solar system

[scope potato]

I hope this doesn't sound too silly. After doing some reading, I understand what the ecliptic is . After reading it's definition does that mean that the sun and the planets all line up on the same flat plane?I've always wondered this and remember see.ing it depicted that was in texbooks and thought it was just a nice neat way of showing the layout of the solar system.Could someone elaborate on the subject. Jerry

[gnhuftalen]

For the most part. Neptune is a little weird and Pluo is way off, part of why it was demoted...Sorry, Jerry. the second part of this post must have been lost when I hit 'enter' as my keybord/mouse is kludgy and edits without permission...what I had planned to say, "For a more cogent answer about planetary formation, perhaps Bob M or Pete P will see this and respond." I do see that Bob M (rotorhead) did respond...thanks, Bob! thanks for the "edit" button, I don't feel so dumb.

[Rotorhead]

Jerry, the explanation of the ecliptic can be as simple or as complex as you wish. Basically, the entire solar system formed from one large spinning disc called the protoplanetary disc, with the sun sucking up most of the material in the middle and the planets and other leftovers forming from the outer portions of the disc. Thus, in a perfect world, the planets would all orbit in line with the sun's equator, all of the planets would spin in the same direction as the sun, with no tilt to their polar axes, and all the moons of the planets would orbit in the same direction around their planets in line with the sun's equator. In such a system, there would be an eclipse of the sun at every new moon, and an eclipse of the moon two weeks later. Hence the name 'ecliptic' - we only get eclipses when the moon crosses the plane at exactly the new or full phases. In fact, the solar system as it evolved over the past few billion years was a messy place with collisions, near misses, orbital migrations, etc, which stirred the perfect world up a bit, and nowadays all of the planets (except the earth) and the various moons are somewhat off the ecliptic, and wander above, below, and across it at various times, generally averaging out their movements to either side of the ecliptic over a given period of time. Since, from the earthbound perspective of the ancient astronomers, the sun appears to follow the ecliptic, even today the ecliptic is defined as the orbital plane of the earth, which is why we are always exactly on the plane of the ecliptic - the final holdover from the geocentric worldview . The devil is in the details, and it gets very complicated when the movements of individual bodies within the solar system are viewed in relation to the ecliptic, so leave it at the basic level unless you want to get a headache.

[scope potato]

Rotorhead, thanks for that detailed description of the orbits of planets in the solar system. I guess just like the pictoral rendition in a text it could only happen is a perfect world. Be assured if I knew how it was I wouldn't of asked . Now that I've asked I'll leave things as they are and accept what you described. I guess this is why tracking down celestial objects is so difficult. Bob and George, thank you. jerry

[Rotorhead]

There is no such thing as a foolish question in astronomy. I'm pretty good at terrestrial maps and charts (a handy thing in the Marine Corps ) but I initially found celestial charts to be as alien as anything I've ever seen devised by humans. Maybe it has to do with the same mountain being in the same place from month to month, while the sky changes constantly.... The moon rises in a different spot every night, and the constellations as they come up look very different from when they go down. It takes some time to get comfortable in such a fluid situation. But I encourage you and others to ask, ask, ask. Sometimes it will ignite a furious debate, sometimes it will get you a dry textbook summary (most of my answers, for instance ). Unless you studied celestial navigation in the Navy, my guess is that the sky is just as full of questions for you as it was for me. But I asked a lot of questions when I joined the club, after nearly two years of owning a telescope and hardly finding anything in the sky. And everyone was generous with answers, as they still are. So ask away!

[scope potato]

Thank you Rotorhead. You and others have put me quite at ease because the goal of all this is to be educated, I am going to take full advantage of it as a matter of fact I have another. I've been told that it's all ways the same side of the moon that all ways faces us (the earth). Does that mean the moon has no rotation??If it is true, is there an explanation or theory why it is so?
Jerry hey bruce is the check in the mail??????????????????????????????????????

[bruce d]

No check yet?

Interesting point Bob, it never occured to me that we would have eclipses every month if everything wer right on the eliptic

[scope potato]

Oh hi #1 from what you just described about an eclipse each day , wouldn't that be true for venus and mercury any time they pass between us and the sun?? Jerry Yes it came postage due

[bruce d]

Yes another good point Jerry, we would have Mercury and Venus transits on a regular basis!

[Rotorhead]

Think about the moon and its rotation. If the moon orbited but never rotated on its axis, we would get to see one side of the moon during half of its orbit, and the other side during the other half.... Since the moon is tidally locked to the earth, the moon actually rotates once each lunar month, so that it always shows us the same face. And in fact, since the moon wobbles slightly and its orbit allows us to peak over the top, under the bottom, and around the corners at various times, so that in about a 30-year cycle (I think - I'm pulling this out of my head) we see just about 60% of the moon's surface. BTW, all of the Galilean moons, plus Titan and Triton are all tidally locked to their host planets.

[gnhuftalen]

Wow. You gotta love this club! I learn so much from my fellow ASSNE members...

[scope potato]

Well for once in my life I have stimulated some intelligent thinking and conversation This hobby and this group really have a good thing going and as George said I "fit" right in.I feel like i have so much to learn but then again I think I have so much to give. Jerry

[bruce d]

Thank you Jerry, we all learn from each other- but mostly we learn from Bob M

[scope potato]

Another question I just though of Do all the planets travel at a constant speed? Do they all travel at the same speed??? I do know that because of their orbits they all take different times to orbit the sun, but I'm curious about if they all travel at the same speed . Jerry

[Rotorhead]

Thanks for the plug, Bruce, but I think that I answer these questions simply because I'm the retired guy and can get to them before you poor working slobs do. I am fortunate to have taken several college-level astronomy courses, and I have textbooks on my bookshelves about a number of subjects, including astronomy, just for occasional perusal. I've always been comfortable with the cosmic concepts as long as nobody talks about equations. I am severely allergic to math.... But insofar as observational and astrophotographical astronomy are concerned, I've learned a wealth of things from members of this club who have no need to be shy where their knowledge is concerned. It is world class. I have only owned a real telescope since 2003, and still have much to learn from our more seasoned observers.

Jerry, back to your question about orbital speed. Again, the answer can be simple or complicated, depending on how deeply you reach. The simple answer is that all the planets orbit at different speeds. Orbital speed depends on two variables: distance from the main body, and the masses of both the orbiting body and the main body. Then it gets complicated and involves arithmetic, so I bow out of this part of the discussion.

However, remember that no object truly orbits another. They orbit their common center of gravity (more specifically, their common center of mass) and since gravity is universal, even the ISS tugs on the earth and pulls it very slightly out of place constantly during each orbit. ALL of the planets tug on the sun, and some (think Jupiter and Saturn) have considerable effect on the sun's position. Which, of course, affects the orbits of everything else orbiting the sun. And the planets and their moons tug on each other and perturb each other's orbits, which is how the position of Neptune was inferred even before the planet was found. And, since planets orbit in ellipses, not circles, the speed of each planet actually varies during each orbit of the sun, depending on the particular spot where it is on the ellipse. I could go on, but you get the picture. This complexity is why, in the early days of the space program, it took a roomful of very bright people with slide rules to calculate the slightest change in the orbits or trajectories of the various satellites (remember Apollo 13?). I honestly don't know how they did it. But then again, I get a headache balancing my checkbook.

[scope potato]

Bob, quite an interesting answer. I understand what you mean by mass of an object and I understand how it can interelate with anything under an object's influence. So to put it into my own words The speed of the planets are affected by the other planets moons and the sun. Dependant upon the proximity of other objects at that time in a particular orbit and the effects of gravity will determin the speed of the object, at a specific time and place??? Does that sound like I'm in the ball park?? This is all coming back to me now I had a couple of courses in nuclear physics .thanks to UNCLE. Jerry

[scope potato]

Talk about complexity?? When I was in training for nuclear power one part of the training was to figure out the power level of the reactor when taking it on the line. As a lot of this stuff was new to everyone and there was no knowledge of the sub atomic particles that have been discovered. Back then for what we knew that is the size and shape of certain parameters What are the Chances this reaction will occur or how many of those will occure??? The whole formula for determining exactly what rod height the reactor would go self sustaining was based on probabilities. So to put it bluntly ,it was sorta like making a bet what would happen. Fortunatly for us, it works. Not only does that formula work, but it's pretty darn accurate. Jerry

[Rotorhead]

Jerry, I think I'm going to loan you one of my textbooks...

Go back to the simple solar system model. Each planet has a speed based solely on the momentum needed to keep it in orbit, and that is affected only by the mass of the sun, the mass of the planet, and the distance from the center of the sun to the center of the planet. If the planet went any slower, it would spiral into the sun. Any faster, it would leave the solar system. The complexity comes when we look at the perturbations (which are usually fairly small) caused by the interaction of all the moving parts of the solar system.

[gnhuftalen]

Bob, I am currently reading Alan Hirshfeld's "Parallax." In reading about the various models of the solar system I am at the point where the heliocentric model becomes accepted and how Newton discovers that the planets' orbits are eliptical, rather than the circular classical model. My question is--I have not yet gotten to a point where it is explained WHY the planetary orbits are eliptical. Why are they? If the sun is a sphere, and the protoplanetary disc formed at its equator--where the sun's gravity is strongest--then why aren't the orbits circular? Is the shape of the orbits influenced by the other planets or other bodies in the solar system, like the asteroid belt or Kuiper Belt? Why eliptical, rather than circular orbits, and why some odd orbits, such as Neptune and Pluto?

[Rotorhead]

I'll have to talk to Al about getting certified as an adjunct professor so I can start charging for my instruction...

Believe it or not, George, but my textbooks say nothing about WHY elliptical orbits are the norm. They just say it is so. I suspect, however, that it is the residual effect of most objects in the solar system not being in the places where they originally formed. For instance, the typical computer models of the protoplanetary disc all agree that the outer portions of the disc did not have sufficient material to form Jupiter, let alone TWO gas giants and two ice giants. So they must have formed in the inner disc near where we are now. Man, THAT would be a solar eclipse to see, huh? (News flash - "Next week, there will be a Jovian eclipse of the sun. All week... Everywhere.") As the planets migrated to their current places - not a well-understood phenomenon in planetary theory - they would have had the 'wrong' orbital speed for the new region, sort of like the huge elliptical orbit (and occasional rocket motor braking maneuvers) of the Mercury Messenger mission, intended to lose orbital momentum gradually before the satellite settles into it's permanent orbit. That leaves quite a bit of speeding up and slowing down in the residual orbit, I'm sure, which is why we have perigees and apogees in every orbit of every object that we know of. But that is just my idea, the texts just don't say. Eventually, the ellipses become nearly circular, as are most of the current orbits, but still enough of an ellipse that the early Copernican model failed the simple test of predicting planetary positions - a major stumbling block to being able to 'prove' that it was correct.

BTW, it was Kepler who postulated the elliptical character of orbits, based on Tycho Brahe's excellent and extensive observations - all done without the aid of a telescope. Kepler's work on Mars' orbit (it took YEARS with pencil and paper to crunch Brahe's data to calculate one planet's orbit!) was the first proof of the correctness of Copernican theory.

Pluto's orbit was Prosecution Exhibit #1 in the case for demoting it. But that will be the subject of next week's class....

Yeah, I love this stuff.

[scope potato]

Bob , George, I,m sure for every person you involve in this conversation you will have as many answers.By listening to what the two of you have dicussed I can'nt help but notice how similar the orbital dicussion is with the inner workings of the parts of an atom. The only thing I don't know if atoms have these eliptical orbits. Mind the both of you I don't have the education that you have but I think I have a good understanding of some things as long as I reason them out. My personal belief is that basically there are two forces at work. Gratvity and Momentum in the form of potential energy.These two forces are at constant odds with each other. I also feel that a third force is at work here due to my own reasoning that affects the other two, for lack of of a definition let's call them gyroscopic forces. The way I see it the planets go around the sun the e moons go arounrd the planets and while this is all happening the whole thing is traveling in unison through space.I believe it's these gyroscopic forces that first work with one of the other forces then switch to the other at some point in the orbit is the reason for the eliptical orbit. Tthis is not to discredit what you or others have said but it is with my own reasoning that I have come up with this. Besides it is through expressing opinions that ideas are born. Jerry (ex poor working slob")

[petep]

Prof. Magnuson's answer is a pretty one Jerry. I think that you're alluding to perturbations - the unsettling gravitational effect of planets upon one another. And that enters the equation too.

Pete

[scope potato]

Pete that is exactly one of the points I am trying to make. As I said there are more than two forces that come into play and as far as I'm concerned we're all right. Right wrong or indiferent,the positive thing that is going on is an exchange of ideas to review or debate in an inteligent manner . By sharing this exchange of Ideas new ways of looking at the same thing could lead to a whole new understanding of why things react the way they do. Edison was once asked what of all the failed attemps to find the element that would work for his incandescent lamp . he replied"those were not failures they were discoveries of things that didn't work". Jerry

[petep]

Right wrong or indiferent,the positive thing that is going on is an exchange of ideas to review or debate in an inteligent manner . By sharing this exchange of Ideas new ways of looking at the same thing could lead to a whole new understanding of why things react the way they do.

Uhhh, Jerry, I'm not sure that the scientific method is associated with debate. I believe that what Bob said is accepted theory, and I was simply adding something that he'd left out.

Pete

[scope potato]

Pete, Bob, and george, my apologies I stand corrected Some times I get carried away. Jerry