Celestial plane orientation to the galactic core

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Discussion Overview

The discussion revolves around the orientation of the celestial plane in relation to the galactic core, exploring how different perspectives and definitions affect the understanding of this orientation. Participants examine diagrams and angles related to celestial and galactic coordinates, addressing the implications of these orientations in both theoretical and observational contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question the clarity of diagrams showing galactic orientation, suggesting that the direction of the core is not clearly defined in existing references.
  • Others argue that the question of whether the celestial plane is angled toward or away from the galactic core is inherently ambiguous, depending on the observer's perspective and the definitions used.
  • A participant points out that flipping diagrams could change the perceived direction of "toward" and "away," highlighting the subjective nature of the question.
  • Some participants reference specific angles, such as the 62.87 degrees between celestial north and galactic north, to argue that the plane is oriented more toward the galactic core.
  • There is a discussion about the definitions of the "celestial plane," with participants seeking clarification on whether it refers to the Earth's equator, the ecliptic plane, or another concept.
  • One participant emphasizes the need for accurate labeling in diagrams, noting that the orientation of the Earth's revolution around the Sun affects the interpretation of seasonal markers in the context of galactic orientation.
  • Another participant discusses the relationship between the ecliptic and galactic planes, suggesting that the inclination of these planes does not significantly alter the direction toward the galactic core.

Areas of Agreement / Disagreement

Participants express differing views on the clarity and meaning of the celestial plane's orientation to the galactic core. There is no consensus on how to define the question or the implications of the angles discussed, indicating ongoing debate and uncertainty.

Contextual Notes

Participants note limitations in the diagrams and definitions used, as well as the dependence on specific perspectives when discussing the orientation of the celestial plane relative to the galactic core. The discussion remains open-ended without definitive conclusions.

AutodiJack
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TL;DR
In relation to the galactic core, is the celestial plane tilted 23.4 toward or away?
Sorry if this is obvious, but I have studied all the images of galactic orientation online, but I need to be sure.

Diagram i made to help illustrate what I mean:

I believe it's towards, using this as a reference: https://www.physicsforums.com/threa...sun-and-solar-system-in-the-milky-way.888643/

But those diagrams don't show the direction of the core, only the poles. Unless I just don't get it.
 
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I believe it's a meaningless question since you can look at it as being either way, based on the on the direction you are looking at it from and what side of the galaxy the Earth is on. You have to define the geometry with precise terms, otherwise the answer of "is it angled toward or away" is "yes, it is"
 
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If you flipped your pictures upside down, don't towards and away switch places?
 
The answer is in the second picture in your reference. The 'Angle between celestial north and galactic north' is the angle between the Earth's axis and the line pointing from the Sun to the galactic center, and is 62.87 degrees, which means the plane is pointing more towards the core than away.
 
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phinds said:
I believe it's a meaningless question since you can look at it as being either way, based on the on the direction you are looking at it from and what side of the galaxy the Earth is on. You have to define the geometry with precise terms, otherwise the answer of "is it angled toward or away" is "yes, it is"
I'm not sure what you mean here, phinds. The celestial plane is tilted the same way all day and all year and only changes over very long time scales.
 
What is the "celestial plane"? Do you mean the plane of the Earth's equator, the plane of the ecliptic, or something else?
 
Drakkith said:
The answer is in the second picture in your reference. The 'Angle between celestial north and galactic north' is the angle between the Earth's axis and the line pointing from the Sun to the galactic center, and is 62.87 degrees, which means the plane is pointing more towards the core than away.
It is the second picture, agreed. But. The angle you're talking about is in a plane roughly parallel to the Sun-Galactic Centre direction. That is, the right ascension of the Galactic North is approx 13h, close to the direction of the autumnal equinox (to the right of the picture). In the picture it represents more the general slant of the plane of the ecliptic than that of the equatorial plane.

AutodiJack said:
Diagram i made to help illustrate what I mean:
As was said, the second is right. However you need to fix the labels. The Earth in that picture revolves around the Sun in the anti-clockwise direction, both by convention and by the depicted orientation w/r to the galaxy. So what follows the winter solstice should be the vernal (spring) equinox, not autumnal. Unless it's meant to represent the direction towards the equinox (but then there would be more to fix elsewhere), and not the time of the year.
Incidentally, the first picture would have Summer when it's labelled Winter, as it's the inclination of the equatorial plane that determines the seasons.

Back to the directions. You can find the equatorial coordinates of the major points of the galactic coordinate system on Wikipedia. The Galactic Centre is towards approx. RA 17h 45m, dec -29 deg. In both cases roughly 5 degrees of arc from the direction towards the Sun during the Winter solstice. That's close enough to assume it's the same direction for our purposes.
So as you look at the second picture, with the Earth at the Winter solstice point, towards the Sun, the declination value tells you how far below ('cause it's negative) the Earth's equatorial plane you'll see the centre of the Galaxy. Since you're looking below, the plane of the equator has to be tilted up - as depicted in the 2nd one.
 
Bandersnatch said:
It is the second picture, agreed. But. The angle you're talking about is in a plane roughly parallel to the Sun-Galactic Centre direction. That is, the right ascension of the Galactic North is approx 13h, close to the direction of the autumnal equinox (to the right of the picture). In the picture it represents more the general slant of the plane of the ecliptic than that of the equatorial plane.
To be clear, I meant the 2nd picture in the OP's reference, or this PF thread.
Image:
there-planes-angles_no-earth-09oct2016-jpg.jpg
 
Drakkith said:
To be clear
Fair enough. I meant OP's drawings when referring to the 2nd picture in my post. The point stands, though.
In the picture from the reference you can see that the two component angles of displacement from the axis of the ecliptic are roughly at 90 degrees. The tilting of the ecliptic w/r to the galactic equatorial plane is pretty much sidewise, so how much the two are inclined does almost nothing to the direction towards the core. You could rotate the entire galactic plane w/r to the ecliptic around the line connecting the nodes (i.e. vary the 60.2 deg angle over full 360 degrees) and you'd get the direction towards the core stay almost the same. That's why the sum of this angle with the axial tilt is a red herring.
 

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