Caption: Milky Way astrophysical map: "A map/artist's conception of the spiral arm structure of the Milky Way with the two main Milky Way spiral arms and the Milky Way bar bulge of stars." (Moderately edited.)

Features:

1. Because it is quite modern (i.e., from 2008) and generated by highly reputably authors (i.e., NASA, Jet Propulsion Laboratory (JPL), Caltech, Robert L. Hurt), yours truly believes the image is an accurate map for large features: i.e., Milky Way disk, Milky Way bar bulge, Milky Way spiral arms.

   The fine detail (particularly the coloration of the Milky Way spiral arms) is probably the only thing that is artist's conception.

2. In the de Vaucouleurs system, the Milky Way is thought to be a SB(rs)bc SB(rc)bc (e.g., Frommert & Kronberg 2005): i.e., a barred spiral intermediate between subtypes b and c and intermediate between ring (r) and no-ring (s).

   The type is NOT perfectly known because of classic can't see the forest for the trees situation.

   The Solar System is the Milky Way disk which is laced with interstellar dust which allows us only to see about a third???? of the Milky Way disk in the visible. Some other energy/frequency/wavelength bands (e.g., radio and infrared) allow us more and map to some accuracy the whole Milky Way.

3. The Milky Way spiral arms are:
   1. Carina-Sagittarius arm: a minor spiral arm.
   2. Norma arm: a minor spiral arm.
   3. Orion arm (AKA Orion-Cygnus arm, Orion spur, Local arm): a minor spiral arm.
   4. Outer arm: a minor spiral arm: an extension of the Norma arm.
   5. Perseus arm: one of the two major spiral arms.
   6. Scutum-Centaurus arm: one of the two major spiral arms.

4. NASA's infrared Spitzer Space Telescope has greatly helped to show that Milky spiral arm structure is dominated by just two major spiral arms coming off the ends of the Milky Way central bar. "Previously, the Milky Way was thought to possess four major spiral arms." (Moderately edited.)

5. Like most spiral galaxies most star formation happens in spiral arms in molecular clouds which are opaque brown because of dense concentrations interstellar dust.

   The interstellar dust permits the existence of the molecules which cools the interstellar medium (ISM) gas by radiating away heat energy as electromagnetic radiation (EMR) (principally in the infrared and radio) which lowers the gas pressure which allows runaway gravitational collapses which fragment into newly forming stars. The EMR output of the new stars is dominated by hot blue OB stars which provide ultraviolet light which ionizes the atomic hydrogen gas to create H II regions (dominated by ionized atomic hydrogen gas) which emit strongly the red Hα of hydrogen (following recombination to neutral atomic hydrogen gas) which gives the H II regions their pink glow.

   The upshot of the foregoing is that spiral arms are a complex and pretty mixture of colors: brown, blue, pink.

   Note that star formation is concentrated overwhelmingly in spiral arms, but within spiral arms the regions of star formation are pretty random.

6. The map also shows the Galactic coordinate system which has the Sun (and therefore the Earth) at the origin.

   The distances from the Sun are marked in light-years (ly).

   Note that 1 kiloparsec ≅ 3261.563777167433 ly ≅ 3261 ly ≅ 3000 ly.

7. The Sun is 8.0(7) kpc (i.e., 26.2(2.2) kly) from the Milky Way center (AKA Galactic center) (see Wikipedia: Galactic Center: Distance to the Galactic Center) and has orbital period in the range 225--250 Myr and orbital velocity 251 km/s (see Wikipedia: Sun).

8. The Milky Way has NO sharp edge, but the Milky Way disk radius ≅ 30 kpc, the Milk Way dark matter halo ⪆ 70 kpc, and the Milky Way formal turnaround radius ∼ 1 Mpc given Milk Way mass ∼ 10**12 M_☉.

   The formal turnaround radius is where a galaxy's (or larger astro-body's) gravity and its cosmological constant force cancel.