A Map of Your Galaxy - The Milky Way

Understanding our galaxy, "The Milky Way."  An exercise that will expand your mind. 

I've got a future post planned for some Hubble Space Telescope wallpapers...my favorites, to be exact.  But before I get to that, I figure you need to put some context around what you are seeing, hence the galaxy and the map.   
(note:  click images for larger view)

Too many times people look at the Hubble pictures and go, "oh, that's cool" without even the slightest understanding of what they are actually viewing.  HST has given us a window into the galaxy mankind has never had before.  I want to try and bring that home by introducing you to a map of our galaxy.

That leads us to quick discussion on our galaxy, also known as the "Milky Way".  The Milky Way is the galaxy in which the "Solar System" is located.  The Solar System is our sun and anything drawn to the sun by the forces of gravity.

For those of you who slept through these classes (its alright, I skipped a lot myself...), I have some numbers for you:

• 1 light year = about 6 trillion miles
• Our galaxy has a total diameter of approximately 100,000 light years
• Our sun is about 26,000 light years from the central "bulge" of the galaxy
• It takes 200-250 million years for the sun to complete one orbit around that central "bulge"
• Surrounding the galaxy, there are approx 200 globular clusters, containing 1 million stars each
• Our galaxy contains roughly 200 billion stars 

This is your Milky Way galaxy.  This is the galaxy that contains our sun, and our pale blue dot - earth.  Looks pretty phenomenal eh?  That scale in the lower left is 10,000 light years.  You can use the numbers from above to do a little math on the size of our galaxy.  100,000 light years x 6 trillion miles = 600 quadrillion miles!  (hint, quadrillion comes after trillion, and looks like this:  600,000,000,000,000,000)

That's a good image, but it's top-down, 2D.  That's not how space works, so here is a side view, to give some depth and an understanding of the 3D nature of the beast...so to speak.  A side view will also give you some idea of the "bulge" (aka nucleus), the globular clusters, and the various "arms"...as well as the approximate position of our sun on one of those arms.

Here is another side view that highlights our location in the galaxy, aka our solar system.  In the above image you see the "local arm", obviously containing our sun.  This tilted image does a little bit better job of bringing it home when you think about "you are here" (sort of like the mall map when you need to find the food court).

Alright, your mind should be sufficiently blown at this moment.  You may also be asking yourself - wait, what's all this about the "universe"?  Well a universe is a collection of galaxies.  The Milky Way is one of the hundreds of billions of observable galaxies in what is traditionally known as the "observable universe".  So take these numbers and start doing this with them n^n (n raised to the n).  If your mind wasn't blown before, it should be ass-ploded by now.  And oh, yes, there is a reason for the word "observable" in "observable universe".  It implies that we know, but are not able to fully observe outside of this universe...in other words, we think we see our tip of the iceberg.  Understanding the numbers from above, and the sheer size of that "iceberg tip",  it should be clear that the possibilities are infinite.  So infinite that even if we could put numbers on it, they wouldn't mean anything to us, as it would be larger and more complex than anything we could understand.

To wrap up, here is an absolutely amazing map of our galaxy provided by National Geographic.  This has more information on it than any of the above pictures, but wouldn't make any sense if you didn't think about the numbers and the context.  Still, our feeble human minds have difficulty grasping the sheer size of our galaxy, let alone the possibilities that exist in the universe.  It also has a rocking "You are Here" label to make you feel really, really small.  Leave it to Nat Geo to make a poster like this one, god I love those people.  Click for high resolution!  (larger original is here) 

note:  on this day, in 1971, NASA's spacecraft 'Mariner 9' reached Mars, and became the first object to orbit another planet! let's keep kicking ass, pushing the envelope, and going further, and further away from "home".