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View Full Version : Why do all planets orbit in the same direction?

The_Radiation_Specialist
2005-Dec-21, 09:44 AM
I have a solar system stimulator software and i can see that all the planets orbit the sun Anticlockwise when looked from above north pole of the sun. Is it related to the turning of the sun or something else?

Ken G
2005-Dec-21, 10:13 AM
More correctly, the turning of the Sun and the orbits of the planets are all related to the same other thing-- angular momentum. The solar system formed from material that had some angular momentum, it's hard to avoid (every tried throwing a ball with no spin on it at all?). When gravity pulls it all together, the tiny angular momentum begins to make its presence felt. One way to think of this is, as a ball of gas contracts gravitationally, the characteristic speeds increase like the inverse of the square root of the characteristic size of the ball of gas. But an object soncerving angular momentum (as a contracting body will if its self-gravity is the only force around) has its characteristic rotation speed is linearly proportional to the inverse of the characteristic size. Thus the tendency to be rotating all the same way grows much faster than the tendency for the particles to move faster as the whole business contracts. At some point, the characteristic rotation speed equals the characteristic speeds of the particles, and the whole business must then be rotating around the same way. But to be orbiting and all going around the same way, they have to all be in a plane. So contracting balls of gas eventually reach a plane that is all going around the same way.

That would prevent further collapse, so you need other mechanisms that actually extract angular momentum so the collapse can continue (this is an ongoing area of research, not yet known). Magnetic fields are often invoked. But the bottom line is, you see the origin of the fact that the planets go around the same way, and are in the same plane-- they carry the "rotation" of the whole solar system (more so than does the Sun).

ArgoNavis
2005-Dec-21, 10:25 AM
I have a solar system stimulator software and i can see that all the planets orbit the sun Anticlockwise when looked from above north pole of the sun. Is it related to the turning of the sun or something else?

what solar system simulator software do you use?

The_Radiation_Specialist
2005-Dec-21, 10:56 AM
I use Sky View Cafe (www.skyviewcafe.com) ....the best way to say is that is a java applet...maybe saying software isnt a correct term for java applets?
But I think its great, it has many different tabs and the best part is that its free!

mickal555
2005-Dec-21, 02:30 PM
Simplfied: When the gas cloud that formed the sun and planets colapsed it started spinning, and(basicly) everything that orbits the center of the solar rovolves in the same direction today.

joeastronomy
2006-Mar-30, 09:58 PM
I just have a couple of questions for someone to help me out with. If there was a solar system that was discovered and it had 10 planets, 5 of which rotate clockwise and the others counter, what would happen. Would that work or would something happen. Next, Can we see the same constellations as people in south american, Argentine, and why or why not. Lastly, would it make sense if NASA planned to launch a spaceship to leave milkyway galaxy to take photos of galaxy from the outside? Thank you soo much.

_DRAGONLORD_
2006-Mar-30, 10:09 PM
There is no Up or down in space so diferent angles change the
way it looks when it rotates.

joeastronomy
2006-Mar-30, 10:11 PM
I just have a couple of questions for someone to help me out with. If there was a solar system that was discovered and it had 10 planets, 5 of which rotate clockwise and the others counter, what would happen. Would that work or would something happen. Next, Can we see the same constellations as people in south american, Argentine, and why or why not. Lastly, would it make sense if NASA planned to launch a spaceship to leave milkyway galaxy to take photos of galaxy from the outside? Thank you soo much.

AGN Fuel
2006-Mar-30, 10:38 PM
I just have a couple of questions for someone to help me out with. If there was a solar system that was discovered and it had 10 planets, 5 of which rotate clockwise and the others counter, what would happen. Would that work or would something happen.

This is overwhelmingly unlikely to ever occur, because the planets form over millions of years from a 'disc' of gas that revolves around the proto-star. Whatever the direction of revolution of the original disc, that will be the direction of revolution of the planets that form out of it.

Unless you are talking about the rotation of the planets on their axis, in which case it would work just fine. Venus, for example, rotates on its axis in a different direction to most of the rest of the planets.

Next, Can we see the same constellations as people in south american, Argentine, and why or why not.

Well, that depends really on where you are. I am in Australia for example, and would see the same constellations as people in South America. I assume that you are in the North American continent - you will see some of the same constellations - those near the 'celestial equator' such as Orion etc. However, because you are in the Northern hemisphere, you will see some constellations such as Ursa Major, Draconis, etc that they will not. Likewise, they will see some constellations (such as the Southern Cross, Centaurus etc) that you will not.

Why? Because the Earth is round and you cannot look through it!

Lastly, would it make sense if NASA planned to launch a spaceship to leave milkyway galaxy to take photos of galaxy from the outside? Thank you soo much.

Lovely idea, but a little impractical. The Milky Way is roughly 100,000 Light Years in diameter, so to get a snap shot of the whole thing, you would have to travel 'out' of the plane of the galaxy at near the speed of light (which we are nowhere near capable of doing!) for hundreds of thousands of years to get your photo of the whole galaxy.

(Edited to note: I didn't just do your homework for you, did I?)

antoniseb
2006-Mar-30, 10:44 PM
1. If there was a solar system that was discovered and it had 10 planets, 5 of which rotate clockwise and the others counter, what would happen. Would that work or would something happen.
2. Can we see the same constellations as people in south american, Argentine, and why or why not.
3. would it make sense if NASA planned to launch a spaceship to leave milkyway galaxy to take photos of galaxy from the outside? Thank you soo much.

Hi Joe, welcome to the BAUT forum.

I numbered your questions for easy reference. Here's some answers.
1. Probably such a system would have the inner planets orbiting in one direction and the outer planets orbiting the other way. Such a situation is unlikely but plausible if a star picked up a counter-rotating disk from another proto system.

2. People in the temperate zones in the North (e.g. US & Europe) can see some of the same constellations as people in the temperate South. Orion for example.

3. No. Such a mission would take too long (millions of years), and be very expensive to build.

Jeff Root
2006-Mar-30, 10:52 PM
If there was a solar system that was dis*covered and it had
10 planets, 5 of which rotate clockwise and the others counter,
what would happen. Would that work or would something happen.
Nothing would happen. It wouldn't even be a problem for the
Qwertzes and Poiuyts living on the planets.

Next, Can we see the same constellations as people in South
America, Argentine, and why or why not.
I'd prefer if you could answer this question yourself, before
someone else does. Do you have a globe? (If not, tell someone
you want one for your birthday! Every home should have a globe!)

Find your location on the globe. What parts of the room you are
in could a miniature version of yourself see from that location?
What parts of the room could a miniature person in Argentina see?

Rotate your globbe around the polar axis. Notice what parts of
the room your miniature could see as the globe rotates. What
parts of the room could a miniature person in Argentina see?

Lastly, would it make sense if NASA planned to launch a spaceship
to leave milkyway galaxy to take photos of galaxy from the outside?
No, it wouldn't. Nomatter how much money they had. Infinite
money, even.

Can you tell me why it wouldn't make sense? I bet you can!

PS Thanks a lot AGN! :P

-- Jeff, in Minneapolis

AGN Fuel
2006-Mar-30, 10:56 PM
PS Thanks a lot AGN! :P

-- Jeff, in Minneapolis

D'OHHH!

antoniseb
2006-Mar-30, 11:07 PM
I have merged the two threads where joeastronomy posted his identical queries.
Joe, you should only post something like this once.

Lord Jubjub
2006-Mar-30, 11:40 PM
Wasn't there a recent discovery of a gas cloud that had counter-rotating layers?

antoniseb
2006-Mar-30, 11:59 PM
Wasn't there a recent discovery of a gas cloud that had counter-rotating layers?

Yes, which is why I mention that counter rotating planets are possible.

joeastronomy
2006-Mar-31, 08:42 AM
Thank you all, I appreciate all your help. And no you didnt help me do my homework. Those were qustions my teacher asked and didnt get to in lecture the other day and I wanted to see if what I had was correct or along the same lines.

Oh and Mr. Root, don't take this the wrong way but don't treat people like less and talk down to them like you did in your reply. I understand how to do it and had my answers already, but sometimes its nice to hear what some people that are more educated on the subject have to say. And when I was asking that question it was more about whether we see a great number of different constellations or would it be just a few. Sorry I guess I should have made myself more clear.

Also sorry for the double posts. I was under a heading that dealt with my question somewhat but after I posted I looked at the dates of the other postings and they were from 2005 and older. So I didn't know if anyone would see it. Well, again I thank you all for your help and quick responses.

Last questions here. Ok im going to give my answer to the question so then you can tell me if I am right or way off.

Question Now, say there is a solar system that has 4 jovian planets in its inner solar system and seven small planets in its outer solar system. Would these properties, in the light of our theory of the solar system formation, be reasonable or surprising?

My answer: I pretty much said that it wouldnt be possible becuase jovian planets are mainly composed of gases and ice and if they were in the inner solar system near the sun then they would condense because of the higher temperature and therefore they would condense into metals and rock to form a terrestrial planet.

My second question is, would it be possible to see Venus shining bright on the meridian at midnight?
Sorry If this is a dumb question for all of you, but I guess I just ask you to spare me the sarcasm. Thank you again sooo much.

Thats just a quick summery of my answer but let me know if I am wrong. Thank you and I greatly appreciate your help. Sorry this post is so long.

Jens
2006-Mar-31, 09:20 AM
Oh and Mr. Root, don't take this the wrong way but don't treat people like less and talk down to them like you did in your reply. I understand how to do it and had my answers already, but sometimes its nice to hear what some people that are more educated on the subject have to say. And when I was asking that question it was more about whether we see a great number of different constellations or would it be just a few. Sorry I guess I should have made myself more clear.

Yes, you probably should have made yourself more clear, because I thought Jeff's response was a very good one. He was merely giving you help on how to think through the problem, and to be honest, it might have offended you for some reason, but I think that in general, too many teachers give straight answers to problems rather than teaching how to solve them, and even if you didn't want it yourself, you should also remember that other people are reading this forum, and might have the same questions. BTW, I'm long past my student years, but I still do what Jeff suggested at times: get out the globe and spin it around to see what happens. I think it's very solid general advice for anybody, and don't think it should be seen as condescending.

formulaterp
2006-Mar-31, 03:51 PM
My second question is, would it be possible to see Venus shining bright on the meridian at midnight?

No, you would not be able to see Venus at midnight. Venus is an "inferior" planet, meaning that it is closer to the Sun than the Earth. At midnight, an observer would be facing away from the Sun and Venus would be on the other side of the planet. Generally speaking, one can only see Venus in the early mornings or late evening wiht the naked eye. Venus can also be seen during the daytime with proper filters to block out the glare of the Sun (or during an eclipse) or as it transits across the face of the Sun.

antoniseb
2006-Mar-31, 03:59 PM
No, you would not be able to see Venus at midnight.
I disagree. You can see Venus at midnight under special circumstances. Note that you have to be North of the Arctic Circle, or South of the Antarctic Circle for this to happen. This is an important matter to people who were trying to figure out where Rowling thought Hogwarts Castle is. Personally, I think that Potter just had Venus and Jupiter confused, and Rowling was just showing him to be falible.

joeastronomy
2006-Mar-31, 04:30 PM
Yes I do think it was a good description but just the way it sounded when I read it, it seems like he was try to be sarcastic and he felt it was a stupid question. And when someone new comes to your forum you should probably not act like that towards them because they may not come back, but who knows if you guys care. And yes it is good to think through problems but you guys just assumed that I had no clue and was just asking these questions when in all reality I had already thought through them and had written out. But oh well. I still thank you for your help.

Kaptain K
2006-Apr-01, 02:24 AM
I disagree. You can see Venus at midnight under special circumstances. Note that you have to be North of the Arctic Circle, or South of the Antarctic Circle for this to happen.
While your answer is correct, as stated. the original question was:

My second question is, would it be possible to see Venus shining bright on the meridian at midnight?
Note emphasis!

The answer, in this case is no!

Kaptain K
2006-Apr-01, 02:35 AM
Question Now, say there is a solar system that has 4 jovian planets in its inner solar system and seven small planets in its outer solar system. Would these properties, in the light of our theory of the solar system formation, be reasonable or surprising?
Very surprising! Current theory have gas giants forming in the cooler region of the protoplanetary disk. They can and do migrate inward (do an internet search for "hot jupiters"). Rocky planets form in the inner region of the disk, where radiation and the solar wind blow away the lighter gases. When the gas giants migrate inward, they fling any smaller planets out of the system (or into the star).

JMV
2006-Apr-01, 03:19 AM
While your answer is correct, as stated. the original question was:

Note emphasis!

The answer, in this case is no!
Why not?

What if a Venus conjunction were to occur at June or July so that it will not transit the Sun but goes past it from above the ecliptica, and that you are observing it from a point near the arctic circle where Venus is seen above the horizon and the Sun just below? Wouldn't Venus be really low above the horizon straight at north on the meridian at midnight?

Ok, it probably wouldn't be shining bright because atmosphere refracts sunlight from below the horizon lighting up the sky somewhat.

I took a screencap of Celestia depicting the possible conjunction. Earth's axis points the wrong way in the pic because it's at October, but imagine the same conjunction at June. Would it be possible?

Gillianren
2006-Apr-01, 04:02 AM
Yes I do think it was a good description but just the way it sounded when I read it, it seems like he was try to be sarcastic and he felt it was a stupid question. And when someone new comes to your forum you should probably not act like that towards them because they may not come back, but who knows if you guys care. And yes it is good to think through problems but you guys just assumed that I had no clue and was just asking these questions when in all reality I had already thought through them and had written out. But oh well. I still thank you for your help.

But how were we supposed to know that you already had answers? Generally, when people ask questions, it's because they don't know something, and you were being taught how to figure it out, which is (I agree) very important.

As to how we act to new people, it generally depends on how they act to us, so there's no across-the-board (no pun intended!) way that we treat them. However, I will say that many people around here get irked when it feels like we're doing someone's homework for them--or we're being asked questions with obvious answers, which--to me, at least--the constellations question was.