The Oort Cloud Explained

[dcarrera]

Why grasp at straws to explain comets?

Why is it grasping at straws? We actually see long-period comets, and they actually do have very large semi-major axes. Every single long-period comet is an actual example of an object that spends most of its time much farther from the Sun than the Kuiper belt.

 

[dcarrera]

Unless you can prove that distance your radius is worthless. You can't.

For a star only 40pc away we can easily measure its parallax, which gives its distance.

 

[dcarrera]

There is a background glow in the observable universe. That glow is observed on and near earth. In no way does that mean a big bang. It also fits a creation model.

Really? Can you use the creation model to predict the anisotropy distribution of the CMB and show that it fits the data of the Planck satellite at least as well as the LCDM model?

 

[dad]

I have already explained that it is extrapolating into the future what has been observed in the past. The prediction of future light maxima or minima is based on the period obtained from past maxima and minima.

Unrelated to science then, except they sit and watch something happen.

No, I am not kidding. The behaviour of variable stars tells astronomers a lot about stellar structure and the physics of pulsation, and about mass transfer between binary stars.

In other words you try to squeeze in your earth nature law explanations for what we see far away..after the fact!!!!

I am not sure what this means. Perhaps you mean that making a prediction requires analysis of observations or having an understanding of the physics governing the observed phenomenon, or both. If so, I agree with you.

Take a person who predicts weather. If all they did was sit there and tell you what they saw yesterday, most of us would not consider that a prediction of things to come. If a psychic predicts that JFK got assassinated back in 1963, that is not much of a prediction. If I see a light go on in a room set to a timer every night at 8pm and predict it will go on all week, that is a mickey mouse prediction.

 

[dcarrera]

The name 'Oort Cloud' makes me think of old school Power Rangers or Star Trek

Also, I don't understand why something like that can't be seen. We can find Pluto but not this gigantic tirade of junk.

Pluto is bigger and closer, and that makes it much easier to see. The brightness of a distant object that is illuminated by the Sun is proportional to the object's surface area divided by the fourth power of the distance to the Sun.

Luminosity of Pluto ~ (radius of Pluto)^2 / (Sun-Pluto dist2ance)^4

So we can compare Pluto and a 1km Oort cloud object at (for example) 1000 AU:

(r_pluto^2/a_pluto^4) / ( (1km)^2 / (1000au)^4 ) = 5.9e11

So, Pluto would be about a trillion times brighter than our sample Oort cloud object. If there are a trillion such objects, and for simplicity we put them all at 1000 AU, their total brightness might be comparable to Pluto, but it would be spread out the entire sky.

I will add a reminder that we really do see long-period comets, and those comets do have orbits that would put them very far from the Sun most of the time. Every single long-period comet is a real world example of an observed Oort cloud object.

 

[dcarrera]

Trillions upon trillions of small chunks vs one Pluto, and Pluto goes right up in the Kuiper Belt.

It is not one Pluto, it is an entire Kuiper belt. But no matter. Why does it matter if there are trillions of them? We are still talking about being able to observe one of them. If you put a Pluto-clone at 400 AU (best case scenario), it will be about 10,000 times dimmer than Pluto because the brightness of a distant object that is illuminated by the Sun goes down with the fourth power of the distance. If you put the Pluto-clone at 4,000 AU, or 40,000 AU, it would be 100 million or 1 trillion times dimmer than Pluto.

 

[dad]

Astronomers observe the movements of a comet against the frame of reference formed by the background of the 'fixed stars'. These cometary movements are used to calculate the comet's orbital elements, according to Newton's and Kepler's laws.

Right I think we get that we calculate the projected orbits.

The calculated orbital elements are used to predict the motion of the comet while it is still visible. The agreement of the observed motion with this predicted motion confirms the accuracy of the orbital elements. Do you understand so far?

A comet that has a trajectory that is short term can be treated that way. Do you comprehend that?

Now if we only ever see a comet once and the trajectory suggests it won't be seen for a million years forget about it! There are untold oodles of things that could have affected an orbit since creation! You look at just 'the present orbit'! You then assume it always was like that and will be another million years! Hilarious.

Now to come to the important point. The orbital elements of many comets, calculated, as I say, from their orbital motion, show that they have semi-major axes (a) of thousands of Astronomical Units, or even up to 20,000 AU. These comets must have orbital eccentricities (e) up to around 0.9995 in order for them to come within the Earth's orbit at perihelion. By Kepler's third law, they must have orbital periods (P) of tens of thousands or even millions of years.

Nope! Therein lies your grave mistake! Forget Keppler's law! That is short sighted if one thinks it applies to all time and space.

If comets have P ~ 10,000 to >1,000,000 years and such comets appear frequently,

How, praytell, if a comet had an orbit of a million years would it appear frequently!?

there must be a sort of 'conveyor belt' containing millions of comets that are approaching the Sun but still too far away to be visible.

Not in any way.

If these comets are distributed evenly around their orbits, most of them must be near to aphelion, at distances up to about 40,000 AU. These comets form the Oort cloud

No, they are not distributed evenly. Something likely affected the orbits, since we know the time of creation! Science doesn't know so they invented the Oort fantasy.
.

Moreover, if the distribution of the orbital eccentricities of comets is uniform, there must be 20,000 comets with e < 0.9995 for every one with e > 0.9995. Given a population of millions of high-eccentricity comets on the 'conveyor belt' bringing them towards the Sun, we now have billions of comets with e < 0.9995 that never come near the Sun and that therefore remain invisible.

Whoah! Calm down. How many comets have we seen?? Quit inventing this billions thing.

This stuff is so easy, not sure why people struggle with it

 

[dcarrera]

If you don't have a PhD, you are a layperson in my book.

I will get my PhD in astrophysics in less than a year, and I have published research. Perhaps you can count me as "not a layperson" already.

 

[dad]

Really? Can you use the creation model to predict the anisotropy distribution of the CMB and show that it fits the data of the Planck satellite at least as well as the LCDM model?

Show us the prediction for the CMB.

 

[dad]

For a star only 40pc away we can easily measure its parallax, which gives its distance.

False! You take time...time exists here on and near earth you know..and space here...that is the base line for the triangulation. We know time exists here...not at the star though. You cannot extend a time and space line to the star!

 

[dcarrera]

It only counts if they all care so much to scrutinize it. The 'overwhelming majority' also hold to dark matter & energy even though the jury is still out on that one altogether.

The jury is not "still out" on dark matter and dark energy. The evidence that they exist is extremely overwhelming. Their nature is not known, but their reality is pretty much certain.

I bet Einstein's theory would have just lit right up in his mind if he followed you all's sheep mentality with science and philosophy.

Einstein had a physics degree from one of the best universities in the world.

 

[dcarrera]

Show us the prediction for the CMB.

Sure. Here is the paper with the Planck results.

http://arxiv.org/pdf/1303.5062v1.pdf

My favorite figure is figure 19 on page 27, which I include here:

The vertical axis is the power spectrum and the horizontal axis is the angular scale. For example, you can see that most features on the CMB are around 1 degree in size. In this figure, the green curve is the prediction of the LCDM model and the red points are the data from the Planck satellite including their 1-sigma error bars. I think that the fit is impressive, but I would be interested to see the same plot using the creationist model.

 

[dcarrera]

So..blind faith in man.. not much of a defense.

Do you normally not trust experts? If your doctor tells you that you are sick and need medicine, do you consider that "blind faith in man"?

 

[dad]

Well, they must come from somewhere, and they must be going somewhere, what with Newtonian laws of motion and all

They could merely be adapting to our space and time once they get in here for all we know. Or..they could have been affected by the state change long ago...or...who knows?! We can't lock in your belief based preferences.

No, you believe that the world around you has the same limits it does everywhere else.

No. heaven operates differently. The spiritual realm operates differently...etc.

See, once you throw out the baby with the bathwater by rejecting Uniformitarianism, you must be ready to welcome in a whole slew of absurdities.

No, we then dispose of all the absurdities your belief system gave us, like the universe coming from a speck o soup, etc.

 

[The Barbarian]

DAD writes:

You think the orbital path "implies" something. That is your mistake.

It tells us, for example, whether the object has enough energy to escape the solar system, or will return. If the latter, it also tells us how far out it will go before returning, and how long that will take.

That was how Halley correctly called the return of the comet named for him. It's how we keep tabs on worrisome bits of rock that come rather closer to the Earth than we'd like.

Tell us why that orbit implies that to you exactly, and we shall see.

Kepler's Laws:

1. The orbit of a planet is an ellipse with the Sun at one of the two foci.
2. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
3. The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

 

[dad]

Do you normally not trust experts? If your doctor tells you that you are sick and need medicine, do you consider that "blind faith in man"?

When your doctor says he got back from the far side of the universe we can ask him.

 

[dcarrera]

False! You take time...time exists here on and near earth you know..and space here...that is the base line for the triangulation. We know time exists here...not at the star though. You cannot extend a time and space line to the star!

What is your proposed explanation for parallax? How does parallax even assume anything about time at the star?

 

[dad]

Sure. Here is the paper with the Planck results.

http://arxiv.org/pdf/1303.5062v1.pdf

My favorite figure is figure 19 on page 27, which I include here:

The vertical axis is the power spectrum and the horizontal axis is the angular scale. For example, you can see that most features on the CMB are around 1 degree in size. In this figure, the green curve is the prediction of the LCDM model and the red points are the data from the Planck satellite including their 1-sigma error bars. I think that the fit is impressive, but I would be interested to see the same plot using the creationist model.

OK so we see light or the background radiation a certain way. We get it. Now...show why that fits a big bang exactly.

 

[dad]

What is your proposed explanation for parallax? How does parallax even assume anything about time at the star?

I propose that time is built into the distance measures. Therefore unless time existed there at the star as well as here, the distances are garbage.

 

[dcarrera]

When your doctor says he got back from the far side of the universe we can ask him.

Why are you evading my question? I am asking a legitimate question, and your evasion just tells me that you don't actually care about what other people have to say. I asked whether you reject you consider it "blind faith in man" when your doctor tells you that you are sick. This is a legitimate question. Does your religion make you reject the entire notion of expertise in a field?