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kmoonster t1_j7c8x37 wrote

How old? If a city had gas streetlights in the evening, those lights may have been extinguished once evening traffic slowed down.

It's also possible they used a different sequence of names for the hours and/or daylight savings.

[It is probably due to a combination of different definitions of time-setting, our modern lack of familiarity with night vision, and a little astronomy]

And there is also the different grades of darkness. A sunset at 5pm will have useful light until 6 or 7 depending on your latitude, though it's less obvious today with modern electric lights being ubiquitous. Where I am, you can make out trees against the sky for an hour or so after the sun goes behind the horizon, but you have to actively be looking for it in order to notice it. The presence of so many electric lights and headlights means your night-vision never has the chance to grow into it because those opsins are always being knocked back. Given time to properly form, your dark-vision can pick out a trail in an open area even a couple of hours (or more!) after sunset.

Combine this with a sense of how quickly the sun moves, and you can work out useful light after dark fairly easily. The sun moves through about 15 degrees of arc in an hour, and there are discernible amounts of useful light up to at least 18 degrees of arc below the horizon, sometimes more depending on weather -- and you can have well in excess of an hour before/after the sun is visible. Perhaps two hours or even more. And if the area has an open tree canopy, stars provide a fair amount of light if they are visible.

This page illustrates the different shades of twilight in a way that may be useful. https://www.timeanddate.com/astronomy/different-types-twilight.html

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[Note: keep in mind that both latitude and season will affect how long it takes to have the sun position itself 18-20 degrees below the horizon, as the sun rarely crosses at precisely 90 degrees. The sun moves along the hypotenuse of a right triangle, not the short leg. This means reaching 18 degrees of arc below the horizon means traveling *more* than 18 degrees of arc along its [apparent] path of motion, or more than the 1.2 hours it would need if it were travelling at a right-angle to the horizon. In mid-summer, you can experience twilight all night if you are a few miles from the Arctic/Antarctic Circle; while at the Equator twilight will short and relatively equal all year]

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edit: timezones are also a consideration. Until the railroads, all time was local time based on local solar noon. If you live at the far western or eastern edge of a modern time zone , you could be offset by up to two full clock-hours from someone living in your town 200 years ago -- one hour for the ~15 degrees of longitude comprising an average time zone, and one hour if your area practices daylight-savings. Time zones are measured from their theoretical central longitude, for instance where I live in Denver the 105th line of longitude literally runs through the middle of downtown (there is even a mark in the pavement where it lies). 105/15 = 7, and what do you know but Mountain Time is GMT - 7 (and we are roughly center of the Mountain Time Zone, local noon and clock noon are fairly close).

But if you live in New York, you are on the very east edge of Eastern Time and your local noon is a full hour offset from someone living in Indianapolis on the far west edge of the same time zone. If you live in northwest Indiana (Gary area) you may even be TWO hours off due to some of those counties following Chicago time (Central Time) due to their proximity to that city -- add to this that Indiana as a state does not universally do daylight savings and...you can easily find one to three hours where your modern clock could vary from the historical clock of someone living there in the early 1800s. (The new American government opened Indiana Territory to settlement by non-Native people in 1791, and by the late 1820s it was approaching its modern form from a perspective of demographics and rough political boundaries - think the world of Mark Twain and Abraham Lincoln.)

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Once_Wise t1_j7djz9p wrote

>Combine this with a sense of how quickly the sun moves, and you can work out useful light after dark fairly easily. The sun moves through about 15 degrees of arc in an hour, and there are discernible amounts of useful light up to at least 18 degrees of arc below the horizon, sometimes more depending on weather -- and you can have well in excess of an hour before/after the sun is visible. Perhaps two hours or even more. And if the area has an open tree canopy, stars provide a fair amount of light if they are visible.

It is surprising to us city folks like me how much one can see by starlight alone. I have done a fair amount of camping in the California deserts, and it is amazing how bright a moonless starlit night can be. Several times I have been able to walk along a dirt road by starlight alone. About 3am, your eyes are used to the dark, you cannot make out any clear features but there are no trees, the ground is relatively light colored and while it would be dangerous to walk cross country, I have done it on a dirt desert road at night. It was BLM land where you can camp and find spots with no other people for miles around. On other moonlit nights I have read a newspaper inside my tent after my eyes were used to the dark. I imagine that people in days when there was very little artificial light, and where they had grown up and were used to these conditions and their surroundings, could do quite well at night. And most nights have at least some moonlight. I learned this quite early when our former Marine, Boy Scout leader made us leave our flashlights back in camp and took us on night hikes, navigating by moonlight alone. Along the way he would stop and tell scary stories. But that was ages ago. Fear of lawsuits would probably prohibit this kind of thing today.

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