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# Astronomy/orientation

Question
I have had something on my mind recently, on a grand scale. The direction or orientation of something in space is all relative, for example, standing on the surface of the earth, relative to that, "up" and "down" are the directions perpendicular to the surface because we feel the gravity from the planet.  All the planets in our system orbit on an approximate plane, so at a particular spot on Earth, say, the North Pole exactly, my standing body will not be perpendicular to the "up" and "down" relative to the planetary  orbital plane because of the Earth's tilted axis (we say its "tilted" because we are referencing this plane, right?)

The thing I am wondering about is, if we go on the biggest scale we can, with whatever data and charting that is available about the orientation of planets and stars and galaxies, which way would "up" and "down" be?  My thinking so far has been:  Up/down is a certain way relative to the surface of Earth as we know, then, a certain way relative to the orbital plane around the Sun.  Then the Sun has its own orbital plane to the center of our galaxy.  Then our galaxy has it's own approximate orbital plane to the Local Group (though I read its near the center anyway).  Maybe there is some more in between I have not thought of, or we are able to go bigger with super clusters (at that point you would be looking to aim for the center of something because you are located somewhere in a spherical cluster).

Another way to word it might be, if I were to stand up and then draw a line through my head and feet that extended on infinitely in either direction, at what angle would the line intersect the orbital plane of …(the galaxies in our local group…or again, maybe something bigger?  Or, how would I have to stand/where would I have to stand on Earth for the line to go through the center of… (our Supercluster maybe…tentatively with all of this of course).

If its able to be answered, you can do cool things like figure out that if you lay down on your roof at a certain angle facing a certain area in the sky at night in the Fall and look out, you will be staring straight toward.. whatever it is we decided we were going to be relative to.

Hi Jan,

I don't know whether this answer will help you much or not. But for orientation purposes, I wouldn't go much beyond the plane of the Milky Way. Once you get out to the Virgo supercluster and beyond, the orbital planes (giving some notion of north or south (or up or down) are much more difficult to define.

So the best way to define large-scale orientation is with the galactic coordinate system. The North Galactic Pole is located at 12h51m,+27°.1 in the direction of Coma Berenices.

The South Galactic Pole is at 0h51m,-27°.1 in the direction of Sculptor.

The Galactic Centre is at 17h46m,-28°.9 in the direction of Sagittarius.

So if you were standing at an angle, with Coma Berenices over your head and you were facing Sagittarius, you'd be aligned with the Milky Way galaxy, looking directly at its centre.

If you were looking at Virgo (12h 31m, +12°.4), you'd be looking at the centre of the local supercluster. North and south (up or down) of the supercluster is harder to define. But here's a few sources to help you understand the large scale structure of the supercluster and get you started on orienting yourself (if you really want to stretch it that far). http://adsabs.harvard.edu/full/1958AJ.....63..253D is deVaucouleurs' classic paper, with some more explanation found at https://www.cfa.harvard.edu/~dfabricant/huchra/seminar/lsc/

I hope that helps.

Prof. James Gort

Astronomy

Volunteer

#### James Gort

##### Expertise

Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.

##### Experience

I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.

Publications
StarDate, University of Texas, numerous Journal Publications