Galactic Map Projections

One of my absolute favorite scenes from The West Wing (one of my favorite shows) wasn't about politics, or war, or even the President. Instead, it was a quirky plea to change the default map projection used when teaching children about the world. For your amusement, here's the clip...

sorry - clip has been removed from YouTube. I'm sure you can search and find the West Wing clip about map projections with little effort...

For the curious, some more details about the Gall-Peters projection!

Map projection isn't just a concern for cartographers, city planners, or ocean travelers. Astronomers deal with maps all the time as well! (Sometimes we astronomers forget this.) For example: one of my absolute favorite graphs from the last decade in astronomy comes from the SDSS, and is titled the "Field of Streams"...

Credit: Vasily Belokurov, SDSS-II Collaboration
This is a map of very faint sub-structure seen in our Galaxy using the SDSS. To give you a sense of scale, here is a comparable region (angularly speaking) of Earth using an even-spaced grid of lat/lon as in the figure above. Distortion of the far northern latitudes is (or should be) very apparent!



So let's playfully extend the logic from the West Wing. If using traditional Earthly map projection can lead to generations of international strife, then our concern for heavenly projections should be far greater! Consider the interstellar politics at play, and the need to avoid a false sense of Orion-Imperialism. I hereby create the Organization of Astronomers for Celestial Equality (OACE - now accepting membership applications).

Let us consider, what does your Galaxy really look like?

For this example, I've grabbed 2.5 million random stars from 2MASS, a famous infrared all-sky survey. Here is a density map of the Milky Way (from our vantage point) in the most basic map projection: uniform steps in latitude and longitude.


Here is the same data in a handful of other projections...
Sinusoidal

Robinson


Mercator

Hammer

and my personal favorite of the set...
Goode Homolosine

Look at how far the LMC and SMC appear to move between projections! What do you think, which is the best projection? Which is the most accurate for astronomy?

6 comments:

  1. Replies
    1. I'm a big fan of Robinson for day to day mapping

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  2. I usually like Aitoff or Hammer :) .

    ReplyDelete
  3. This has been my point exactly! For many centuries scientists on Earth have been using biased, Geocentric standards for measurement and exploration... Since Copernicus there have been a few rebels who have attempted to alter this ego-centric view of the universe...
    I propose a new system of standards based on the stability of either the aftermath of the big bang or the centroid of dark matter upon which to base a new, non-local standard of measurement that doesn't rely upon the truly obsolete standard of Earth Latitudes and Longitudes...

    ReplyDelete
    Replies
    1. The fatal flaw here is that there is no stable center of the universe from the big bang, nor a single centroid of dark mater. The observable universe is, by construction, centered around ourselves. The universe is thus and always ego-centric in our vantage point.

      Latitude and Longitude in the sky are ideal coordinates for the observed celestial sphere.

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    2. This was the argument for the early European mapmakers... also the argument for the early Chinese astrologers... Each, in his own way, assumed that they were the center of all the perceived... It's a fallacious argument in all cases... and definitely in this one...

      Delete

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