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Cosmology, Peanut Gallery

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Peanut shells, mankee feces, used polar bear condoms go here.

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PLEASE EXCUSE THE ANNOYING COMMERCIAL BREAKS IN THE CONVERSATION:

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And now, back to the regularly scheduled conversation...



This is likely a peanut gallery item for BAA's first post on the Copernican Principle.

 

How long did it take human civilization to accept the Heliocentric Model?

 

Which centers of authority (e.g., European kingdoms, religious institutions, minor fiefdoms) embraced the new science?

 

Which attempted to subdue/eliminate it?

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Peanut Gallery is for those who are Not in the Discussion so monitored.

 

Please allow Fwee to get things going prior to commenting.

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Given that BAA has moved his initial post over to the other thread, I'm assuming the peanut gallery is now open?

 

I think the first post was great. There are just a couple points I would like to raise. This is more of a general commentary than a question, so it probably belongs here. BAA, feel free to respond, but please don't feel obligated to.

 

First, I'd like to point out that heliocentrism was actually proposed by the ancient Greeks (Aristarchus of Samos). Unfortunately, the records are lost, and the theory never gained much traction. The result was that it was all but forgotten during the time that BAA is discussing.

 

I think it also bears noting that religion was not the only reason that heliocentrism (as proposed by Copernicus) was initially rejected by many. To us this rejection seems absurd, but we are looking back at this theory through the lens of our modern understanding of physics. At the time, Aristotelian physics was the only physics they had (this was over 100 years before Newton). The heliocentric model proposed by Copernicus was not without its problems. It did not propose a mechanism by which the planets remained in orbit around the Sun (ie, universal gravitation). It did not provide an explanation for how such a massive object as the Earth could be moved. On Aristotelian physics, the assumption that an object as massive as the Earth should be stationary is entirely reasonable. Celestial objects (stars, planets, etc) were hypothesized to consist of an entirely different substance (aether) which could allow their motion to be much more easily accounted for. Thus there were initially good scientific reasons for being critical of the Copernican view (of course, there were also the religious reasons, which certainly played a role).

 

The transition from a geocentric to a heliocentric view of the solar system did not happen all at once. Shortly after Copernicus' theory was put forth, there was another model which was proposed by Tycho Brahe. This was a sort of hybrid model, which held that some of the planets orbited the Sun, but that the Sun orbited the Earth. This model also worked quite well mathematically. This is important to note because both Copernicus’ theory and Tycho’s theory were entirely geometric. Both were imperfect, and neither could explain why anything orbited anything. It took a very long time for Tycho’s theory to die out and the Copernican model--with revisions by Kepler, who, incidentally, was a former assistant of Tycho Brahe--to become accepted by virtually everyone. And this is how it should have been. Novel scientific theories should not be accepted immediately, even if they seem to work. Both the Tychonic and the Copernican view worked. Neither was complete. The Tychonic system did not die out completely until the early 1700s.

 

edit: spelling

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All good points, D.

 

Not overlooked nor disregarded, I can assure you.

It's just that to keep the tutorial thread streamlined and on-track it's necessary to sacrifice certain fine detail to get the salient points of the message across.  I'm sure you understand.

 

Thanks,

 

BAA. 

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All good points, D.

 

Not overlooked nor disregarded, I can assure you.

It's just that to keep the tutorial thread streamlined and on-track it's necessary to sacrifice certain fine detail to get the salient points of the message across.  I'm sure you understand.

 

Thanks,

 

BAA. 

 

Of course I understand. The above was not intended as criticism. I enjoyed your post quite a bit. I particularly liked the illustrations of epicycles. Very helpful when trying to visualize retrograde motion. Keep it up!

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Graciously offered and gratefully received, D.  smile.png

 

What else is a peanut gallery for but points arising from another thread?

 

Thanks,

 

BAA. 

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Rule, one of very few.

 

PARTICIPANTS in locked discussion this thread are disallowed use of Peanut Gallery.

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Rule, one of very few.

 

PARTICIPANTS in locked discussion this thread are disallowed use of Peanut Gallery.

Sorry, I don't understand this rule, can you please explain? thanks.

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Rule, one of very few.

 

PARTICIPANTS in locked discussion this thread are disallowed use of Peanut Gallery.

Sorry, I don't understand this rule, can you please explain? thanks.

 

 

Seconded.

 

A clarification would be appreciated.

 

Thank you.

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The transition from a geocentric to a heliocentric view of the solar system did not happen all at once. Shortly after Copernicus' theory was put forth, there was another model which was proposed by Tycho Brahe. This was a sort of hybrid model, which held that some of the planets orbited the Sun, but that the Sun orbited the Earth. This model also worked quite well mathematically. This is important to note because both Copernicus’ theory and Tycho’s theory were entirely geometric. Both were imperfect, and neither could explain why anything orbited anything. It took a very long time for Tycho’s theory to die out and the Copernican model--with revisions by Kepler, who, incidentally, was a former assistant of Tycho Brahe--to become accepted by virtually everyone. And this is how it should have been. Novel scientific theories should not be accepted immediately, even if they seem to work. Both the Tychonic and the Copernican view worked. Neither was complete. The Tychonic system did not die out completely until the early 1700s.

 

edit: spelling

 

This is true, and indeed the hallmark of Newton's theory of gravity (which most college physics students are familiar with) is that it provides a predictive model which allows the orbits of hypothetical planetary systems to be predicted.  Newtonian gravity also provides an explanation, albeit a contrived one in which the principle of action at a distance must be invoked.  I'm currently preparing an installment on the general theory of relativity in which I'll touch on this briefly.

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Rule, one of very few.

PARTICIPANTS in locked discussion this thread are disallowed use of Peanut Gallery.

Sorry, I don't understand this rule, can you please explain? thanks.
 Seconded.

 

A clarification would be appreciated.

 

Thank you.

Will get back to you (FTNZ & BAA) on this.

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If you are one of the Participants in protected thread you are disallowed use of PG.

 

PG simply is here for outsiders to make their own commentaries and opinions.

 

IF those in discussion permitted to answer outside, information/discussion becomes less centered and more like a typical manner feces tossing.

 

k

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OK, so one is either able to post in this thread or the other, but not both?  Or is it only strictly non-relevant questions go here in the PG? I still don't get it completely. I guess I'll wait and see.

 

Either way, I understand the need to keep the main cosmology thread clean and I'm all for that.   I've been looking forward to it like crazy and I don't want to see it turn into a debate or discussion of conflicting ideas either...I just want to learn, and I'm all for whatever will keep this new little classroom from getting mucked up.

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Only BAA, Bhim and Roguescholar are to post in the main Cosmology thread. Think of that thread as being for the teachers only.

 

Anyone with serious inquiries only (about the material from the main thread), can post them here in the peanut gallery.

 

That's ANYONE -- hopefully some Christians, too. Again though, this is only for SERIOUS inquiries. If a christian steps in and tries challenging the main thread by attempting their square-peg-in-round-hole routine (meshing theology with cosmology), those posts will get snuffed.

 

This is strictly for educational purposes only. Not debate.

 

Easy enough?

 

And of course, BAA, Bhim and Roguescholar are certainly free to answer posts within this thread.

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Thanks for the clarification Fweethawt.

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And of course, BAA, Bhim and Roguescholar are certainly free to answer posts within this thread.

??? This seems to contradict what Kevin said.

 

Confused.

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And of course, BAA, Bhim and Roguescholar are certainly free to answer posts within this thread.

??? This seems to contradict what Kevin said.

 

Confused.

You are correct. It does.

 

And that is because Kevin was confused on the reasons for the two threads. We ironed things out an are on the same page now.

 

Main thread = teachers ONLY

Peanut Gallery = teachers AND students but no bullshitters.

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Nice second post BAA.

 

I would like a bit more information about how the distances in space are measured. The whole process has never really been clear to me. I understand that parallax plays a role, as does relative brightness, but I'd like a bit more detail about what precisely is measured (and how), and how the ensuing calculations are actually done.

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That is a tall order and unfortunately, time is very limited for me right now, but I'll give it a go. How are you on your trigonometry? I will explain how we can use parallax to determine distances to nearby objects and you need a basic understanding of trig and the fundamental trig functions in reference to a right triangle.

 

Edit: Irrelevant info deleted.

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So, let us use trig and parallax to identify the distance to a hypothetical object that is nearby. This fails when objects are very far apart however and we need to use standard candals for those distances, but let me discuss a little trig. Please note the picture that I drew below. This is a right triangle.  The right angle is at 90 degrees and let us choose the another angle up at the top left of the picture.  We will call this angle Theta (circle thing with a line through it). To find this angle, we need to know how long the sides of the triange are. Likewise, if we knew the angle, we would know something about how long the sides are. We can find this out by using the concept of SOH-CAH-TAO:

 

Sine (Theta) = opposite/hypotenuse

Cosine (Theta) = adjacent/hypotenuse

Tangent (Theta) = opposite/adjacent

 

The shorter side that makes up part of Theta is called the adjacent side, the longer side that makes up the other part of Theta is known as the hypotenuse and the side away from the angle is known as the opposite side.

 

Trig

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Now, appreciate the picture below:

 

Look at 1; this is the earth at a certain point (left lower part of the picture). The sun is red, larger and above the Earth at position 1. At position 1, imagine looking straight up in the night ske.  That is the black line on the bottom, going away from the earth.  Notice there is a star in the sky and the star will be at some angle from "stright up."  Now, look at the Earth at position 2 (top left of the figure). Again, you can see the black line as loking "striaght up" and the star that we are looking at.

 

So, let's say we know where the sun is and the distance to the sun. (93,000,000 million miles or so). The star is at some angle Theta prime (') from "straight up." The distance to the sun is line A. You see, we can draw a line from the sun to the distant object and a line from the earth to the sun.  These lines will make a 90 degree right angle.  Next, let us assume the angle Theta' is 10 degrees.  That would mean that the angle That would simply be 90 degrees - 10 degrees (80 degrees). So, now we know how long the adjacent line is (93,000,000 miles) and we know the angle Theta is 80 degrees. If we knew how long the opposite line was (X on the picture), we would know the distance from the sun to the star.

 

This is where the trig comes into play. If we select the tan = opp/adj function, we will have our answer:

 

So, Tan Theta (80degrees) = opp/adj

 

Take Tan of 80 degrees and get 5.67

 

Rewrite the equation as: 5.67 = opp/adj

 

Put in the known distance of the adjacent (93,000,000 miles)

 

Rewrite the equation as: 5.67 = opp (x)/93,000,000

 

Multiply both sides by 93,000,000 miles

 

X = 527,000,000 miles or 5.27 *10(8) miles

 

Double check my math but for an ad hoc, table top exercise that should do for a basic introduction...

 

Star Distance

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Thanks RS, that's a nice explanation of the trigonometry involved. I appreciate you taking the time to write it up. Unfortunately for me, this is the part that I already understood. I should have made my question more clear.

 

Calculations such as the one you showed involve at least one measured distance. It doesn't suffice to only measure angles. In the example you gave, the distance you used was the distance from the Earth to the Sun. How is this measured?

 

Also, as you point out, this only works for stars which are nearby. You mention the use of "standard candles" to compute the distance to much more distance stars and galaxies. I understand in principle that this can be done, but I'm not very clear about how the absolute magnitude of a particular star is determined. I have no issue with the idea of absolute vs apparent magnitude, I'm just not very clear on how we find an absolute magnitude and then use it to determine distances.

 

My knowledge of math is fairly strong, as is my general understanding of physics. These should not be barriers to your explanation. I'm also not in any sort of hurry. I appreciate you taking the time to explain this to me at all. Please respond as your schedule allows.

 

Thanks again.

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Nice second post BAA.

 

I would like a bit more information about how the distances in space are measured. The whole process has never really been clear to me. I understand that parallax plays a role, as does relative brightness, but I'd like a bit more detail about what precisely is measured (and how), and how the ensuing calculations are actually done.

 

Thanks, D.

 

As RS says, this is a tall order.

 

To give you an idea of the complexity involved, please look at this Wiki page.  http://en.wikipedia.org/wiki/Cosmic_distance_ladder

 

The RogueScholar's dealing with parallax, so it only remains for me to comment that parallax is good out to a certain distance and then other distance-measuring techniques take over.  Edwin Hubble used the Cepheid Variable technique, which in a very small nutshell, works like a standard candle because there's a proportional relationship between the brightness of these stars and the duration of their variability.  

 

A Cepheid pulsates, changing brightness over a (more or less) fixed cycle.

The longer the period of their pulsation the brighter their absolute magnitude (brightness).  Therefore, if you see a very long period Cepheid that's also extremely faint, you know that this faintness cannot be due to the star being small and dim.  This (very briefly) was the method Hubble used to discover that the Andromeda Nebula (thought be to small and inside the Milky Way) was actually the Andromeda Galaxy and was million of light years distant.

 

Certain types of supernovae are also considered to be standard candles because the curve of their light output decays in a (more or less) fixed way.  Because these explosions are so powerful, they can seen clear across billions of light years of inter-galactic space.  They are therefore a major part of the distance ladder.

 

Any and all improvements to any part of the ladder will improve the whole system.

This is why the final results from the Gaia mission... http://sci.esa.int/gaia/ ...are so keenly anticipated.  They will give us an excellent measure of distances and positions of a billion stars within the Milky Way.

 

Thanks,

 

BAA.

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The earth to sun distance can be calculated in several ways, but the parallax method as I described above can be slightly modified to incorporate observers in different places on earth. This has also been done using the moon and transits of other planets. Either way, you make a triangle and crunch the numbers.

 

Knowing the mass of the sun can allow us to use basic Newtonian equations that make use of centrifugal and gravitational force calculations and solutions. Unfortunately, I am on my phone right now and cannot properly draw and "derive" all of this for you. However, I hopefully have armed you with enough knowledge to easily find exact answers.

 

If you allow me some time, I will try to get additional diagrammes and math until for you that explains how standard candles can be used. It's a fascinating story and it illustrates the critical role women played in this story; particularly during a time when women were quite oppressed. It's quite remarkable.

 

If somebody beats me to the punch, all the better. However, I plan to have something up this afternoon when I get back to my office. Unfortunately, after this weekend I may be generally unavailable for several days, so I may not be able to elaborate if additional questions come up.

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