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Are north and south in astronomy defined relative to Earth’s poles? What about “lateral” directions, since east and west are relative (no poles, ie. no east of
by pcmaffey 8y ago
Are north and south in astronomy defined relative to Earth’s poles? What about “lateral” directions, since east and west are relative (no poles, ie. no east of earth)?
- jessriedel 8y agoI don't know for sure how that's defined (I ctrl-f'd and it's not explained in the paper), but this says the "North" is to the right of the image, and from context it sounds like it's the north pole of the accretion disk, i.e., the direction of the rotation axis with the right-hand rule. > The approaching side of the large-scale jet in M87 is oriented west–northwest (position angle $\mathrm{PA}\approx 288^\circ ;$ in Paper VI this is called ${\mathrm{PA}}_{\mathrm{FJ}}$), or to the right and slightly up in the image.
- thro_away_n 8y agoIn paper I, Figure 3, it says North is to the top of the image and East is to the left.
- jessriedel 8y agoWhoop. You're right. I misread again.
- pi-squared 8y agoUsing the right-hand rule: knowing the direction of spinning, if you point your thumb up and wrap the other four fingers in the direction of rotation, the thumb will be pointing North. Oposite of that is South. East can then be defined along the direction of spinning (eastward or counterclockwise looked from North, the way Earth is spinning) and West - opposite to that, clockwise looked from North, opposite the direction of rotation.