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Milky Way Visualization and Perception

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#1 BQ Octantis

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Posted 15 July 2017 - 06:02 AM

Moving to the middle of the Australian Outback afforded me the opportunity to see the core of the Milky Way directly at zenith—a feat unimaginable in the northern hemisphere. The view of our galaxy from its center to the Southern Cross is obscenely bright—the brightest of the full disk—with obvious dark lanes crisscrossing the brightness. I wanted to better understand what I was seeing, but all the visualization maps I found left correlation with the galactic structure too much to the imagination.


I stumbled across a plan view of the galaxy by Robert Hurt of Caltech (published in 2008) that reminded me of a seating chart for an opera. I found I could use this optic against ESO's wicked 360˚ panorama of the galaxy to finally appreciate what I was seeing. I created a rectilinear projection of the central 120˚ swath and mapped it to Hurt's seating chart; this allowed me to perceive where we are in the galaxy and how we're moving relative to what we can see. This has resulted in a completely different perspective when I go out and observe it.


Opera Guide to Visualizing the Galaxy

The galactic hub is center stage. The galaxy is comprised of two full spiral arms (the Centaurus Arm, originating in front of the hub, just left of center stage, and the Perseus Arm, originating behind the hub, just right of center stage). It also contains several more weakly defined arm-like structures. Our seat in the solar system is in a weak structure (the Orion Spur) that joins the two, with the Perseus arm coming off the stage to the left and wrapping around behind us and ending offstage to our right. When we look center stage , we're looking through the Centaurus Arm and at least three additional structures (the Sagittarius Arm, the Norma Arm, and the Near 3kpc Arm). All of these structures are coming with us in our clockwise march (from above) around the core. The galactic structure toward Eta Carinae is coming toward us; the structure toward Scutum is moving away.


While all of this may seem trivial, it's impressive to recognize that this is the largest structure for which a single human can appreciate his or her orientation with the naked eye. This provides a powerful perspective when sharing cosmology with a budding or aspiring astronomer; it's fun to conclude with the fact that the galaxy has only made 30 full turns in the entire existence of the Earth and less than one in all of humanity.





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#2 edwincjones


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Posted 15 July 2017 - 08:46 AM

no, no, no-delete this thread before I start planing at trip to Australia to see the MW






too late-  bangbang.gif

Edited by edwincjones, 15 July 2017 - 08:52 AM.

#3 GlennLeDrew



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Posted 15 July 2017 - 02:30 PM

Good job! You've rectified the projections nicely.This reminds me of my own explorations in visualizing Galactic structure, commencing in the mid '90s. Next up, you might consider three more such charts, centered at the other cardinal longitudes of 90, 180 and 270 degrees, to complete the picture. Of course, those other directions are rather less spectacular.


Other than the central bulge extensions and several 'windows' which afford a clear view to distances of 10,000+ light-years, most of the structures we see near disk plane of the milky way are confined to a couple or few thousand light-years. And so a similar effort for which the plan view reference is limited to a horizon of no more than 10,000 l-y would be useful. This would permit to better bring out and highlight the nearer molecular (dark) clouds and star-forming regions which a Galaxy-wide presentation tends to subsume under the really big picture presentation.

#4 BQ Octantis

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Posted 15 July 2017 - 07:44 PM

I was out again last night at 9:30, with the core a mere 1.5 hours from zenith. I oriented my view along the galactic plane (as in the panorama), and it suddenly struck me how the core looks like a giant pair of lips, pursed and ready to smack anyone who dares to stare for too long.


I admired the Centaurus arm, starting 35˚ left of center stage, whipping to the right across the stage and then heading directly away from me at around 55˚ right of center stage. The weaker Sagittarius arm went along for the ride in front of Centaurus and provided some added brightness; then—upon Centaurus's departure—it held its own out to 80˚ east of center stage, where it marched off into the distance.


The real magic happened when I perceived the Perseus arm, starting 10˚ right of center stage—obscured behind the core—whipping around behind the core to the left until it emerged from the darkness into view on the northeastern horizon. From there, it flanked me in a 210˚ turn, wrapping around behind me (and behind the Earth) to barely reappear at the southwestern horizon, where it continued off away from me beyond my view to the edge of the galaxy…

#5 Arthur L

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Posted 16 July 2017 - 09:12 AM

Yeah boy I am saving now for a trip down under.

Probably can only afford a one way ticket. 

Thanks for posting.

#6 MarioJumanji


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Posted 18 July 2017 - 03:08 PM

Why is my seat facing the back of the opera house?

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