The Interlocked History of Gravity, Astronomy, and Light

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This is the second lecture series of my complete online introductory undergraduate college course. This video series was used at William Paterson University and CUNY Hunter in online classes as well as to supplement in-person course material.
00:00:00 - lecture 1: Cosmic Distances using Parallax
00:17:49 - lecture 2: How do we know that the Earth is Round?
00:27:03 - lecture 3: How Big are the Sun and Moon?
00:36:23 - lecture 4: How Did Geocentrism Fail the Tests of Science?
00:54:14 - lecture 5: The Dawning of Astrophysics
01:16:20 - lecture 6: Galileo, the Father of Science
01:43:21 - lecture 7: Galileo's Legacy
01:56:01 - lecture 8: Newton's Laws, Orbits and Gravity
02:20:56 - lecture 9: A Safe Intro to Physics Equations
02:50:15 - lecture 10: "And Yet It Moves": Galileo Vindicated
03:08:28 - lecture 11: Wave Motions Everywhere
03:27:12 - lecture 12: The History of the Theory of Light
03:38:47 - lecture 13: Newton's Corpuscular Theory of Light: So Close, but So Far
03:51:44 - lecture 14: The End of Newton's Theory of Light
In this lecture set, I set the stage with a discussion about finding distances to stars using parallax. To get those distances, we need to learn about the nature of the Earth being a sphere. Then, we follow Aristarchus of Samos as he discovers the sizes and relative distances of the Earth, Moon, and Sun. Armed with that, we can address why geocentrism held sway for nearly 2000 years and why it was overthrown. Then, I discuss the accomplishments of Nicolas Copernicus, Tycho Brahe, and Johannes Kepler in the advancement of science. We talk about the transition to a heliocentric model, and how the groundwork was laid for it to be supported eventually by Newton. Then, I move on to the accomplishments (and failures) of Galileo Galilei, the Father of Modern Science. Next, we see the effect of Galileo's work around him and the work that surrounded him. Jeremiah Horrox predicted and observed a transit of Venus, the book Galileo should have written was finally done, the Geocentric model held its head up for one more fight, and the Leaning Tower of Pisa legend was born. This leads us to Newton's Laws of Motion and his Law of Gravity. We also talk about centers of mass and other things related to the understanding of orbits. They provide a framework for predicting the motions of the planets around the Sun. And how everything moves. Next, we take a diversion into the nature of mathematics. I find that a lot of people have a fear of math. I make it a point in my classes to overcome that fear if possible. After that, we discuss exactly how we know the Earth moves. We learn about parallax and stellar aberration. Finally, we can say for certain that the Earth moves, even though we don't feel it. Thus science gives us one of the first answers that goes against "common sense," but is nonetheless true. Following this, it's another chalk-and-talk, where I describe what wave motion is and how it applies to water, sound, and light. Then, we begin the discussion of the origin of our current understanding of the nature of light. We learn about the progress of both the particle and wave explanations of light through history. The penultimate lecture leads us to Newton's contribution to the understanding of light. We learn about his corpuscles and how they are not waves. As we traverse the history of light and understand how it grows with time, we see how great minds tried to wrestle with big ideas as the ideas arose and the experiments that supported them became possible. We see their missteps and we learn from them. We also see how the science endeavor is a truly human one, with all our foibles and strengths on display. Finally, we see how the theory of light advances. Young's double-slit experiment and Fresnel's investigation of diffraction put the nail into Newton's corpuscles. The solidification of the wave theory of light, however, will circle around to bite the world in the backside.

[@jacobbott9825]

Let’s go! I love you

[@abhishekkumargautam4710]

does light has mass if not then how it is able to get momentum and we studied that it travels in a straight path but it does not it travels in a curved path. If possible please answer

[@bojanperko]

If I understand correctly as a lowest-tier amateur, light is actually always taking a straight, shortest path from its point of view, it's just that the space itself isn't straight and going straight actually turns out to be making a turn around whatever is causing the curve in space to be there. This is just a guess, might be entirely wrong.

[@JasonKendallAstronomer]

Good call! However, when we say that space is curved, it still means that there is a shortest path. And that path in the curved space is "straight". Something traveling straight in a curved space won't "know" that it's, moment by moment, in a curved space. Every spacetime can be looked at as locally Minkowski (i.e. flat), depending on what "local" is. But curvature can be measured by traveling in loops, or comparing adjacent paths.

[@DrDeuteron]

Momentum is total energy/c^2 times velocity, so massless particles carry the maximum possible momentum per unit energy.

[@fjs2456]

Thx

[@swenic]

How does the suns orbit /"wobble" around a central point of gravity affect distance measurements using parallax?

[@JasonKendallAstronomer]

A lot. When taking into account microarcsecond parallaxes, such as ESA's HIPPARCOS and Gaia mission did, then this must be included into the expected periodic "wobbles" that will be present in unfiltered data sets. They spent a LOT of time removing those, and many other, bumps in the data.

[@lafenelson3212]

The sun wobbles about an area roughly equal to its radius, changing the base of the parallax right triangle by ~0.5%. Earth's aphelion/perihelion need to be accounted for as well.

[@extec101]

see a pic of isac newton and he is almost the exact same looking like richard hammond but one invented a law of physics and the other one try to brake it.

[@CliffSedge-nu5fv]

There is an embarrassing mistake at 2:06:20 - That is not an action-reaction pair. There are two separate action-reaction pairs: Earth pulls ball down with gravity, ball pulls Earth up with gravity. Ball pushes down on table with normal force, table pushes up on ball with normal force. Action-reaction is not what is keeping the ball in equilibrium. The ball is in equilibrium because of balanced external forces from two different objects.

[@JasonKendallAstronomer]

Thanks for the note. I’ll be redoing this series as well soon. It needs a full redo.

[@jaswik2023]

@@JasonKendallAstronomer should I wait for you to redo it or should I watch this anyway and watch the redo as well, Im a complete beginner

[@JasonKendallAstronomer]

I'd just watch this now. Re-doing this one is not at the top of my list. There are not a lot of mistakes, and the content is good. It's just the quality isn't top-notch.