Is the yearly cycle of varying daylight durations from day to day throughout time consistent? Is the cycle we have today the same as in the 17th century?

Submitted by meellowstar t3_10u9kid in askscience

I'm sitting on my thesis for my history class for uni and analyzing some old local policies from 1718 (from a city government in Palatinate, germany) , which told the citizens to bring a light source with them if they wanted to go outside after a specific point in time in the evening. I was a little bit confused about the determined point of time, being 10pm in summer and 8pm in winter. I thought, why would they set the time that late in winter? Where I live in December at 5pm it's already dark outside. Why force the people to carry a lightsource not until 8pm? Why not already at 5pm when it's already dark especially without having electrical light at that time. That applies to the summer time as well? Why having to bring a lit lantern at 10pm when there is still enough daylight so you wouldn't need a lantern. At least from todays perspective. And on top of that it's even more confusing if you take in account that we have winter and summer time. In the past winter time would be the normal time (UTC+1). Hence my question: How consistent is the yearly cycle of varying daylight duration from day to day throughout the year in a historical view? Was it the same in 16th century as today? Did it change throughout the millenia? And if so, how much did it change?

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AllenRBrady t1_j7bvkb8 wrote

I would consider the possibility that the local government was still using an antiquated system of measuring hours. Prior to the widespread adoption of mechanical clocks, hours were not a fixed length. Dawn to dusk was considered daytime, and dusk to dawn was considered night, and each was divided into 12 hours. The first canonical hour of the day was called Prime, and corresponded to 6am. When the sun was overhead, it was Sext. When the sun set, it was Vespers. The duration between Prime and Vespers was divided into 12 hours, regardless of how long daylight actually lasted. So in the summer, daytime hours were longer than nighttime hours, and in the winter, that was reversed.

That system was dominant throughout Europe until around 1600, when mechanical clocks finally became prevalent enough to replace older options like sundials. It seems possible to me that, by the early 1700s, certain jurisdictions might have still been working out the whole concept that all hours were the same length, and 8pm was daytime in summer and nighttime in winter. It's possible that the ordnance you refer to assumed 8pm was "a short time after sunset", while 10pm was "a long while after sunset, but not yet midnight."

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AllenRBrady t1_j7dim8j wrote

I just wanted to throw in a few calculations to round this theory out a bit. Looking at Mannheim, Germany, I see that the winter solstice this year will have 8 hours and 9 minutes of daylight, and the summer solstice will have 16 hours and 17 minutes. That means the winter night will last 951 minutes, and the summer night only 463. If we divide that into 12 hours, that makes a winter hour as long as 79.25 minutes, and a summer hour as short as 38.58 minutes.

So 8pm in the winter would translate to 158.5 minutes past Vespers (sunset), and 10pm in the summer would mean 154.3 minutes past Vespers. That's pretty consistent. If my speculation is correct, this law is saying you need to carry a light source if you're leaving your house 2.5 (modern) hours after sunset.

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GracefulFaller t1_j7md19z wrote

I know it’s a bit later after this was answered but does the sunset to darkness time change over the course of the year? If it doesn’t then the ordinance using your math would correspond to not too long after darkness they would be required to have a light. Which would make sense.

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jellifercuz t1_j7c2dzf wrote

Thank you, AllenRBrady, for this fascinating time-history.

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Connect_Office8072 t1_j7c2v5u wrote

This is probably the answer. I know that during winter and summer the daylight ‘hours” were much, much shorter.

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contractor_inquiries t1_j7fidzp wrote

Were hours based on position of sun, and thus all different lengths, or roughly the same amount?

Or were they just rough ideas of "chunk of time" and people didn't really think about it too much?

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AllenRBrady t1_j7grp7n wrote

I'm pretty sure that, in Europe at least, the local church or cathedral would be responsible for keeping the official time, and this would primarily be accomplished through the aid of a sundial. So if the sundial were properly calibrated, the daylight hours would have pretty regular.

I would have to assume that nighttime hours, or daytime hours on cloudy days, were often estimations at best. For the most part, the only folks who really cared what time it was were church officials who needed to determine when it was time to hold daily services. Everyone else would have just listed for the church bells.

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th30be t1_j7kyh9y wrote

Dang. What an interesting system. Thanks for that information. I am going to look more into time keeping.

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kafAZ t1_j7b3wzq wrote

Here is an NOAA site that allows you to enter in years between 1700 and 2100 and any latitude / longitude and get sunrise /sunset times for each day of the year. It looks to be pretty consistent throughout the years (changes are only a minute here and there).

Maybe it was a typo (a badly printed 5 may look like an 8)?

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hertzzogg t1_j7b5k4d wrote

This is the direction to turn your attention towards.

Length of daylight on any given day varies by latitude. In summer, the farther north of the equator, the longer the daylight.

Edit=180

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mfb- t1_j7bfg8y wrote

> In winter, the farther north of the equator, the longer the daylight.

The opposite. The farther away you are from the equator (i.e. farther north as OP asks about Germany) the shorter the daylight in winter.

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darrellbear t1_j7bfn4i wrote

You have that backwards--the farther north the shorter the daylight during winter. Cross the arctic circle in winter, the sun doesn't rise at all. Conversely, during summer, the farther north the longer the daylight. Cross the arctic circle, the sun doesn't set at all during summer.

The same applies in the southern hemisphere, of course.

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SteampunkSniper t1_j7blzvj wrote

No, the north pole is a blackout regardless of time of day in winter. You’re going the wrong direction. Summer it stays light longer.

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CreatureOfPrometheus t1_j7b1kpc wrote

The variation in day length is caused by Earth-Sun geometry, so any change from 1700 to now is negligible.

I can think of two factors that might contribute:

  1. Was there summer time/winter time in that locale in 1718? If not, then "10pm dark" then should be like "11pm dark" now.

  2. In 1718, there were probably no time zones, so 12pm was measured from local solar noon. Depending on where you are in your timezone, there could be a shift of clock noon from solar noon. It's usually mild (should be <30 min), but is worse in some places due to political boundaries. It would shift both summer and winter sunset times the same, though.

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AUniquePerspective t1_j7ccxje wrote

I don't know if it is the same for cities in Rheinland-Pfalz but I believe Berlin abandoned Local Mean Time in 1893 in favor of CET (Central European Time UTC +1). Currently Rheinland-Pfalz uses CET in winter and CEST (Central European Summer Time UTC +2) in summer.

LMT Local mean time differs from apparent solar time as can be observed with a sundial in that time is constant with LMT but the speed of time varies with a sundial.

This is all confusing without examples so...

At Mainz on this year's summer solstice, the sun will rise at 5:17 CEST, reach solar noon at 13:28, and set at 21:39 CEST.

And on this year's winter solstice, the sun will rise at 8:22 CET, reach solar noon at 12:25, and set at 16:27 CET.

There are (by subtraction) 8 hours ten minutes between noon and sunset midsummer and 4 hours between noon and sunset midwinter. This explains the timing of the candle law.

Edit: But it's also important to recall that sunset isn't the time it gets too dark. There are 3 phases of twilight. During Civil Twilight it is generally possible to do outdoor activities though the sun is below the horizon. During nautical twilight, if the sky is clear, the brighter stars are visible and so is the horizon. During astronomical twilight, some stars that would otherwise be visible are obscured by sunlight.

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yanessa t1_j7cdk0u wrote

ad1) summer/winter time was introduced in the 20th century (first official use 1908 inOntario, Canada) so n.a. here

ad2) time zones started being used in the latter 19th century for railways

the differing hour length from medieval time measurement is a better bet

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mfb- t1_j7b0wur wrote

The length of daylight on a given calendar day was essentially the same as today, there are some long-term variations but they don't matter here. Three things to consider:

  • 1718 was long before people agreed on specific time zones. /r/AskHistorians would be a good place to ask about timekeeping details.
  • The length of the day depends on the latitude, so your own daylight hours only matter if you live at the same approximate latitude.
  • Who says the rule was based on the time of sunset? Maybe the time from sunset to 8 pm had so many people still awake and/or on the streets that it wasn't important to mandate light carrying.
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TheOneBlueGecko t1_j7b7y4l wrote

There are different levels of darkness. Astronomical twlight (when it basically seems completely dark) is 7:30ish in winter there. It is possible that the law also starts a bit after that point as people who were caught out after sunset might still be heading home and not yet have a light with them.

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bobjkelly t1_j7bkvwa wrote

The cycle is pretty consistent year to year but there are some long term cycles. These cycles take thousands of years, however, so probably not much difference from 1718 to here. One is that the tile of the earth relative to its orbit varies between 22.1% and 24.5% in a cycle of 41,000 years. It currently is about in the middle at 23.4% but is slowly decreasing. This would impact amount of daylight. Also, there is a cycle where the earths axis wobbles. And a cycle where the earth's orbit changes from almost round (where it is now) to slightly more elliptical. And a cycle where the closest approach to the sun (currently Jan 3) and farthest distance from the sun (about July 4) slowly change dates. All of these (and probably others) will impact daylight durations but probably not very much in a few hundred years.

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gstormcrow80 t1_j7bp6fn wrote

The ‘wobble’ you mentioned is the answer I came here looking for.

The earth rotates like a spinning top, and the axial precession is on a 26,000 year cycle. The most noticeable effect is a change in the position of stars year to year, and it will eventually cause Polaris to be replaced as the ‘north star’ in another 3,200 years. Changes in day length are negligible, but present.

Humans have been aware of it and attempts to precisely measure and define it go back more than 2,000 years. The ancient Greek and Indian (ACTUAL Indian, not Native American) cultures both recorded attempts to define it.

https://en.m.wikipedia.org/wiki/Axial_precession

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Recent_Caregiver2027 t1_j7b9sgf wrote

not directly to your question but it seems like you thibk that winter time is day light savings when it's is actually "real" time (besides the variation that time zones bring). Day light savings in North America (where/if used) begins on the 2nd Sunday in March and ends on the 2nd Sunday in November. We are in DST "fake" time for 8 months of the year

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ersentenza t1_j7bnwxi wrote

>Why not already at 5pm when it's already dark especially without having electrical light at that time.

But also without bright electrical lights everywhere all the time people might just have been more accustomed to low light, so what is "already dark" to you today might have been "there is still enough light to see" back then.

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Whisperberry t1_j7bqnfr wrote

Your history prof might appreciate me mentioning the 1700s is the “18th century” not 17th century. Comes from years 0-100 being the first century and thus 101-200 (could be called the 100s) is the 2nd century, and so on.

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PerpetuallyLurking t1_j7bqfx3 wrote

Our experience with daylight savings time distorts the comparison. Without DST, could your local winter dark be pushed back to 6pm? And throw in a bad 6 that looks like an 8 and then someone miscopied and now you’re reading a typo that persisted.

And that’s assuming the locals were particularly punctual and hadn’t let the town clock run into disrepair and keep time poorly. Or maybe there were still enough people out and about from 5-8 and houses with lamps lit up that carrying your own wasn’t necessary until 8. There’s a lot of variables for each city, town, and village.

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CyberneticPanda t1_j7bsi0q wrote

It is very very close to consistent, but days are very slowly getting longer. Thanks to tidal interactions, the moon steals a little of Earth's angular momentum every year and gets a little further away. That makes the day a tiny bit longer and the tilt of the orbit a tiny bit bigger. At the start of the Triassic 252 million years ago, there were about 400 days per year, and the moon was about 6000 miles closer.

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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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Traditional_Story834 t1_j7chmfy wrote

They are fairly consistent but will vary over time and would not be the exact same every year. It depends on the time scale you choose. The differences are small in the year to year. Main thing to check out is precession, it takes the earth 26,000 years to complete one precession, part of the yearly difference you see. Also things like large earthquakes tend to speed up the rotation, think a figure skater pulling their arms to their body during a spin.

Another thing I would consider is the fact time zones didn't exist back then like now, not sure you could confirm their 8 and 10 pm were in fact the same 8 and 10 pm they experience today as time zones didn't exist until after the 1880s.

Also the time they would need light will vary between those two times in the evening as they represent the extremes between the two seasons. So at the height of summer your good until 10pm, the bottom of winter you need it at 5pm, but in the middle of fall you might need it at 7:30pm.

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Only_Philosopher7351 t1_j7cuvun wrote

Although keeping time is a human invention and was only agreed upon relatively recently, variations in the earth's wobble around its axis have lead to shorter and longer amounts of sunlight further away from the equator.

But these variations are part of a long cycle (Milankovitch cycles) on observatories like Newgrange and Stonehenge prove that the position of the sun in the northern hemisphere has been very consistent for the last 10,000 or so years.

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znark t1_j7d86bp wrote

There is also Gregorian calendar reform to consider. The calendar had shifted from the seasons because of inaccuracy of the Julian calendar. It was 10 days in 1582 when the most of Catholic countries adopter new calendar. I think Palatinate was Protestant and transitioned in 1700.

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meellowstar OP t1_j7f43ax wrote

Thank you very much everyone for answering in such detail and with so many different approaches! You guys are awesome! Different time zones for each city thats crazy to imagine. How different the people lived and thought about things in the past compared to us nowaday, even different perceptions of time. I'm going to finish my thesis now. But it was a blast reading all of your answers and theories.

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