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The solar system 90 degrees to milky way

  1. Jul 5, 2013 #1
    I live at 4000 feet above sea level and list night I saw some shooting stars, one real big one coming from the south so i thought I would star-gaze awhile and see if more meteors would come my way, no more came and after awhile I was admiring how well I could see the milky way and then I realized it was running North to South and something inside just jumped out and said this is not right, so I run the model of earth and galaxy in my head like 3 times to make sure I am seeing this right, now I am positive That this is not right, so I go make a Google search and really not that much came up on this subject , besides that it is a mystery to why this is, so Then I start wondering is this common? are other solar systems at odd angles to the galaxy like this or is it some kind off anomaly, and I am 43 years old and I have never seen the solar system portrayed in this manner, its always shown as on the same plane as the galaxy, what the heck. I have tried to find out about other solar systems and the way they are oriented to the milky way, but I cant find anything, astronomers are finding all kinds of new planets in the news all the time but no news of how the angle of the orbits are.
    I would really like to know.
  2. jcsd
  3. Jul 5, 2013 #2


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    Hi, jeritude. Welcome to PF!

    You're right, although not precisely so. The plane in which Earth orbits the Sun(aka the ecliptic) is indeed inclined about 60 degrees, roughly towards the direction of orbital motion around the galactic centre.
    The angle the band of the Milky Way makes with the horizon will somewhat differ from that value due to the axis of Earth's rotation being inclined to the plane of it's orbit, so it might look closer to, but not quite, 90 degs.

    You can see it modelled in any good planetarium software(e.g.: http://www.shatters.net/celestia/ - the software is free. Try fidling with the display options in "render"->"view options" section. Turning on e.g., orbits and galactic coordinate grid should help you orient yourself).

    The actual value of the angle of inclination in a stellar system is a pretty much random occurence. On a local scale of the system, all planets end up revolving around the star in almost the same plane due to the way the dynamics of a collapsing cloud of primordial gas work. Similar reason is why most stars lie in the same plane in the Galaxy. However, between these two scales, there is little overlap in dynamic influences - the individual stellar systems have inclinations independent of the galactic plane.

    This randomness is a major obstacle in some astronomical observations. For example, only if the orbit of an exoplanet lies in a plane that is almost exactly "edge on" towards the direction to the observer(i.e., us) can a transit in front of the stellar disc be observed, and the planet detected.

    Finally, if you know what the key words you should be looking for are(i.e., ecliptic; inclination; galactic plane), you'll find much more about it. For example, it's mentioned in the wiki article:
    Last edited: Jul 5, 2013
  4. Jul 5, 2013 #3


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    Hi Jeri, and Bandersnatch.
    That was a nice clear description. Maybe the links should be in our AstroCosmo bibliography thread.You could add them. It is a sticky or "pinned" thread in the main Astro forum.

    Jeri Ill try to say more about that 60 degree tilt. You could tell us what latitude you live at because that will affect the tilt you actually see.
    I live at 37 North latitude and there is a time of year when in the evening when the stars are out the milky way nearly coincides with the horizon
    I believe if I lived at 30 North then, because of that 60 degree tilt then the plane of galaxy would EXACTLY coincide with my horizon once a day

    but for me to enjoy that it would need to happen when it was dark, for example say at midnight around 1 of April or an hour earlier around April 15 or two hours earlier around May 1. you know how it goes. These are just approximate times, I don't remember the exact numbers.

    A way to picture it in your mind is to imagine being above plane of galaxy looking down at it rotating CLOCKWISE so that is "up", and then you descend down and STAND of the plane of the galaxy near where the solar system is, FACING in the direction things are rotating. And you look at the plane of the solar system and you see that it is tilted IN THE DIRECTION that it is going. The solar system "north pole" axis is not pointing straight up, it is tilted roughly in a forwards direction leaning towards where the solar system is sailing in its voyage around the center of the galaxy

    But as B. indicated I think, planes and directions of rotation of planet systems seem RANDOM oriented with respect to plane of galaxy. If you are standing on plane of galaxy with the choice of "up" which I described then the galaxy is rotating CLOCKwise under you, at your feet. But if you crane your neck a little and look down on the tilted plane of the solar system, you see planets circling COUNTERclockwise. It's just how it is planet systems have no reason to conform with the much larger scale galaxy rotation pattern.

    At my latitude, I get to stand on the plane of the galaxy whenever the milky way is all around on my horizon, and then if I face roughly North (or a little East of N) I am facing in the direction that the sun is going with its planets. And the CENTER of the galaxy is on my right hand, to the East, or a little South of E) about 90 degrees from the direction I am facing.
    A distinctive constellation Scorpio marks that direction more of less. A fishhook curve of stars. More recognizable than its neighbor Sagitarius which is the official marker.
    I get to stand on the plane of the galaxy and orient myself that way for example at 10PM around 1 May, if I remember right. That would correspond to midnight on 1 April which is how I manage to remember the moment planar coincidence.

    Anyway, what is your latitude? (that seems to be the main thing that determines what tilt the milky way will seem to have at those times when it coincides most closely with your ground plane.)
    Last edited: Jul 5, 2013
  5. Jul 5, 2013 #4


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    It's worth imagining the distance scales here.

    If the solar system all the way out to Neptune (that is, all of the solar system that more or less sits nicely in the ecliptic - Pluto is weird) were the size of a pea, then the Milky Way galaxy would be about the size of Europe. Thus, the angle of the ecliptic can be thought of as an insignificant local perturbation against the overall flatness of the galaxy, no more significant than ripples on the ocean against the overall spherical shape of the earth.
  6. Jul 5, 2013 #5
    Marcus -33.0786° N, 116.6011° W
  7. Jul 5, 2013 #6


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    Thanks for responding! BTW I can't place it on the globe and I guess you might mean 116.6 East, not West, but in any case I will assume you are 33 degrees south of the equator, on SOME longitude maybe not 116 West. Then I would say that (doing the geometry in my head, and I could be wrong) the time of planar coincidence would be midnight on or around 1 October.

    You should imagine "up" differently because you are in S hemisphere. Picture your self ABOVE galactic plane with the galaxy below you rotating COUNTERclockwise. Face in the direction of rotation and drift down until you are standing smack on the galactic plane. The galactic center will be on your LEFT side. You can extend your left arm and point at it.

    Living where you do, this galactic plane you are standing on will correspond to your home ground plane at midnight 1 October. You will be facing NORTH (or a little west of North, like 20 degrees west of North) and that is the direction the sun is sailing

    And if you extend your left arm WEST (or a little south of West) it will be pointing at the CENTER of the galaxy, where you might see some of the stars of Scorpio, which marks the center. The ideal center is very near the Tip of the Tail of the scorpion.

    But if you don't like to stay up to midnight, you can go look at 10PM on 1 November. Then also the milkyway should be all around you along your horizon.

    BTW having it along horizon can make it hard to see because of city lights and hills and trees. So unless you are on a hill with a dark sky this is not practical stargazing advice I am giving you. It is more a thought experiment involving the coincidence of two planes: your ground plane and the plane of the galaxy.

    -33 degrees N is a nice latitude for this! That is 33 degrees South latitude
    If instead of 116.6 W long. you mean 116.6 E, then you'd be not very far from Perth, a bit to the south and east of Perth. You say elevation 4000 feet. It looks like a nice place to look at stars from.
    Last edited: Jul 5, 2013
  8. Jul 5, 2013 #7
    Thanks Marcus, Sorry for the confusion, I live in Julian California , USA 33.0786° N, 116.6011° W
    Last night the milky way was in the center of the sky directly over head, It it appeared to be going north south perfectly although it did have an appearance of a slight arch.
    Last edited: Jul 5, 2013
  9. Jul 6, 2013 #8


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    I see the minus sign (in your other post) in front of the 33 fooled me

    Basically the event I'm thinking of should occur 2 hours earlier per month and it happens at midnight around 1 April. We are 3 months later so coincidence of the two planes should happen at 6 PM (six hours before midnight).

    So if your ground plane coincided with the plane of the galaxy at 6 PM today
    then by midnight the earth should have rotated 90 degrees and the plane of galaxy should be 90 degrees perpendicular. the Milky way should, like you say, be running roughly north south down the middle of the sky. Roughly along the "meridian" as they say (the northsouth centerline of the sky.)
  10. Jul 13, 2013 #9
    1988AJ.....96.1967G Page 1968
    Title: Orbital planes of visual binary stars are randomly oriented - A statistical demonstration.
    Authors: Gillett, S. L.
    Journal: Astronomical Journal (ISSN 0004-6256), vol. 96, Dec. 1988, p. 1967-1970.

    1969SvA....13..303S Page 303
    Title: The Spatial Orientation of the Orbit Planes of Close Binary Stars.
    Authors: Shakhovskoi, N. M.
    Journal: Soviet Astronomy, Vol. 13, p.303

    Also random.

    Nothing on exoplanets, however.

    About the Solar System's misalignment with the Milky Way, it is typical.
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