When you look at maps of Berlin made in the decades before 1989, it’s impossible not to notice the physical fact of the city's political divisions. Some maps replaced one half of the city with a blank space; others painfully warped geography to delete one side altogether.

Looking at maps of the city today, it seems like it's once again a unified whole. You’d have to work hard to pick out exactly where the wall once stood.

The same isn't true of aerial photographs, however. In 2013, astronaut Chris Hadfield took a photo of the city from the 200 mile-high vantage point of International Space Station, and something immediately stuck out. To the west, the lights are white; to the east, they’re yellow. The boundary is a sharp, clear line, mirroring where the wall once stood. Hadfield tweeted the photo with the comment

Berlin at night. Amazingly, I think the light bulbs still show the East/West division from orbit.

It’s not immediately obvious why this should be. After all, the wall fell over 20 years before Hadfield took his photo, and you’d imagine large chunks of infrastructure, including street lights, would have been replaced in that time, especially if the eastern ones were out of date. But apparently, not so much. Soon after Hadfield’s photo did the rounds on social media, Christa Mientus-Schirmer, a member of the city government, told the Guardian:

Although we’ve made a lot of progress in the 20 years since the wall fell, we haven’t had the money we would have liked to equalise the two parts of the city.

A member of Berlin’s street furniture department got a little more technical, telling the publication:

In the eastern part there are sodium vapour lamps with a yellower colour. And in the western parts there are fluorescent lamps... which produce a whiter colour.

The significance of the lights as a reminder of the once-divided city isn’t lost on residents, either. On the 25th anniversary of reunification in November 2014, an artist used 8,000 glowing balloons to recreate the wall's division:

Image: German Foreign Office.

There’s currently a push within the EU to replace a million streetlights throughout Europe with new, low-emisison models. These would give that whiter light, so it could be that, just as the remaining sections of the wall are disappearing, the light disparity will fade with time.

While we’re here, a few other things stick out when you view the city from above. That white blob in the centre of the image (and, incidentally, on the eastern side of the divide) is Alexanderplatz, a central square and transit hub that’s undergone renovation since reunification. This explains its relative brightness compared to the yellower areas around it:

This triangular area of brightness on the top left is Tegel airport – you’d have a hard job missing it as an airline pilot:

And finally, here's a photo taken from space of Berlin during the day by the European space agency and beamed back to earth via laser:

Click for a larger image.

Not a division in sight.