<p>I don't think it's possible to have a change in the ratio of day to night when averaged on a yearly basis.  To do so would require either a nonlinear change in the Earth's rotation or a significant shift in the polar axis tilt within a year.<br>
If the rotation were simply slowing down over time, the year-averaged ratio would be the same every year (only the number of days in a year would change).  Similarly, the only way a polar tilt could cause a change would be if the change in angle occurred at some (sinusoidal) rate not an integral ratio of the orbital period (year).<br>
Either of those putative mechanisms can only change the per-year ratio by producing a day/night ratio in "summer" that is not the inverse of the "winter" ratio, <strong>and</strong> producing a <strong>different</strong> non-inverse the following year.  (I'm oversimplifying a bit, since the elliptic orbit produces a repeatable asymmetry in the Sun's zenith pattern).</p>

CC BY-SA 3.0
2016-12-02T14:06:53.530Z
I am trying to understand your last point in light of my historical subquestion. Do you mean that, with an incomplete sample that averages out winter and summer rather than the whole year, one might have the impression of a change in the ratio of day to night? In other words, the ratio of day to night per month changes in that sometimes the extremes flatten out and the mid-seasons pick up the difference, and in this case, comparing only the month of January over several years might lead to the inference that there is trend in the ratio?
Modal
CC BY-SA 3.0
2016-12-02T14:13:37.697Z
@Modal I think you could say that -- suppose there's some polar axis wobble. Then Januarys might get darker, but Julys would get lighter.
Carl Witthoft
CC BY-SA 3.0
2016-12-03T14:50:18.873Z
If change the axis of rotation, you change the latitude of every point on earth. That'll effect day/night ratio over the course of a year. Such changes happen, but are quite small: Japan Quake May Have Shortened Earth Days, Moved Axis: https://www.nasa.gov/topics/earth/features/japanquake/earth20110314.html "The position of Earth's figure axis also changes all the time, by about 1 meter (3.3 feet) over the course of a year, or about six times more than the change that should have been caused by the Japan quake." You might get a few microseconds excess day or night in a given year in Montreal.
Wayfaring Stranger
CC BY-SA 3.0
2016-12-02T13:06:13.010Z
2016-12-02T13:06:13.010Z
Carl Witthoft
<p>Over a year, the ratio of daylight changes, e.g. in Montreal there is more daylight in the summer than in the winter.</p>

<p>I want to know if, given a bad data sample, e.g. five years, one might notice a trend of increasing or decreasing daylight ratios.</p>

<p>Here's why I ask. I'm doing research on the Dead Sea scrolls, and some of the fragments contain ratios that a scholar has argued represent daylight. What I'd like to know is a trend that the community of Qumran might have noticed in their dataset. They had a theory that darkness was increasing. I doubt their data was exhaustive, but I wonder if around Jerusalem there might have been a period of decreasing daylight ratios over a period of a few years roughly around 100 B.C.E.</p>

CC BY-SA 3.0
2016-12-02T05:36:32.780Z
Thanks. You make it clear that there is no such pattern, but do you know if, with the amateurish data that this ancient community would've had, they might have been led to infer a trend of increasing darkness?
Modal
CC BY-SA 3.0
2016-12-02T06:26:47.473Z
Interesting point about horology. The bias would have to make nights look increasing longer from year to year. As per the page you linked, a bias with the water clocks is that they make nights look shorter than they really are because the water flows more slowly when it's cold. However, this bias doesn't create a year-to-year trend.

There might be a bias in how they map the ratios from one year to the next. Perhaps they aligned the arrays incorrectly, and ended up comparing Jan with Feb, Feb with Mar, etc. I would need a more precise explanation as to how this might come to be.
Modal
CC BY-SA 3.0
2016-12-02T16:40:26.163Z
The darkness was indeed metaphorical, and that's what I'm focusing on in my paper. However, I think that it's important to understand the metaphor's natural vehicle before interpreting its target. There's a set of fractions in 4Q208-209, part of the incomplete 'Aramaic Astronomical Book', which are interpreted as daylight ratios. I wonder if they were trying to support their eschatology of increasing darkness/evil followed by a war between the children of light vs children of darkness by studying the daylight ratio over a few years.
Modal
CC BY-SA 3.0
2016-12-02T16:47:22.973Z
A relevant factor to consider is that they used a solar calendar was liable to a problem described [here](https://en.wikipedia.org/wiki/Enoch_calendar). And a paper related to this topic can be found [here](https://religion.fsu.edu/documents/Goff-Duke-DSD_021_02_176-210.pdf). They were near the Dead Sea, in present-day Israel (Qumran is the name of the site). We have translations, but the original scrolls are fragmented.
Modal
<amateur-observing>
Does the ratio of daylight change from year to year?
Modal
# Does the ratio of daylight change from year to year?

(Asked by: username_0 on 2016-12-02)

Over a year, the ratio of daylight changes, e.g. in Montreal there is more daylight in the summer than in the winter.

I want to know if, given a bad data sample, e.g. five years, one might notice a trend of increasing or decreasing daylight ratios.

Here's why I ask. I'm doing research on the Dead Sea scrolls, and some of the fragments contain ratios that a scholar has argued represent daylight. What I'd like to know is a trend that the community of Qumran might have noticed in their dataset. They had a theory that darkness was increasing. I doubt their data was exhaustive, but I wonder if around Jerusalem there might have been a period of decreasing daylight ratios over a period of a few years roughly around 100 B.C.E.

**Tags:** amateur-observing
> **Comments:**
> **username_0**: Thanks. You make it clear that there is no such pattern, but do you know if, with the amateurish data that this ancient community would've had, they might have been led to infer a trend of increasing darkness?  
> **username_0**: Interesting point about horology. The bias would have to make nights look increasing longer from year to year. As per the page you linked, a bias with the water clocks is that they make nights look shorter than they really are because the water flows more slowly when it's cold. However, this bias doesn't create a year-to-year trend.  There might be a bias in how they map the ratios from one year to the next. Perhaps they aligned the arrays incorrectly, and ended up comparing Jan with Feb, Feb with Mar, etc. I would need a more precise explanation as to how this might come to be.  
> **username_0**: The darkness was indeed metaphorical, and that's what I'm focusing on in my paper. However, I think that it's important to understand the metaphor's natural vehicle before interpreting its target. There's a set of fractions in 4Q208-209, part of the incomplete 'Aramaic Astronomical Book', which are interpreted as daylight ratios. I wonder if they were trying to support their eschatology of increasing darkness/evil followed by a war between the children of light vs children of darkness by studying the daylight ratio over a few years.  
> **username_0**: A relevant factor to consider is that they used a solar calendar was liable to a problem described [here](https://en.wikipedia.org/wiki/Enoch_calendar). And a paper related to this topic can be found [here](https://religion.fsu.edu/documents/Goff-Duke-DSD_021_02_176-210.pdf). They were near the Dead Sea, in present-day Israel (Qumran is the name of the site). We have translations, but the original scrolls are fragmented.  

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## 1 answers

### Answer by username_1 on 2016-12-02. Score: 2 | Accepted answer

I don't think it's possible to have a change in the ratio of day to night when averaged on a yearly basis. To do so would require either a nonlinear change in the Earth's rotation or a significant shift in the polar axis tilt within a year.  
If the rotation were simply slowing down over time, the year-averaged ratio would be the same every year (only the number of days in a year would change). Similarly, the only way a polar tilt could cause a change would be if the change in angle occurred at some (sinusoidal) rate not an integral ratio of the orbital period (year).  
Either of those putative mechanisms can only change the per-year ratio by producing a day/night ratio in "summer" that is not the inverse of the "winter" ratio, **and** producing a **different** non-inverse the following year. (I'm oversimplifying a bit, since the elliptic orbit produces a repeatable asymmetry in the Sun's zenith pattern).

> **Comments:**
> **username_0**: I am trying to understand your last point in light of my historical subquestion. Do you mean that, with an incomplete sample that averages out winter and summer rather than the whole year, one might have the impression of a change in the ratio of day to night? In other words, the ratio of day to night per month changes in that sometimes the extremes flatten out and the mid-seasons pick up the difference, and in this case, comparing only the month of January over several years might lead to the inference that there is trend in the ratio?  
> **username_1**: @Modal I think you could say that -- suppose there's some polar axis wobble. Then Januarys might get darker, but Julys would get lighter.  
> **username_2**: If change the axis of rotation, you change the latitude of every point on earth. That'll effect day/night ratio over the course of a year. Such changes happen, but are quite small: Japan Quake May Have Shortened Earth Days, Moved Axis: https://www.nasa.gov/topics/earth/features/japanquake/earth20110314.html "The position of Earth's figure axis also changes all the time, by about 1 meter (3.3 feet) over the course of a year, or about six times more than the change that should have been caused by the Japan quake." You might get a few microseconds excess day or night in a given year in Montreal.  

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