Wikipedia:Reference desk/Archives/Science/2018 August 16

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August 16

Seeing the brightness of a city in the horizon from the sea

In the sea, how far away can you see the glare of a city in the sky (independent of any lighthouse), if you can distinguish it at all?--Doroletho (talk) 12:46, 16 August 2018 (UTC)

Too many variables to quantify. (At least 40 miles from my experience) 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 18:27, 16 August 2018 (UTC)

With the naked eye and knowing what to look for, no clouds, at sea level, average air for this planet (average humidity, particulate matter etc.), no twilight, no moon: up to about 200 kilometers from the center of Tokyo, Seoul or Midtown Manhattan. A little less if you could turn off all lights outside the metropolitan area (looking at the shape of the suburbs, more reduction for New York and Seoul than Tokyo I think, Tokyo having a convex shore and New York having very far suburbs and a concave shoreline must account for the size difference (24 million vs. 40). South Korea has straightish edges but is very densely populated, maybe the DMZ lights are not an insignificant contribution to the distance either). Look up the brightness of the dimmest low stars you can see towards the city in a star catalog and do the same for exact same distance from the opposite horizon and you can detect Tokyo from almost 200 kilometers away (choose a night when weather maps show no clouds, volcanic ash or wildlife smoke and very similar amounts of water vapor for many hundreds of kilometers around you). You can see the city lights directly from much further from outer space (still over the ocean) Sagittarian Milky Way (talk) 20:36, 16 August 2018 (UTC)

At least 80 km from the deck of a yacht (height is probably not important). The clouds reflect a lot of glow back down.Greglocock (talk) 20:46, 16 August 2018 (UTC)

You can see the Skyglow from further away than the horizon distance suggests. The Skyglow is where light from streetlights is reflected by air, aerosols, and low cloud, and manifests as an orange glow above the city. LongHairedFop (talk) 13:20, 18 August 2018 (UTC)

If the streetlights have switched to white LEDs it won't be strongly colored anymore. Sagittarian Milky Way (talk) 05:55, 19 August 2018 (UTC)

I was hoping that the article on the Second Happy Time would give a number to answer this question, but as far as I can see, it doesn't. --76.69.47.228 (talk) 21:32, 16 August 2018 (UTC)

The Guinness Book of Records once said the brightest single artificial light in the world (or the one directly seen from the furthest distance with the naked eye?) was on the top of the Empire State Building and was visible from sea to like 50 miles which is about as far as you can see something that high from sea level (excluding the rare places below sea level). Not the holiday lights, higher, maybe it was those very bright orange high pressure sodium lights within several human heights of where King Kong fell that turned on at midnight when the holiday lights turned off. As there's a lot of structures taller than that now this distance has probably been beaten. Sagittarian Milky Way (talk) 21:58, 16 August 2018 (UTC)

Driving from LA to Phoenix, AZ, behind Yuma, the lights of Phoenix can bee seen in the sky at night, but it still takes 8 hrs to arrive at Phoenix. --Hans Haase (有问题吗) 13:31, 18 August 2018 (UTC)

And there are no cities or towns between Los Angeles and Phoenix? --Guy Macon (talk) 01:47, 19 August 2018 (UTC)

According to Google Pro, the direct drive (which is close to being straight) is 373 miles, would take 5h 23m in "usual traffic", and the only towns of any significant size between them are Riverside, 54 miles from Los Angeles but essentially on the eastern edge of the same conurbation (thus about 320 miles from Phoenix) and Palm Springs, around 90 miles from Los Angeles but small by comparison. {The poster formerly known as 87.81.230.195} 94.0.130.143 (talk) 05:40, 19 August 2018 (UTC)

It'd be a bit odd going from LA to Phoenix via Yuma. Maybe Hans meant Blythe? It sure is the closest thing to a city on the I-10 between Palm Springs/Coachella and Phoenix. — Preceding unsigned comment added by 93.139.14.41 (talk) 20:17, 21 August 2018 (UTC)