Not an ellipse but a circle. The mystery is that 'why does an elipitcal orbit behave as if it's a circular orbit'? And that all those graphical pictures of the ellipse sweeping equal areas over equal time are extreme exaggerations of Kepler's law to make it more comprehensible. The elliptical orbit that Kepler measured was very slight, only a few degrees off the norm. This leads to the idea that the greater the elliptical orbit the less chance there is of a planet maintaining an orbit. I once wrote to Freeman Dyson and asked 'would gravity increase or decrease as a function of the rotational speed about the sun'? I never received a reply.

[@DemiHalf]

Welcome back, Galileo.

[@marcusanthony9322]

I don't get these religious types, nothing in the bible says that the earth is flat or the center on the solar system.

[@ronancruz5428]

who else is here cause of school???

[@sonicdoesfrontflips]

Humanity: *gets smarter* Catholic church: "I'm gonna stop you right there"

[@ghosthawk10]

I know im late, but how did gallileo observe spots on the sun. Would he not be blind using a telescope?

[@carultch]

He used his telescope to project the image on the sun onto a white sheet of paper, and looked indirectly at the sun through the projection onto the paper. He did eventually go blind in 1638 at the age of 72, but the cause was unrelated to his work with observing the sun.

[@burtReynolds3]

Fuck, I love these videos

[@astrospacetech2827]

You got ads on my view👍

[@Sam_Sam2]

What sources did use for this video. Not trying to sound like a flat earthed?

[@ProfessorDaveExplains]

An astronomy textbook.

[@mekore]

it is a sin not to retrace these...

[@mind-h4i]

Tycho brahe The intelligent lunatic

[@xmvziron]

I believe aphelion is pronounce like ap-helion.

[@aidanjohnwalsh2129]

... and foci like fow-kai.

[@spectrumofscience]

I just posted Laws from a book

[@matogrosso555]

👍

[@micnorton9487]

💯💯🖖

[@deepakk1347]

Hey

[@jerometaperman7102]

Fortunately for us and for everyone, Newton was born in a place not dominated by the catholic church. We are still living with these attitudes today with people insisting that their creation myths be given equal footing to science in the classroom. Similar is the political pressure to deny global warming and even the presence of a pestilence that killed millions of people in only a couple of years. Will we, as a species, ever learn to trust the scientific method more than books from millennia ago?

[@betaorionis2164]

The Protestant church was by no means more sympathetic to scientific progress, in the 16th century, see the case of Miguel Servet. BTW, the Catholic Church acknowledges evolution and the Big Bang. Jesuits have produced scientists for centuries. Pope Francis was extremely vocal in favour of COVID vaccination. The Vatican manages several telescopes around the planet (Google for Vatican Advanced Technology Telescope). I have the impression you may have mistaken some US “so-called “Christians” for the Catholic Church.

[@feynstein1004]

I used to think like that too but I've recently gained a new perspective on this. The reason people are so adamant about religion is because............well, it's a uniquely human trait and...... they're just being human. This tendency to pass on non-genetic information to the next generation, without understanding it, without thinking about it, without questioning it, simply because either a) your parents passed it on to you or b) you learned it during your lifetime, is what allowed us to become the dominant species we are today. Think of our hominin ancestors 2 million years ago. Did they understand what they were doing? Or that using tools would give them an evolutionary edge over other species? Probably not. They just had the genetic inclination to a) try new things and b) when a significant new thing was discovered, pass it on to the next generation without question. It's pretty much a new form of life, building upon existing life forms (humans). But whereas biological life can only ensure the continuity of genetic information, this new life form (let's call it memetic, from memes, as Richard Dawkins originally coined, and used, the term), ensures the continuity of non-genetic information. If not for this tendency, we'd have no form of technology, including language. Memetic life functions quite similarly to genetic life too, which isn't surprising, since it did emerge from genetic life. Just as with genetic life, most of the information (memes) in any given generation gets passed down to the next generation, and then to the next, and so on. But just as with biological life, this copying process isn't perfect. Mutations occur, and sometimes new information finds its way into the meme pool (the analog to the gene pool) and then gets passed on. The key difference being that memetic life evolves much faster than genetic life. Another interesting analogy is that with genetic life, most of the DNA is useless and doesn't really do anything (junk DNA). Similarly, most of the information that gets passed down is useless. This is not necessarily a bad thing though, since the useful stuff gets passed along too. Religion is just a byproduct of this and falls under the junk meme category. However, much as junk DNA is still part of an organism's genome and any attempt to change it would be met with hostility and resistance by the organism, religion too is part of people's menome and any attempt to change it will be met with hostility and resistance. There's also the added complexity that psychologically speaking, the human brain isn't a single entity but a partnership between two entities: the unconscious brain and the conscious brain, with the former being the more powerful partner. More often than not, the unconscious brain makes a decision and the conscious brain simply finds a way to rationalize it. That's why it's impossible to reason people out of religion. The unconscious part of their brain has already made the decision to not let go. No matter how much you try to appeal to the conscious (and rational) part of their brain, it is powerless against its partner. Not that I'm implying atheists are better. Their unconscious brains are simply wired differently and aren't as resistant to change. In terms of weights and biases, their brains give more weightage to logic/reason than to memetic continuity. We're all just pawns of evolution, doing what we're programmed to do. And atheists judging religious people for not being reasonable is like a bird judging a fish for not being able to fly and vice versa (quote from Einstein). It's.... not really the fish's fault, or the bird's. One last thing - in terms of memetic life, Christianity is analogous to a virus that destroys other memes and replaces them with copies of itself. The host doesn't realize it's been infected, and depending on its genetic/memetic predisposition, tries as much as possible to further spread the infection. The closest biological analog would be the rabies virus (forgive me for how incredibly dehumanizing that sounds but again, it's not really the dog's fault) Sorry for the giant wall of text 😅

[@jerometaperman7102]

@@feynstein1004 - I would like to argue that we have a great deal more control over our junk memology than our junk DNA. We have more power to identify and eliminate it, if we choose. If we don't eliminate it, we do ourselves harm as a society and as a species by allowing mysticism an equal footing with hard science. There have been thriving societies in the past that lost their leadership position due to the mystics gaining too much influence. The arab world used to be the center of learning, culture, and the discovery of knowledge. Then certain people got into power who decided that science and math was ungodly. Today, we have people openly calling for government to be based and controlled by the Christian faith. No good will come from that.

[@seriusxs957]

part 5 when? I really wanna get to einstein

[@ProfessorDaveExplains]

Einstein is covered in the modern physics series, he was a physicist, not an astronomer.

[@seriusxs957]

@@ProfessorDaveExplains oh ok thanks, did not realize there was a difference

[@babucarrnyass414]

Keplers law

[@maxqueue5211]

iirc kepler stole the data from brahe.

[@omaro7015]

Ibn Al-Shatir claimed the sun was in the center and wrote his works 150 years before Copernicus, but ok.

[@ProfessorDaveExplains]

There were heliocentric models in Ancient Greece too. It doesn’t matter. They weren’t empirical.

[@DuelScreen]

The Catholic Church gets a lot of flack for what they did to these early scientists but Christianity contributed positively to the development of modern science as well. Where did the notion that the universe could be understood come from? It didn't come from Greek Mythology with its panoply of fickle gods. Rather, it came from the christian notion of God as a single benevolent and all-powerful Being. The world was knowable because God made it that way and humans are able to infer God's attributes by studying the universe. Put another way, there are reasons why most of the early scientists were all christians. It was the christian worldview that helped birth modern science as we know it today.

[@PoonsYungv]

Sir isaac newton must’ve been Galileo’s reincarnation

[@daffavirwandy7694]

Damn the past where hell. But mathematical formula is fucking easy. Just using basic math and naked eye observation. NOW MODERN PHYSICS? IT USE MONEH