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Blast it Tom!

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Sounds like fun! To complete this little sidebar, years ago I had the quintessntial egghead college physics professor for my freashman physics class: bald, glasses, a paunch, tweed jacket and bowtie. You NEVER missed his class, and I am sure now that was why he did what he did; that is, every time he did a demonstration he comically fouled something up. He jolted himself with the Jacob's ladder, he was colorblind and his assistant had to keep correcting him on the colors of the cars in the elastic collision demonstration; he had a large pendulum suspended from the ceiling like a wrecking ball and it swung at least 15 ft each way; he released it right next to his head and after a couple of swings noted "Now see how I can..." but he had put his arm up next to his head, pointing preacher-style and the pendulum impact sent his hand into his head and his glasses sailing across the room!

He was an associate of David Halliday and Robert Resnick (who'd written the book); one day he had Dr. Resnick lecture us. We were starstruck.
 

Grog6

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I was lucky enough in my career in PET tomography to get classes in radiation detectors to get taught bu Dennis Persik and Glenn Knoll.
They were truly giants in their field.
I'm an expert in PMT detector design; few people use vacuum tubes anymore, so it's a dying art.
 

Funkworks

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The Earth not only rotates, but
  • over 41 000 years, its axis of rotation oscillates between 22.1 and 24.5 degrees, and
  • over 26 000 years, its axis of rotation precesses (wobbles) a full circle (base of a cone).
If anyone knows where I can find a desk globe displaying this (like a gyroscope with an Earth model as a rotor), I want one. Why? Because for too long I was mislead by regular globes into thinking the axis of rotation was fixed in space and it irks me.
 

Antares JS

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If anyone knows where I can find a desk globe displaying this (like a gyroscope with an Earth model as a rotor), I want one. Why? Because for too long I was mislead by regular globes into thinking the axis of rotation was fixed in space and it irks me.
A lot of desk globes have those slanted mounts. You could just rotate the globe's support with the base flat on your surface.

The precession of Earth's axis also means that Polaris is not fixed as the north star. The north celestial pole cycles over those 26,000 years between pointing at Thuban in Draco, Polaris, Gamma Cephi, Vega, and some other stars.

In a similar vein, with all the stars following slightly different orbits around the center of the milky way, the night sky changes over long periods of time. Over the coming hundreds of millennia, the stars in the familiar constellations will slowly scatter. At some point, I expect we will have to come up with new constellations.
 

mjennings

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My middle school gifted program science teacher and I spent a large part of a class talking past each other about Earth's orbit because I understood that the orbit was an ellipse and that parhelion was near the northern winter solstice and aphelion near the N summer solstice, but didn't have the vocabulary to get that across.
She was a good teacher and put up with me when I put my feet up and announced I was bored in a different unit. There were only about 8 if us in the class and she and my parents had a good laugh at teacher conferences that year.
 

Funkworks

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A lot of desk globes have those slanted mounts. You could just rotate the globe's support with the base flat on your surface.
I think maybe they all have the slant, but I want one where the slant (tilt or obliquity) is variable. And maybe I could run the rotation, slant oscillation and precession (a turntable! why not!) with 3 motors and have a better model of what an oblate spheroid can do.

Fun fact:
The main differences between any two stars are their mass, age and composition, and this largely dictates their luminosity.
 
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jqavins

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-Jupiter's magnetosphere is the largest thing in the solar system. If it was visible, it would be 2-3 times the size of the sun/moon as seen from Earth.
This surprises me greatly. I should expect the sun's magnetosphere to dwarf Jupiter's, since the sun's anything generally dwarf's any other object's same thing in the solar system. But I can't find any statement of the sun's magnetosphere's size, so I must remain surprised, if skeptical.

Mercury's orbit is not only elliptical, the ellipse itself rotates around the sun (and this remained unexplained for 200 years).
Isn't that true of all the planets, and just most noticeable with Mercury?

I demonstrated that a van de graf , fed hydrogen, can make a silver coin radioactive for a bit
Oh, do tell! I guess maybe this isn't the right thread.

He was an associate of David Halliday and Robert Resnick (who'd written the book)
Halliday & Resnick is "the book" in a huge number of physics classrooms, high school senior and college freshman alike.

On the National Mall in Washington, DC, there is a 1:10,000,000,000 scale model of the solar system, from the sun to Pluto. At that scale, it is nearly 2,000 feet (a little over 1/3 of a mile or 3/5 of a kilometer) long, the sun is a smidge under 5½ inches in diameter, Earth is about 1/20 of an inch, and Pluto is about 1/100 of an inch (a quarter millimeter, smaller than most pencil dots, only about 2½ time the size of a human ovum).
 
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KilroySmith

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If the Sun were the size of a Basketball, the Earth would be half the diameter of a BB (2.2 mm), and would be 26m/86ft away (the distance from the center of one basket to the other on a Basketball court). Jupiter would be 25 mm in diameter (2/3 the size of a ping-pong ball), and would be 135m away. Pluto would be invisibly small (250 microns), and a kilometer away. The moon would be about twice the size of Pluto, and about 6.6cm away from the earth.

I was going to put together a "realistic" solar system for the kid's science classes in high school, to demonstrate that the pictures in their science book were...uhh...somewhat unrealistic. Kind of a "Everyone you know, and everywhere you've ever been, is a tiny dot on this tiny little sphere". Figured I come in with a boxful of balls of various sizes (baseballs, ping pong balls, BBs, various sizes of ball bearings, etc) and let the kids decide how big each planet was relative to the Basketball sun, then show them reality.
 

Funkworks

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Isn't that true of all the planets, and just most noticeable with Mercury?
Yes, but for other planets, it can be accounted for by their neighboring planets with Kepler and Newton's mechanics. In the case of Mercury, it cannot and you have to go through what SecondRow went through (a rabbit hole, arguably never-ending) to calculate what astronomers see:

My Relativity final exam many many years ago was to calculate the precession of Mercury. Fun with tensor math!
There's actually a movie about this! Solving this problem is the first thing that made Einstein a household name. No one bothered with General Relativity very much until it became the only way to calculate Mercury's orbit and then A.E. became Elvis (until the real Elvis came along in the 50s).

Fun fact (to keep me on track)
- Solving the 200-year old Mercury problem is what first made Albert Einstein a public figure (by Eddington who was already well-known).
 
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smstachwick

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Imagine Earth represented by a basketball, and the Moon represented by a baseball 25 ft away. That’s approximately scale.

When President Kennedy set the goal for humans to land on the moon by the end of the 1960s, all human spaceflight had taken place at an altitude represented by just a few millimeters from the basketball’s surface. People at NASA heard what he wanted them to do and thought he was nuts, and perhaps he was. But by golly, they did it, and it was more epic than anybody who wasn’t there (myself included) can truly comprehend.

I’d love to see a crewed Moon landing in my lifetime. I’d skip work and pull an all-nighter to see it.
 

SecondRow

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I hope you nailed it. Isn't it weird that tensor calculus is useful for AI machine learning and for astrophysics?
I smoked that class. 👍 Relativity and QM were my favorite classes as a physics major. The math just came easy to me, even if the actual phenomena were difficult to comprehend. Unfortunately, I did not enter the field, and it was 20+ years ago, so I‘m pretty sure I’d fail that final today. 😂
 

Blast it Tom!

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Imagine Earth represented by a basketball, and the Moon represented by a baseball 25 ft away. That’s approximately scale.

When President Kennedy set the goal for humans to land on the moon by the end of the 1960s, all human spaceflight had taken place at an altitude represented by just a few millimeters from the basketball’s surface. People at NASA heard what he wanted them to do and thought he was nuts, and perhaps he was. But by golly, they did it, and it was more epic than anybody who wasn’t there (myself included) can truly comprehend.

I’d love to see a crewed Moon landing in my lifetime. I’d skip work and pull an all-nighter to see it.
I saw the first one!

But yeah, let's get going again. Seriously. In that vein,

"Fun" space fact:
If the Earth were a basketball, since the end of Apollo, no human has been more than 5/32" (4 mm) from the earth's surface.

You guys amaze me with your knowledge.
 

teepot

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I saw all of the launches from Mercury to Apollo. When 2001 came out I looked at it as a prediction of the future. As we got closer in time to the real 2001 I became more and more sure it wouldn't happen in my lifetime. I am bummed. The only hope I have left is that ET comes for a visit in my lifetime. I'm 65.
 

smstachwick

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I saw all of the launches from Mercury to Apollo. When 2001 came out I looked at it as a prediction of the future. As we got closer in time to the real 2001 I became more and more sure it wouldn't happen in my lifetime. I am bummed. The only hope I have left is that ET comes for a visit in my lifetime. I'm 65.
Keep a thing of Reese’s Pieces at the ready.
 

Funkworks

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This surprises me greatly. I should expect the sun's magnetosphere to dwarf Jupiter's, since the sun's anything generally dwarf's any other object's same thing in the solar system. But I can't find any statement of the sun's magnetosphere's size, so I must remain surprised, if skeptical.
I think you're right about the Sun's, but they call that one the "heliosphere" instead :rolleyes:.
https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter
"...after the heliosphere"

My turn:

"Jupiter has 53 named moons and another 26 awaiting official names. Combined, scientists now think Jupiter has 79 moons." 🌕
 
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Antares JS

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-Venus rotates in retrograde, very slowly. Its sidereal rotation period is longer than its year at 243 and 225 earth days, respectively. The solar day as viewed from the surface is 117 earth days and the sun would rise in the west and set in the east if it was visible from the surface.

-Jupiter and Saturn have rotation periods of only about 10 hours. All that mass rotating so rapidly makes them noticably ovoid, squashed at the poles and bulging at the equator.

-Uranus was discovered entirely by accident by English astronomer William Herschel in 1781, and after realizing he had discovered a new planet, wanted to name it George's Star after George III, King of England and his patron. This didn't sit well with the international astronomical community and the planet was officially named Uranus, since he was the father of Saturn, who was the father of Jupiter. Some English organizations kept calling it George's Star until 1850.

-Astronomers pronounce Uranus "YER-ah-nus," with the stress on the first syllable and short a sound in the second syllable. I have habitually used this pronunciation after months working at Space Camp teaching kids about the solar system.

-Neptune was actually first spotted by Galileo as it moved near Jupiter relative to Earth. He was observing the moons of Jupiter and noted a faint star behind Jupiter. Whether Galileo thought it was just a star or recognized it as a planet is not known for sure, but reading his notes reveals that Galileo did notice that Neptune moved relative to the background stars.
 
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jqavins

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I saw all of the launches from Mercury to Apollo. When 2001 came out I looked at it as a prediction of the future. As we got closer in time to the real 2001 I became more and more sure it wouldn't happen in my lifetime. I am bummed. The only hope I have left is that ET comes for a visit in my lifetime. I'm 65.
I should have been paying closer attention to the Apollo landings. I was only five for the first one, so it's understandable that I wasn't, but I turned nine while the last was on the surface, and I kick myself for not being more aware at the time. I expect to be around for the next one, as it's most likely coming within five years. I don't expect crewed missions to Jupiter or beyond in my grandchildren's lifetime, let alone mine. And I have little to no hope that FTL travel is fundamentally possible, so ET is simply not coming.

Astronomers pronounce Uranus "YER-ah-nus," with the stress on the first syllable. I have habitually used this pronunciation after months working at Space Camp teaching kids about the solar system.
Isn't it more "YER-ə-nəs"?
 
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jqavins

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Ə ə are called "schwa", and are pronounced like a soft grunt. Like the double 'o' in "good".
 

Funkworks

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The rotational axes of Uranus and Pluto are very tilted:
main-qimg-66a2ec05ec63b7375627853c3ea93a94.jpeg
 
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