[HN Gopher] Proof That the Earth Spins
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Proof That the Earth Spins
Author : nyc111
Score : 43 points
Date : 2022-02-07 18:11 UTC (4 hours ago)
(HTM) web link (profmattstrassler.com)
(TXT) w3m dump (profmattstrassler.com)
| jpatte wrote:
| High precision gyroscopes showing a 15 degrees per hour drift?
|
| Thanks Bob! :-)
| mac-chaffee wrote:
| Why the need for a perfect gyroscope that can spin for 24 hours?
| Why not use a motor to counteract the slow-down without affecting
| the rotation? Science museums sometimes do this to their Foucault
| Pendulums so they don't need to keep re-swinging them:
| https://www.pugetsound.edu/about-puget-sound-0/leadership/20...
| geuis wrote:
| > if you watch carefully, you'll see none of them are heading
| west.
|
| I've seen this posted twice in different places by different
| people this week. It's not true.
|
| While _most_ satellites are west to east (or in polar orbits),
| most Israeli sats orbit east to west. This is because their
| launch center is on the west coast of their country and it 's not
| good for them to be launching rockets over their neighbors.
| breck wrote:
| I'm not an expert but looks like you're right.
|
| > Shavit rockets are launched from Palmachim Airbase by the
| Israel Space Agency into highly retrograde orbits over the
| Mediterranean Sea to prevent debris coming down in populated
| areas and also to avoid flying over nations hostile to Israel
| to the east; this results in a lower payload-to-orbit than
| east-directed launches would allow
|
| https://en.wikipedia.org/wiki/Shavit_2
| koheripbal wrote:
| One of many hidden costs of conflict in the middle east.
| nyc111 wrote:
| I wonder why Prof. Strassler does not consider star trails, like
| here, https://en.wikipedia.org/wiki/Star_trail definitive proof
| of Earth's rotation. In historic times astronomers invented
| crystalline spheres [1] that carried stars to save the stationary
| earth doctrine. But now we know that crystalline spheres do not
| exist (stars have their own proper motions) so since stars do not
| rotate, the earth must rotate. What's wrong with this argument?
|
| [1] https://en.wikipedia.org/wiki/Celestial_spheres
| allturtles wrote:
| In this post and your subsequent replies you rely on the
| existing astronomical body of knowledge to show that the Earth
| spins.
|
| This misses the point of the OP, which is to try to provide a
| simple physical demonstration that anyone could perform or
| witness which shows that the Earth spins, in particular one
| that's more intuitive than Foucault's pendulum.
| cuteboy19 wrote:
| Newtonian mechanics does not have absolute speed. We can only
| say A is moving at 5m/s relative to B.
|
| But Newton does have absolute acceleration. So we can say A is
| accelerating at 5m/s2 without even thinking of B.
|
| Since a rotating body accelerates, we should be able to say
| that the earth rotates without even thinking of the sky.
|
| The proof does exactly this. Looking at a gyroscope is
| sufficient to prove that the earth rotates. No need to look at
| the sky
| nyc111 wrote:
| But the gyroscope looks at the sky, it points at the same
| star, right? This is how the proof works.
| cuteboy19 wrote:
| Imagine that you live in a starless void. Could you still
| prove that the earth spins?
|
| Yes, simply point the gyroscope towards an arbitrary
| direction and repeat the same process as in the proof.
|
| If the earth doesn't spin, then the gyroscope would point
| at the same direction always. But if it does spin then it
| would show those circles.
| marcosdumay wrote:
| The author also seems think Foucault pendulums aren't
| conclusive. That one is much harder to argue against than star
| trails (there's no need to prove the absence of celestial
| spheres or other kinds of star movement).
|
| Honestly, I don't see much difference between a gyroscope
| experiment and the Foucault pendulum. Except that the later is
| much easier to do.
| dwohnitmok wrote:
| As the article notes, the Foucault pendulum is slightly more
| work to prove. Nothing beyond high school math, but it's less
| obvious than "once you point this gyroscope at any star, it
| keeps pointing at that star no matter how that star moves,
| how could that be if the stars are moving but not the earth?"
| sandworm101 wrote:
| >> how could that be if the stars are moving but not the
| earth?
|
| Because maybe the earth is fixed, the heavens all move, and
| the pendulum is reacting to the heavens. Maybe a tidal
| force from the stellar spheres is imparting a slight motion
| on the pendulum. Maybe only objects like gyroscopes are
| sensitive enough to feel this force.
| dwohnitmok wrote:
| Oh it's definitely possible to have alternative theories
| but they get increasingly outlandish as you make small
| modifications. E.g. "how does a gyroscope know which star
| to point at? What happens if the gyroscope points at the
| middle between two stars? What happens if you point it at
| a star that has not yet been discovered (e.g. more
| powerful telescopes reveal it in the future)? Do
| different stars have different effects?"
|
| Trying to answer these questions makes the stellar
| spheres theory require more and more ad-hoc additions to
| support.
| NineStarPoint wrote:
| What's wrong with your argument is it assumes facts that
| themselves need to be proven. "Stars have their own proper
| motions" is not an easy fact to prove, and it took a very long
| time for people to prove that "stars do not rotate" (I presume
| you mean around the earth). The sort of thing being discussed
| here is the sort of thing you need to do to prove that
| crystalline spheres do not exist. There are of course other
| ways to prove that crystalline spheres do not exist, but they
| are things like the existence of black holes or the speed of
| light. And in general, all these sorts of things require a much
| broader knowledge base/trust in our current understanding to
| prove the idea that the earth rotates.
|
| This article is saying that if you can prove how a gyroscope
| works (itself requiring proof of the Conservation of Angular
| Momentum), you can show that the earth rotates. Which is
| ultimately a much simpler thing to prove than things about the
| nature of the stars themselves.
| [deleted]
| nyc111 wrote:
| We know stars are distributed in various distances, this we
| know by observation. If not the earth but the stars rotate we
| must assume that billions of crystal spheres at different
| distances somehow rotate in exact coordination to trace the
| star trails that we observe. I don't think there is such a
| huge "conspiracy" of crystal spheres to fool us.
| codethief wrote:
| > We know stars are distributed in various distances, this
| we know by observation.
|
| How do we know? Establishing the cosmic distance ladder
| requires far more elaborate tools than the ones discussed
| here (Special and General Relativity, for instance) and the
| necessary measurements and observations also presume in one
| way or another that Earth is rotating. Even if you're only
| talking about stars in our immediate neighborhood for which
| a distance measurement merely needs the parallax effect
| (instead of SR or GR): In this case the parallax effects
| _literally_ rests on the rotation of Earth and its orbit
| around the sun.
| nyc111 wrote:
| > the necessary measurements and observations also
| presume in one way or another that Earth is rotating.
|
| Yes, the lack of star parallaxes were the main argument
| offered by Tycho Brahe against a moving earth theory.
| When star parallaxes were observed the motion of earth
| was accepted. The way I understand it, to measure star
| parallaxes the earth must move. This is not an
| assumption, there is no circular reasoning. And we
| observe different parallaxes for different stars, meaning
| that stars are not all on the same distance from earth. I
| don't know if this is a trend like flat earthers to say
| that all stars are the same distance from the center of
| the universe?
|
| > In this case the parallax effects literally rests on
| the rotation of Earth and its orbit around the sun.
|
| So, this way you prove that the earth moves and stars
| have different parallaxes and are not all attached to a
| crystal sphere. I don't see a problem here.
| throw0101a wrote:
| > _Yes, the lack of star parallaxes were the main
| argument offered by Tycho Brahe against a moving earth
| theory._
|
| Much earlier than Brahe. Aristotle in _De Caelo_ (Book
| II, part 14):
|
| > _The earth, then, also, whether it move about the
| centre or as stationary at it, must necessarily move with
| two motions. But if this were so, there would have to be
| passings and turnings of the fixed stars. Yet no such
| thing is observed. The same stars always rise and set in
| the same parts of the earth._
|
| * http://classics.mit.edu/Aristotle/heavens.2.ii.html
|
| * https://en.wikipedia.org/wiki/On_the_Heavens
| sandworm101 wrote:
| Stars can still have parallaxes while bolted to the
| spheres. Maybe the spheres themselves wobble a little.
| Maybe the motion of the sun around the earth imparts a
| slight motion to closer spheres. The fixed stars are
| obviously on spheres far enough away that the sun doesn't
| shake them.
| nyc111 wrote:
| "Stars have their own proper motions" is not an easy fact to
| prove. . ."
|
| No, proper motions are well known,
| https://www.britannica.com/science/proper-
| motion#:~:text=pro....
|
| So we must further assume that a star attached to a crystal
| sphere will have a separate motion which also need to be
| explained.
| IanCal wrote:
| It's well known that the earth rotates too though.
| sandworm101 wrote:
| >> a star attached to a crystal sphere will have a separate
| motion
|
| Two spheres. Proper motion can be explained completely if
| we allow each star to exist on its own crystal sphere.
| Layers of spheres could also extend great distances. Maybe
| the universe is vast, but it is all spheres. What does
| disprove spheres are collisions of objects having different
| proper motions.
| nyc111 wrote:
| > Two spheres. Proper motion can be explained completely
| if we allow each star to exist on its own crystal sphere.
|
| Wow! I can believe we are discussing in the age of Hubble
| space telecope and Webb etc. the existence of crystal
| spheres and how they can explain motions of stars. I
| don't believe crystal spheres exist but I respect your
| belief in them. To me they are an unnecessary and
| cumbursome explanation.
| sandworm101 wrote:
| As cumbersome as unobserved massive particles
| representing the majority of matter in the universe?
| littlestymaar wrote:
| > This article is saying that if you can prove how a
| gyroscope works (itself requiring proof of the Conservation
| of Angular Momentum)
|
| Which means we're already in the domain of Newtonian
| mechanics, which came almost 80 years after Kepler's _laws of
| planetary motion_ which gave us a clear understanding of the
| motion of a bunch of "stars" (yes, planets are not stars but
| they have the same kind of "star trails").
|
| The really cool thing about star trails is that it's
| something really intuitive and easy to observe, and as such
| it makes a pretty convincing "proof" of earth rotation.
| Unlike the "proof" in this article, which will leave most
| people unimpressed (and which as I said earlier, uses a much
| more advanced physics theory than what's needed if you really
| want to prove earth rotation with star trails).
| moffkalast wrote:
| It doesn't account for the option that the Earth is stationary
| and the sky is spinning, much it like it would be implemented
| in a game or CGI scenes for example.
|
| Gyroscopes can rule this out as well since they're showing
| rotational change directly.
| KineticLensman wrote:
| > In historic times astronomers invented crystalline spheres
| [1] that carried stars to save the stationary earth doctrine.
|
| My understanding is that the ancients used the celestial
| spheres to explain the movements of the planets around the
| Earth - the spheres themselves moved relative to each other
| hence the different speeds and courses of the planets.
|
| The spheres could be made to work regardless of whether the
| Earth spins or not. If the Earth is static, then the spheres
| can still use their relative motions to explain the motion of
| the planets. In contrast, if the Earth is spinning, you add its
| spin to that of the spheres and an observer on Earth couldn't
| tell the difference.
| danschumann wrote:
| Coriolis will actually effect a long range projectile, but not by
| much.. (basically the earth spinning under a bullet with a
| sufficiently high arc).
| MengerSponge wrote:
| Yes! While it's technically true, this has evolved into an
| urban legend about southern hemisphere naval battles during
| WWI.
|
| https://skeptics.stackexchange.com/a/44760
| pdonis wrote:
| The gyroscopes described in the article actually, if we measure
| with sufficient precision, will _not_ keep pointing in exactly
| the same direction as determined by distant objects. They will
| precess. Heuristically, the precession has three components:
|
| (1) Thomas precession;
|
| (2) De Sitter or geodetic precession;
|
| (3) Lense-Thirring precession.
|
| The first two are due to the rotation of whatever platform the
| gyroscope is riding on, in this case the Earth, so they are also
| evidence for the Earth's rotation. The second is due to the
| spacetime curvature produced by the Earth. (The third also
| involves spacetime curvature, through effects on it due to the
| Earth's rotation.)
|
| (Note that these effects are separate from the effects of
| imperfect isolation of the gyroscope, which the article
| discusses.)
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