I Orientation of the Earth, Sun and Solar System in the Milky Way

Bandersnatch

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I am assuming since the earth is near galactic plane (as illustrated) at the time of summer solstice, then the axial tilt of the earth would be in the direction of the sun and not to the galactic north.
Ah. You're right. Well spotted. It does look like it's pointing in the wrong direction, and should indeed be deflected towards the reader rather than in the plane of the picture.
Maybe @fizixfan will stop by and take a shot at correcting it. Although I imagine it might be difficult to render it clearly in two dimensions.
 
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I am assuming since the earth is near galactic plane (as illustrated) at the time of summer solstice, then the axial tilt of the earth would be in the direction of the sun and not to the galactic north.
I've been following this thread since Loki sullivan started posting, but I've been unable to fully understand what's being said. This may not answer your question, but the Earth's Axis of Rotation is tilted "away" from the Sun in the Winter, which is why it gets colder in the Northern Hemisphere during winter (you probably already know that), and tilted "toward" the Sun in the Northern Hemisphere in the Summer. The Earth is also situated between the Sun and the Galactic Center in the summer (Sun - Earth - Galactic Center). That's why we have such great viewing of the Milky Way in the summer months - because the Sun isn't in the way at night and we're looking toward the Galactic Center. In winter the Sun is between the Earth and Galactic Center (Earth-Sun-Galactic Center), so no viewing of the Milky Way in Winter from the NH.

The Earth, in a physical sense, is about 50 light years north of the Galactic Equator, so change in position of 186 million miles from over the course of a year isn't going to change our position with respect to the Galactic Plane. What does change is our point of view, since we are on a tilted, spinning sphere orbiting the sun.

The axial tilt of the earth does not vary relative to the Galactic North on a seasonal basis or even during a human lifetime - although it does precess (Google that term if necessary). But for the purposes of this discussion let's just say the North Celestial Pole (Earth's Axis of Rotation) and the North Galactic Pole (Milky Way's Axis of Rotation) do not vary. The angle between the NCP and NGP is 62.9°, although this can only be determined using spherical trigonometry, since the Celestial Equator, Ecliptic Plane and Galactic Plane do not intersect at a single point. See Figures 2 and 3 in my original post. I'm including another crude drawing I did that may help. Words are really kind of hopeless in explaining three different celestial coordinate systems - which is why I prefer pictures.

drawings-orientation-of-earth-sun-solar-system-in-milky-way-crop-annotated copy.jpg


It might also help if you read all the posts in this thread, but especially, I would encourage you to go to a place where there are dark skies during the summer months and look up. I recently purchased a telescope for my camera, and have found some amateur astrophotographers to hang out with. I would also recommend uploading Stellarium - a free planetarium program for your PC, and Skywatch for you mobile device.
 

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I've been following this thread since Loki sullivan started posting, but I've been unable to fully understand what's being said. This may not answer your question, but the Earth's Axis of Rotation is tilted "away" from the Sun in the Winter, which is why it gets colder in the Northern Hemisphere during winter (you probably already know that), and tilted "toward" the Sun in the Northern Hemisphere in the Summer. The Earth is also situated between the Sun and the Galactic Center in the summer (Sun - Earth - Galactic Center). That's why we have such great viewing of the Milky Way in the summer months - because the Sun isn't in the way at night and we're looking toward the Galactic Center. In winter the Sun is between the Earth and Galactic Center (Earth-Sun-Galactic Center), so no viewing of the Milky Way in Winter from the NH.

The Earth, in a physical sense, is about 50 light years north of the Galactic Equator, so change in position of 186 million miles from over the course of a year isn't going to change our position with respect to the Galactic Plane. What does change is our point of view, since we are on a tilted, spinning sphere orbiting the sun.

The axial tilt of the earth does not vary relative to the Galactic North on a seasonal basis or even during a human lifetime - although it does precess (Google that term if necessary). But for the purposes of this discussion let's just say the North Celestial Pole (Earth's Axis of Rotation) and the North Galactic Pole (Milky Way's Axis of Rotation) do not vary. The angle between the NCP and NGP is 62.9°, although this can only be determined using spherical trigonometry, since the Celestial Equator, Ecliptic Plane and Galactic Plane do not intersect at a single point. See Figures 2 and 3 in my original post. I'm including another crude drawing I did that may help. Words are really kind of hopeless in explaining three different celestial coordinate systems - which is why I prefer pictures.

View attachment 227104

It might also help if you read all the posts in this thread, but especially, I would encourage you to go to a place where there are dark skies during the summer months and look up. I recently purchased a telescope for my camera, and have found some amateur astrophotographers to hang out with. I would also recommend uploading Stellarium - a free planetarium program for your PC, and Skywatch for you mobile device.
Let me first say, thank you for sharing your work. I have learned much from your illustrations. As far as my inquiry, I hope you understand I am not criticizing your work but seeking clarification for my own understanding. I DO understand the axial tilt of the earth and its affect on seasonality. My question was referring to the direction of axial tilt of the earth. In the illustration, the angle of the earth axis in relation to galactic plane is apparent, but the axial tilt direction appears to be towards the sun when near the winter solstice. If I am understanding that the northern hemisphere is shown to the left, then wouldn’t the direction of axial tilt be away from the sun at winter solstice? It may just be a misinterpretation due to the nature of 2D renderings, so I ask for clarification for my own understanding.
 
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Let me first say, thank you for sharing your work. I have learned much from your illustrations. As far as my inquiry, I hope you understand I am not criticizing your work but seeking clarification for my own understanding. I DO understand the axial tilt of the earth and its affect on seasonality. My question was referring to the direction of axial tilt of the earth. In the illustration, the angle of the earth axis in relation to galactic plane is apparent, but the axial tilt direction appears to be towards the sun when near the winter solstice. If I am understanding that the northern hemisphere is shown to the left, then wouldn’t the direction of axial tilt be away from the sun at winter solstice? It may just be a misinterpretation due to the nature of 2D renderings, so I ask for clarification for my own understanding.
It's the nature of the 2D rendering, I'm afraid.
 
Looking at the Sun's direction of travel arrow on fizixfan's 'Motion of Earth & Sun around the Milky Way' diagram, does this mean then that the solar system is orbiting the Galaxy in a clockwise direction? Also, which hemisphere of Earth's is (mostly?) facing the direction the solar system is taking during its orbit round the galactic disc? North or South? Or do they each take turns during the course of a terrestrial year? I can't quite put it all together it somehow.
You'll be interested to know that, since the Earth's equator is inclined so steeply (60.2 degrees) to the plane of the Milky Way, that there are features of the Milky Way, such as the Galactic Center and Galactic Bulge, that can only be seen from the Northern Hemisphere, and features such as the Coalsack Nebula and the small and large Magellanic Clouds, that can only be seen from the Southern Hemisphere!
 

davenn

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that there are features of the Milky Way, such as the Galactic Center and Galactic Bulge, that can only be seen from the Northern Hemisphere
you sure about that ? :wink:

the galactic centre is in Sagittarius which comes well above the horizon in the southern hemisphere.
In fact at this time of the year, it passes right overhead
Maybe you take a trip "down under" one day and I and some other Australian astronomers will treat you to the delights of the southern sky


Dave
 
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Obviously I'm mistaken - Thanks for letting me know! I guess I'm not as familiar with the southern hemisphere as I'd like to be!
 

Janus

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You'll be interested to know that, since the Earth's equator is inclined so steeply (60.2 degrees) to the plane of the Milky Way, that there are features of the Milky Way, such as the Galactic Center and Galactic Bulge, that can only be seen from the Northern Hemisphere, and features such as the Coalsack Nebula and the small and large Magellanic Clouds, that can only be seen from the Southern Hemisphere!
Here's the relationship between the Celestial Equator, Galactic Equator, and Ecliptic.
coords.jpg

The white grid are celestial coordinates and the light blue grid galactic coordinates.
Note that the Galactic Center is ~29 degrees South of the Celestial equator. This means that it is visible in the entire Southern Hemisphere and not visible for points above ~61 degrees North Latitude. The ecliptic crosses the Galactic equator ~6.5 degrees from the Galactic center and the Celestial equator crosses the galactic equator 33 degrees from the galactic center along the galactic equator.
 

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Thanks, Janus - Are there any parts of the Milky Way that aren't observable from the Southern Hemisphere?
 

davenn

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Are there any parts of the Milky Way that aren't observable from the Southern Hemisphere?
Not really, as you can see from my pic. you can see it from one thin end on the left, through the centre and out to the thin end on the right side

What we don't see from the southern hemisphere are the constellations that are well away from the galactic plane ... ie. close to the north celestial pole

Ursa Major and minor, Cassiopeia, Draco, Cepheus, Hercules ... to name a few


Dave
 
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Hello

Thanks for all the posts. I would like to ask for some clarifications, if possible.
Here some images:
1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg

So, from Europe during summer, if I look at SagittA, the solar system is moving toward left (as do all the spiral arms). So, if I take a view-angle like in the second image, and clear my perception from local stars, voila, the "clouds" remain. They are in fact "curved", but we see them from inside the "tunnel", so to say. But, I can almost say that the curvature is perceivable, after I have trained my attention.

This is what I am uncertain of:

1. What do we really see in the left side of the Milky Way, are these light clouds the spiral arms?
2. If we move approx. toward Vega, how is that the SagittA and Vega are so close to each other in the sky? I suppose this is because Vega is so close, and galactic center is so so far away?

Thank you

Ovidiu
 

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Bandersnatch

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Hi, Ovidiu. Welcome to PF.

2. If we move approx. toward Vega, how is that the SagittA and Vega are so close to each other in the sky? I suppose this is because Vega is so close, and galactic center is so so far away?
They're roughly 70 degrees apart. Sgr A and the nearby Deneb are full 90 degrees apart. Deneb roughly points to the direction at a right angle with the direction towards the centre of the galaxy. 70 degrees is not that far from being half way through to the other side of the sky from Sgr A, so I'm not sure it counts as being close to each other.
If you're only looking at it through a planetarium software, then the separations on the sky may appear warped, especially if you zoom out. Try going out at night, and pointing towards both with each arm. Note the angle your arms make.

The radial distance to Vega vs Sgr A doesn't play any part in their angular separation. If you imagine looking at Vega, and then - in your mind - pushing it ten or a hundred times farther along the line of sight, it would not move from the same point in the sky. So distance can't play a role.

Btw, the difference between 90 degrees towards Deneb and 70 towards Vega comes from Sun's peculiar motion - i.e., its local velocity, unrelated to its orbital velocity.

Also, keep in mind these are not precise directions. Best to think of Cygnus/Lyra/Hercules as a 'roughly there' direction of motion, rather than pointing to any one star as the direction.
 
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Hello Bandersnatch

Thank you for your clarifications. Indeed, I perceive a difference, but seemed less than 70 degrees as I remember from last nights.
This is what I see, then? (just for orientation)

XPL1.jpg


xpl2.jpg


Looks like I have to wait until next clear night to look at this angle again, but I do remember this angle as 45 sort of, that's why it puzzled me.

Now, regarding my other question, about what we see.
I still cannot visualise this fact - so, we are moving toward Deneb-Vega
that means
- left of this area is just Perseus Arm? or?
- and in the right of Vega, then those "clouds" are in fact... 4-5-6 layers over layers?

I wonder if there is somewhere a scientifically correct image, using the perspective as in the image above?
I need to perceive-understand what I see, with arrows to show more reference points regarding the "spiral arms name", and also to show "the curvature" and the "layering" and the "Sun direction of movement"?

This is the best video I found, but it doesn't show the curvature of the spiral arms

Thank you
O.
 

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Bandersnatch

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I'm having a bit of a hard time understanding your pictures.
For example, in the first picture in your post #89, the approx 70 degree angle is between the directions that you marked with the wide red arrow towards the galactic centre, and the thin red arrow towards Vega. Not the much smaller angle between the two blue lines - which I'm not sure what are indicating.
The angle between the centre and Deneb should be a right angle.

Judging by how you've superimposed the image of the galactic arms onto the snapshot of the sky in the second picture in that post, it looks like you're making the mistake of not placing yourself inside the galaxy. You would not see all the arms (the entire galaxy) contained within the span of one night-sky (<180 degrees), since you are observing it from the inside. You'll see the galaxy all around you - including the parts of the sky below the horizon.

The band of the Milky Way is made of stars and dust contained mostly in the arms, but it is unlikely you'll be able to discern which arm you're seeing. In rough terms, if you look away from the galactic centre, you see the material in our arm, and in the Perseus arm. Looking towards the galactic centre, you'll see some combination of material in all the arms along your line of sight. There is no real way of separating material from one arm from another, just by eyeballing it, while sitting inside the galactic disc.

I'm still not sure we're not talking past each other, and if we do, then I apologize.
 
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Yes, we are on the same track :-) Thank you

The blue lines are just to show that what I perceived after some hours with "depths-wavey-rods-related" attention. The blue bubbles are what I perceived that may form curved spiral arms/structures of some sort. I know I am in the same plane as the arms :-)

The idea is that... loooking at the Milky Way... after some time, my visual perception can sense the difference between the light of the stars and the diffuse light from the far away arms. I see the clouds, but I also.. feel the curvature. It is because of the experiences with DMT and also, these exercises :-)

So, my experience is that I can perceive some curvature there, and my only working hypothesis is that... these bubbles-clouds of light seem to be curved following these ripples, as they are described below by some scientists. I cannot discern by analyzing light, but by feeling the curved energy-ripples.

This is how I do it - In order to activate this ultra-perception of depths, my energy enters in a hypersynchrony, and I get an amazing sensitivity. Our eyes are amazing, e.g. for some months I watched the sky only with one eye and trained my perception of "depths", to detect which objects are closer which are far, and in what order. So, maybe it is possible to do a some sort of triangulation even inside of one eye, by re-programming the perception. I heard about people who lose sight of one eye... the other eye compensate by naturally increase the sensitivity. But that's another discussion.

Maybe it looks impossible, but it is a matter of training and developing the sensitivity to light. And to be able to selectively use information only from some types of light receptors. Still, I need science to adjust my perception, it is not clear, because perhaps I use the rods-perception. So, the 3 dots I draw with blue is what I perceive. I thought they are arms, but after I discovered about the ripples and recently about density waves, I thought... this cannot be. I mean, whaaat? :-)
The arms are exactly in the position of the density waves, they say. And rods are very good at sensing densities, this is my current explanation of this perceptual vision.

So, the reason I am asking these things here is because I experience what you say it is impossible. :cool:
"There is no real way of separating material from one arm from another, just by eyeballing it, while sitting inside the galactic disc."
You know, maybe it is natural to the eye to do some sort of triangulation inside the retina. Maybe the distance is just some milimeters, but... the receptors can perceive a single photon, they say. I presume that in these high-energy-synchrony-experiences-DMT-like, my brain don't filter out these weak signals and they become conscious and I can play with them by ading them in a conscious way to the current perceptual vision. So, perhaps I use cones for close stars (and there is a very good perception of depths based on light differences), and for the "clouds" I use rods, and the "curvature" becomes available.

Thanks again
O.

thecorrugate - ripples.jpg

thecorrugate - .jpg
 

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Bandersnatch, here is an exercise for depths-perception:

I cover one eye, and look at the full moon through the window There are 3 layers ar least. One is the moon, the other is the reflection of the moon in the windows, the third is the image on the retina. They are over-imposed, but I can detect that the reflection in the window is veeery close compared to the distance where the physical moon is. And the retina is closer.

Then, I select mainly the light from the physical moon and look at it and merge with it. And voila, I get a clear perception of the physical moon. The halo in the window is also there, but I don't care about it, I select only the light from the moon to configure my experience. It is a selective use of samyama (or full absorption, as described in Yoga Sutra).

The brain is smart at composing 3D images by using these depths-mechanisms, it is just a matter of consciously choosing what the "feed" is :-)

O.

 
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It's possible to measure light and apply computation to figure out what is there, without a need to invoke perception or consciousness.
 
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Love this thread! Does anyone know the Sun's orbit inclination relative to the galactic plane? If it "wobbles" then this will vary, but there must be an average inclination?
 

sophiecentaur

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Love this thread! Does anyone know the Sun's orbit inclination relative to the galactic plane? If it "wobbles" then this will vary, but there must be an average inclination?
If you look at the Milky Way, on a clear, dark night, you see it as a diagonal line from Northish to Southish and that’s the plane of the Galaxy. OTOH the Moon, Sun and planets follow a broad East West band. That’s the plane of the ecliptic and the Sun’s axis is near normal to that plane. So they are different.
 

sophiecentaur

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I had a problem with the above thread. It refused to treat the quote as a quote and then wouldn’t let me edit, either.
Weird.
 

Janus

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Love this thread! Does anyone know the Sun's orbit inclination relative to the galactic plane? If it "wobbles" then this will vary, but there must be an average inclination?
There isn't really an orbital plane that the Sun strictly follows. It bobs up and down across the galactic plane several times per galactic orbit like this.
ZS5jb20vaW1hZ2VzL2kvMDAwLzAwNy81ODIvb3JpZ2luYWwvc3VuLW1vdmVtZW50LW1pbGt5LXdheS0xMDEyMjItMDIuanBn.jpg

If you average this out, it follows the galactic plane.
The bobbing up and down is due to the same type of effect you would get if you drilled a hole from North to South pole and dropped an object into it. It would travel back and forth through the hole in a harmonic motion.

With the Sun, as it gets above the galactic plane, there is more disk matter "below" it, and it is pulled back towards the plane. It overshoots, and passes below the plane, and now more disk matter is above it, pulling it again back towards the plane, which it overshoots... rinse and repeat.
 

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There isn't really an orbital plane that the Sun strictly follows. It bobs up and down across the galactic plane several times per galactic orbit like this.
View attachment 233686
If you average this out, it follows the galactic plane.
The bobbing up and down is due to the same type of effect you would get if you drilled a hole from North to South pole and dropped an object into it. It would travel back and forth through the hole in a harmonic motion.

With the Sun, as it gets above the galactic plane, there is more disk matter "below" it, and it is pulled back towards the plane. It overshoots, and passes below the plane, and now more disk matter is above it, pulling it again back towards the plane, which it overshoots... rinse and repeat.
Your description of the Sun's motion around the Milky Way is spot on, but the oft-used graphic (Medvedev 2007) used to illustrate it has a couple of errors. First, it shows the galaxy rotating clockwise (which is correct, with Galactic North as "up"), but the Sun is going in the wrong direction. It should be orbiting clockwise and not counterclockwise given the initial conditions of the diagram. The sinusoidal motion around the galaxy is also way out of scale. The Sun is about 26,000 light years from the center of the galaxy, and "bobs" above and below the galactic equator by a distance of about 250 light years in each direction. This means its northward and southward excursions above and below the galactic equator would only subtend and angle of about 0.55 degrees in each direction. It's hard to show these things to scale, but in my opinion, Medvedev got the direction of the sun's orbit backwards. Unfortunately, this diagram keeps being used, kind of like the erroneous "helical" model proposed by DJSadhu and now used and quoted by many. I've added a couple of diagrams of my own to try and make the Sun's orbit and motion easier to visualize.
Sun's Orbit around Milky Way (08Nov2018).jpg


Direction & Motion of Sun around Galaxy (08Nov2018).jpg


Motion of Sun around Milky Way Graph02 (08Nov2018).jpg
 

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phyzguy

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I keep pointing out that the sun's motion around the Milky Way is not an "orbit" in the sense that we usually think of it. It is not even a closed curve. Orbits in a central potential like the solar system are closed curves, but orbits in a potential well like the Milky Way's are typically not. Even if the Milky Way's potential were static in time the orbit would not be a closed curve, and it is definitely not static in time. So it is best to think of the sun's motion as an approximate orbit, where each path around the Milky Way is a different curve.
 
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While the galaxy does have an overall angular momentum, which the solar system goes with,
This is not like a planet orbiting a star, whose motion is highly predictable.
The solar system is part of a local cluster of stars, and the clusters are components of yet larger clusters.
Those clusters constitute the macro scale structures of spiral arms and a central bulge.
The dynamics of this for an individual star is completely unpredictable,
even to the point that a star could get ejected from the galaxy in a case of very bad luck.
 
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