The crew said it was "like two galaxies swirling near each other."

As a country boy from the Western U.S., the D.C.-Maryland-Baltimore area seems like a sprawling metropolis that might get a little thinner in places, but never really ends. Though I haven't quite got my bearings yet, the astronauts who crew the International Space Station (ISS) have a birds-eye view on the hustle and bustle of the region. 

Tweeting from space, the ISS crew shared a picture of D.C. and Baltimore at night.

"Thx!" See, astronauts are hip with the text lingo. 

The bright white mess of stars on the right is Baltimore, then, and the web-like fissure of orange light is Washington, D.C. If the twin cities really were galaxies, D.C. would likely be much older and made up of mature helium stars instead of hydrogen (or at least significantly farther away and red-shifted) than the younger, bright-buring Baltimore.

What's really happening?

Turns out the color difference is due to a difference in street lighting. Baltimore, thanks to its recent Bmore Bright campaign, is a fully LED-lit city. LEDs have a cooler, bluish light and are also longer-lasting and more energy-efficient. D.C. has mostly high-pressure sodium lights, though the shift to LEDs is coming.

Knowing that, what can you spot in the image? You can check out the full-resolution, Creative Commons image here.

You can note a pretty clear boundary between the cities. Maryland suburbs seem to have a variety of lighting, while D.C. is consistent. In Baltimore, the Seagirt Marine Terminal and Mid-Atlantic Terminal port facilities have that orangish sodium-lamp glow right up next to the city’s white LED streetlights.

On the bay side of the Baltimore Beltway Francis Scott Key Bridge, the Sparrows Point warehouse facilities are blue-white, which hints at LEDs or other bright-burning lights.

What do you spot? What are your thoughts on street lighting—is LED a little harsh-looking? Enlighten us with a comment!